From: Martin KaFai Lau martin.lau@kernel.org

commit e65a5c6edbc6ca4853e6076bd81db1a410592a09 upstream.

This patch adds a few bpf mem allocator functions which will be used in the bpf_local_storage in a later patch.

bpf_mem_cache_alloc_flags(..., gfp_t flags) is added. When the flags == GFP_KERNEL, it will fallback to __alloc(..., GFP_KERNEL). bpf_local_storage knows its running context is sleepable (GFP_KERNEL) and provides a better guarantee on memory allocation.

bpf_local_storage has some uncommon cases that its selem cannot be reused immediately. It handles its own rcu_head and goes through a rcu_trace gp and then free it. bpf_mem_cache_raw_free() is added for direct free purpose without leaking the LLIST_NODE_SZ internal knowledge. During free time, the 'struct bpf_mem_alloc *ma' is no longer available. However, the caller should know if it is percpu memory or not and it can call different raw_free functions. bpf_local_storage does not support percpu value, so only the non-percpu 'bpf_mem_cache_raw_free()' is added in this patch.

Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Link: https://lore.kernel.org/r/20230322215246.1675516-2-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- include/linux/bpf_mem_alloc.h | 2 + kernel/bpf/memalloc.c | 78 ++++++++++++++++++++++++++++++----- 2 files changed, 69 insertions(+), 11 deletions(-)

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h index 3e164b8efaa9..7e7df2c473d2 100644 --- a/include/linux/bpf_mem_alloc.h +++ b/include/linux/bpf_mem_alloc.h @@ -24,5 +24,7 @@ void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr); /* kmem_cache_alloc/free equivalent: */ void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma); void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr); +void bpf_mem_cache_raw_free(void *ptr); +void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);

#endif /* _BPF_MEM_ALLOC_H */ diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index ace303a220ae..6382da64459a 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -121,15 +121,8 @@ static struct llist_node notrace *__llist_del_first(struct llist_head *head) return entry; }

-static void *__alloc(struct bpf_mem_cache *c, int node) +static void *__alloc(struct bpf_mem_cache *c, int node, gfp_t flags) { - /* Allocate, but don't deplete atomic reserves that typical - * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc - * will allocate from the current numa node which is what we - * want here. - */ - gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT; - if (c->percpu_size) { void **obj = kmalloc_node(c->percpu_size, flags, node); void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags); @@ -171,9 +164,29 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node) memcg = get_memcg(c); old_memcg = set_active_memcg(memcg); for (i = 0; i < cnt; i++) { - obj = __alloc(c, node); - if (!obj) - break; + /* + * free_by_rcu is only manipulated by irq work refill_work(). + * IRQ works on the same CPU are called sequentially, so it is + * safe to use __llist_del_first() here. If alloc_bulk() is + * invoked by the initial prefill, there will be no running + * refill_work(), so __llist_del_first() is fine as well. + * + * In most cases, objects on free_by_rcu are from the same CPU. + * If some objects come from other CPUs, it doesn't incur any + * harm because NUMA_NO_NODE means the preference for current + * numa node and it is not a guarantee. + */ + obj = __llist_del_first(&c->free_by_rcu); + if (!obj) { + /* Allocate, but don't deplete atomic reserves that typical + * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc + * will allocate from the current numa node which is what we + * want here. + */ + obj = __alloc(c, node, GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT); + if (!obj) + break; + } if (IS_ENABLED(CONFIG_PREEMPT_RT)) /* In RT irq_work runs in per-cpu kthread, so disable * interrupts to avoid preemption and interrupts and @@ -647,3 +660,46 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)

unit_free(this_cpu_ptr(ma->cache), ptr); } + +/* Directly does a kfree() without putting 'ptr' back to the free_llist + * for reuse and without waiting for a rcu_tasks_trace gp. + * The caller must first go through the rcu_tasks_trace gp for 'ptr' + * before calling bpf_mem_cache_raw_free(). + * It could be used when the rcu_tasks_trace callback does not have + * a hold on the original bpf_mem_alloc object that allocated the + * 'ptr'. This should only be used in the uncommon code path. + * Otherwise, the bpf_mem_alloc's free_llist cannot be refilled + * and may affect performance. + */ +void bpf_mem_cache_raw_free(void *ptr) +{ + if (!ptr) + return; + + kfree(ptr - LLIST_NODE_SZ); +} + +/* When flags == GFP_KERNEL, it signals that the caller will not cause + * deadlock when using kmalloc. bpf_mem_cache_alloc_flags() will use + * kmalloc if the free_llist is empty. + */ +void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags) +{ + struct bpf_mem_cache *c; + void *ret; + + c = this_cpu_ptr(ma->cache); + + ret = unit_alloc(c); + if (!ret && flags == GFP_KERNEL) { + struct mem_cgroup *memcg, *old_memcg; + + memcg = get_memcg(c); + old_memcg = set_active_memcg(memcg); + ret = __alloc(c, NUMA_NO_NODE, GFP_KERNEL | __GFP_NOWARN | __GFP_ACCOUNT); + set_active_memcg(old_memcg); + mem_cgroup_put(memcg); + } + + return !ret ? NULL : ret + LLIST_NODE_SZ; +}

From: Alexei Starovoitov ast@kernel.org

commit 12c8d0f4c8702f88a74973fb7ced85b59043b0ab upstream.

Rename: - struct rcu_head rcu; - struct llist_head free_by_rcu; - struct llist_head waiting_for_gp; - atomic_t call_rcu_in_progress; + struct llist_head free_by_rcu_ttrace; + struct llist_head waiting_for_gp_ttrace; + struct rcu_head rcu_ttrace; + atomic_t call_rcu_ttrace_in_progress; ... - static void do_call_rcu(struct bpf_mem_cache *c) + static void do_call_rcu_ttrace(struct bpf_mem_cache *c)

to better indicate intended use.

The 'tasks trace' is shortened to 'ttrace' to reduce verbosity. No functional changes.

Later patches will add free_by_rcu/waiting_for_gp fields to be used with normal RCU.

Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/bpf/20230706033447.54696-2-alexei.starovoitov@gmail.... Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- kernel/bpf/memalloc.c | 57 ++++++++++++++++++++++--------------------- 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index b9bdc9d81b9c..63b787128de8 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -99,10 +99,11 @@ struct bpf_mem_cache { int low_watermark, high_watermark, batch; int percpu_size;

- struct rcu_head rcu; - struct llist_head free_by_rcu; - struct llist_head waiting_for_gp; - atomic_t call_rcu_in_progress; + /* list of objects to be freed after RCU tasks trace GP */ + struct llist_head free_by_rcu_ttrace; + struct llist_head waiting_for_gp_ttrace; + struct rcu_head rcu_ttrace; + atomic_t call_rcu_ttrace_in_progress; };

struct bpf_mem_caches { @@ -165,18 +166,18 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node) old_memcg = set_active_memcg(memcg); for (i = 0; i < cnt; i++) { /* - * free_by_rcu is only manipulated by irq work refill_work(). + * free_by_rcu_ttrace is only manipulated by irq work refill_work(). * IRQ works on the same CPU are called sequentially, so it is * safe to use __llist_del_first() here. If alloc_bulk() is * invoked by the initial prefill, there will be no running * refill_work(), so __llist_del_first() is fine as well. * - * In most cases, objects on free_by_rcu are from the same CPU. + * In most cases, objects on free_by_rcu_ttrace are from the same CPU. * If some objects come from other CPUs, it doesn't incur any * harm because NUMA_NO_NODE means the preference for current * numa node and it is not a guarantee. */ - obj = __llist_del_first(&c->free_by_rcu); + obj = __llist_del_first(&c->free_by_rcu_ttrace); if (!obj) { /* Allocate, but don't deplete atomic reserves that typical * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc @@ -232,10 +233,10 @@ static void free_all(struct llist_node *llnode, bool percpu)

static void __free_rcu(struct rcu_head *head) { - struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu); + struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu_ttrace);

- free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size); - atomic_set(&c->call_rcu_in_progress, 0); + free_all(llist_del_all(&c->waiting_for_gp_ttrace), !!c->percpu_size); + atomic_set(&c->call_rcu_ttrace_in_progress, 0); }

static void __free_rcu_tasks_trace(struct rcu_head *head) @@ -250,31 +251,31 @@ static void enque_to_free(struct bpf_mem_cache *c, void *obj) struct llist_node *llnode = obj;

/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work. - * Nothing races to add to free_by_rcu list. + * Nothing races to add to free_by_rcu_ttrace list. */ - __llist_add(llnode, &c->free_by_rcu); + __llist_add(llnode, &c->free_by_rcu_ttrace); }

-static void do_call_rcu(struct bpf_mem_cache *c) +static void do_call_rcu_ttrace(struct bpf_mem_cache *c) { struct llist_node *llnode, *t;

- if (atomic_xchg(&c->call_rcu_in_progress, 1)) + if (atomic_xchg(&c->call_rcu_ttrace_in_progress, 1)) return;

- WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp)); - llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu)) - /* There is no concurrent __llist_add(waiting_for_gp) access. + WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp_ttrace)); + llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu_ttrace)) + /* There is no concurrent __llist_add(waiting_for_gp_ttrace) access. * It doesn't race with llist_del_all either. - * But there could be two concurrent llist_del_all(waiting_for_gp): + * But there could be two concurrent llist_del_all(waiting_for_gp_ttrace): * from __free_rcu() and from drain_mem_cache(). */ - __llist_add(llnode, &c->waiting_for_gp); + __llist_add(llnode, &c->waiting_for_gp_ttrace); /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish. * Then use call_rcu() to wait for normal progs to finish * and finally do free_one() on each element. */ - call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace); + call_rcu_tasks_trace(&c->rcu_ttrace, __free_rcu_tasks_trace); }

static void free_bulk(struct bpf_mem_cache *c) @@ -302,7 +303,7 @@ static void free_bulk(struct bpf_mem_cache *c) /* and drain free_llist_extra */ llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra)) enque_to_free(c, llnode); - do_call_rcu(c); + do_call_rcu_ttrace(c); }

static void bpf_mem_refill(struct irq_work *work) @@ -435,13 +436,13 @@ static void drain_mem_cache(struct bpf_mem_cache *c)

/* No progs are using this bpf_mem_cache, but htab_map_free() called * bpf_mem_cache_free() for all remaining elements and they can be in - * free_by_rcu or in waiting_for_gp lists, so drain those lists now. + * free_by_rcu_ttrace or in waiting_for_gp_ttrace lists, so drain those lists now. * - * Except for waiting_for_gp list, there are no concurrent operations + * Except for waiting_for_gp_ttrace list, there are no concurrent operations * on these lists, so it is safe to use __llist_del_all(). */ - free_all(__llist_del_all(&c->free_by_rcu), percpu); - free_all(llist_del_all(&c->waiting_for_gp), percpu); + free_all(__llist_del_all(&c->free_by_rcu_ttrace), percpu); + free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu); free_all(__llist_del_all(&c->free_llist), percpu); free_all(__llist_del_all(&c->free_llist_extra), percpu); } @@ -456,7 +457,7 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)

static void free_mem_alloc(struct bpf_mem_alloc *ma) { - /* waiting_for_gp lists was drained, but __free_rcu might + /* waiting_for_gp_ttrace lists was drained, but __free_rcu might * still execute. Wait for it now before we freeing percpu caches. */ rcu_barrier_tasks_trace(); @@ -521,7 +522,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) */ irq_work_sync(&c->refill_work); drain_mem_cache(c); - rcu_in_progress += atomic_read(&c->call_rcu_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); } /* objcg is the same across cpus */ if (c->objcg) @@ -536,7 +537,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) c = &cc->cache[i]; irq_work_sync(&c->refill_work); drain_mem_cache(c); - rcu_in_progress += atomic_read(&c->call_rcu_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); } } if (c->objcg)

From: Alexei Starovoitov ast@kernel.org

commit 05ae68656a8e9d9386ce4243fe992122fd29bb51 upstream.

Factor out inner body of alloc_bulk into separate helper. No functional changes.

Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/bpf/20230706033447.54696-5-alexei.starovoitov@gmail.... Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- kernel/bpf/memalloc.c | 46 ++++++++++++++++++++++++------------------- 1 file changed, 26 insertions(+), 20 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index 0cd863839557..0f45ea4259cb 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -154,11 +154,35 @@ static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c) #endif }

+static void add_obj_to_free_list(struct bpf_mem_cache *c, void *obj) +{ + unsigned long flags; + + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + /* In RT irq_work runs in per-cpu kthread, so disable + * interrupts to avoid preemption and interrupts and + * reduce the chance of bpf prog executing on this cpu + * when active counter is busy. + */ + local_irq_save(flags); + /* alloc_bulk runs from irq_work which will not preempt a bpf + * program that does unit_alloc/unit_free since IRQs are + * disabled there. There is no race to increment 'active' + * counter. It protects free_llist from corruption in case NMI + * bpf prog preempted this loop. + */ + WARN_ON_ONCE(local_inc_return(&c->active) != 1); + __llist_add(obj, &c->free_llist); + c->free_cnt++; + local_dec(&c->active); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + local_irq_restore(flags); +} + /* Mostly runs from irq_work except __init phase. */ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node) { struct mem_cgroup *memcg = NULL, *old_memcg; - unsigned long flags; void *obj; int i;

@@ -188,25 +212,7 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node) if (!obj) break; } - if (IS_ENABLED(CONFIG_PREEMPT_RT)) - /* In RT irq_work runs in per-cpu kthread, so disable - * interrupts to avoid preemption and interrupts and - * reduce the chance of bpf prog executing on this cpu - * when active counter is busy. - */ - local_irq_save(flags); - /* alloc_bulk runs from irq_work which will not preempt a bpf - * program that does unit_alloc/unit_free since IRQs are - * disabled there. There is no race to increment 'active' - * counter. It protects free_llist from corruption in case NMI - * bpf prog preempted this loop. - */ - WARN_ON_ONCE(local_inc_return(&c->active) != 1); - __llist_add(obj, &c->free_llist); - c->free_cnt++; - local_dec(&c->active); - if (IS_ENABLED(CONFIG_PREEMPT_RT)) - local_irq_restore(flags); + add_obj_to_free_list(c, obj); } set_active_memcg(old_memcg); mem_cgroup_put(memcg);

From: Hou Tao houtao1@huawei.com

commit 59be91e5e70a1aa91dfee8088b071f6d05c8a1a3 upstream.

The memory free logic in bpf memory allocator chains a RCU Tasks Trace grace period and a normal RCU grace period one after the other, so it can ensure that both sleepable and non-sleepable programs have finished.

With the introduction of rcu_trace_implies_rcu_gp(), __free_rcu_tasks_trace() can check whether or not a normal RCU grace period has also passed after a RCU Tasks Trace grace period has passed. If it is true, freeing these elements directly, else freeing through call_rcu().

Signed-off-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/r/20221014113946.965131-3-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- kernel/bpf/memalloc.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index 5c4e54e17f95..9a4fb4ea73ef 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -261,9 +261,13 @@ static void __free_rcu(struct rcu_head *head)

static void __free_rcu_tasks_trace(struct rcu_head *head) { - struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu); - - call_rcu(&c->rcu, __free_rcu); + /* If RCU Tasks Trace grace period implies RCU grace period, + * there is no need to invoke call_rcu(). + */ + if (rcu_trace_implies_rcu_gp()) + __free_rcu(head); + else + call_rcu(head, __free_rcu); }

static void enque_to_free(struct bpf_mem_cache *c, void *obj) @@ -292,8 +296,9 @@ static void do_call_rcu_ttrace(struct bpf_mem_cache *c) */ __llist_add(llnode, &c->waiting_for_gp_ttrace); /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish. - * Then use call_rcu() to wait for normal progs to finish - * and finally do free_one() on each element. + * If RCU Tasks Trace grace period implies RCU grace period, free + * these elements directly, else use call_rcu() to wait for normal + * progs to finish and finally do free_one() on each element. */ call_rcu_tasks_trace(&c->rcu_ttrace, __free_rcu_tasks_trace); }

From: Alexei Starovoitov ast@kernel.org

commit d114dde245f9115b73756203b03a633a6fc1b36a upstream.

The next patch will introduce cross-cpu llist access and existing irq_work_sync() + drain_mem_cache() + rcu_barrier_tasks_trace() mechanism will not be enough, since irq_work_sync() + drain_mem_cache() on cpu A won't guarantee that llist on cpu A are empty. The free_bulk() on cpu B might add objects back to llist of cpu A. Add 'bool draining' flag. The modified sequence looks like: for_each_cpu: WRITE_ONCE(c->draining, true); // do_call_rcu_ttrace() won't be doing call_rcu() any more irq_work_sync(); // wait for irq_work callback (free_bulk) to finish drain_mem_cache(); // free all objects rcu_barrier_tasks_trace(); // wait for RCU callbacks to execute

Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/bpf/20230706033447.54696-8-alexei.starovoitov@gmail.... Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- kernel/bpf/memalloc.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index bbd3fa2bf119..16a57cc4992c 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -98,6 +98,7 @@ struct bpf_mem_cache { int free_cnt; int low_watermark, high_watermark, batch; int percpu_size; + bool draining;

/* list of objects to be freed after RCU tasks trace GP */ struct llist_head free_by_rcu_ttrace; @@ -301,6 +302,12 @@ static void do_call_rcu_ttrace(struct bpf_mem_cache *c) * from __free_rcu() and from drain_mem_cache(). */ __llist_add(llnode, &c->waiting_for_gp_ttrace); + + if (unlikely(READ_ONCE(c->draining))) { + __free_rcu(&c->rcu_ttrace); + return; + } + /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish. * If RCU Tasks Trace grace period implies RCU grace period, free * these elements directly, else use call_rcu() to wait for normal @@ -538,15 +545,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) rcu_in_progress = 0; for_each_possible_cpu(cpu) { c = per_cpu_ptr(ma->cache, cpu); - /* - * refill_work may be unfinished for PREEMPT_RT kernel - * in which irq work is invoked in a per-CPU RT thread. - * It is also possible for kernel with - * arch_irq_work_has_interrupt() being false and irq - * work is invoked in timer interrupt. So waiting for - * the completion of irq work to ease the handling of - * concurrency. - */ + WRITE_ONCE(c->draining, true); irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); @@ -562,6 +561,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) cc = per_cpu_ptr(ma->caches, cpu); for (i = 0; i < NUM_CACHES; i++) { c = &cc->cache[i]; + WRITE_ONCE(c->draining, true); irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);

From: Alexei Starovoitov ast@kernel.org

commit 5af6807bdb10d1af9d412d7d6c177ba8440adffb upstream.

Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu(). Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into per-cpu free list the _rcu() flavor waits for RCU grace period and then moves objects into free_by_rcu_ttrace list where they are waiting for RCU task trace grace period to be freed into slab.

The life cycle of objects: alloc: dequeue free_llist free: enqeueu free_llist free_rcu: enqueue free_by_rcu -> waiting_for_gp free_llist above high watermark -> free_by_rcu_ttrace after RCU GP waiting_for_gp -> free_by_rcu_ttrace free_by_rcu_ttrace -> waiting_for_gp_ttrace -> slab

Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/bpf/20230706033447.54696-13-alexei.starovoitov@gmail... Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- include/linux/bpf_mem_alloc.h | 2 + kernel/bpf/memalloc.c | 139 +++++++++++++++++++++++++++++++++- 2 files changed, 137 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h index 7e7df2c473d2..a57b7fc015fc 100644 --- a/include/linux/bpf_mem_alloc.h +++ b/include/linux/bpf_mem_alloc.h @@ -20,10 +20,12 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma); /* kmalloc/kfree equivalent: */ void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size); void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr); +void bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr);

/* kmem_cache_alloc/free equivalent: */ void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma); void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr); +void bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr); void bpf_mem_cache_raw_free(void *ptr); void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index fb390dcdbdaa..b6aaf92b5259 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -101,6 +101,15 @@ struct bpf_mem_cache { bool draining; struct bpf_mem_cache *tgt;

+ /* list of objects to be freed after RCU GP */ + struct llist_head free_by_rcu; + struct llist_node *free_by_rcu_tail; + struct llist_head waiting_for_gp; + struct llist_node *waiting_for_gp_tail; + struct rcu_head rcu; + atomic_t call_rcu_in_progress; + struct llist_head free_llist_extra_rcu; + /* list of objects to be freed after RCU tasks trace GP */ struct llist_head free_by_rcu_ttrace; struct llist_head waiting_for_gp_ttrace; @@ -342,6 +351,69 @@ static void free_bulk(struct bpf_mem_cache *c) do_call_rcu_ttrace(tgt); }

+static void __free_by_rcu(struct rcu_head *head) +{ + struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu); + struct bpf_mem_cache *tgt = c->tgt; + struct llist_node *llnode; + + llnode = llist_del_all(&c->waiting_for_gp); + if (!llnode) + goto out; + + llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace); + + /* Objects went through regular RCU GP. Send them to RCU tasks trace */ + do_call_rcu_ttrace(tgt); +out: + atomic_set(&c->call_rcu_in_progress, 0); +} + +static void check_free_by_rcu(struct bpf_mem_cache *c) +{ + struct llist_node *llnode, *t; + unsigned long flags; + + /* drain free_llist_extra_rcu */ + if (unlikely(!llist_empty(&c->free_llist_extra_rcu))) { + inc_active(c, &flags); + llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu)) + if (__llist_add(llnode, &c->free_by_rcu)) + c->free_by_rcu_tail = llnode; + dec_active(c, flags); + } + + if (llist_empty(&c->free_by_rcu)) + return; + + if (atomic_xchg(&c->call_rcu_in_progress, 1)) { + /* + * Instead of kmalloc-ing new rcu_head and triggering 10k + * call_rcu() to hit rcutree.qhimark and force RCU to notice + * the overload just ask RCU to hurry up. There could be many + * objects in free_by_rcu list. + * This hint reduces memory consumption for an artificial + * benchmark from 2 Gbyte to 150 Mbyte. + */ + rcu_request_urgent_qs_task(current); + return; + } + + WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp)); + + inc_active(c, &flags); + WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu)); + c->waiting_for_gp_tail = c->free_by_rcu_tail; + dec_active(c, flags); + + if (unlikely(READ_ONCE(c->draining))) { + free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size); + atomic_set(&c->call_rcu_in_progress, 0); + } else { + call_rcu_hurry(&c->rcu, __free_by_rcu); + } +} + static void bpf_mem_refill(struct irq_work *work) { struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work); @@ -356,6 +428,8 @@ static void bpf_mem_refill(struct irq_work *work) alloc_bulk(c, c->batch, NUMA_NO_NODE); else if (cnt > c->high_watermark) free_bulk(c); + + check_free_by_rcu(c); }

static void notrace irq_work_raise(struct bpf_mem_cache *c) @@ -483,6 +557,9 @@ static void drain_mem_cache(struct bpf_mem_cache *c) free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu); free_all(__llist_del_all(&c->free_llist), percpu); free_all(__llist_del_all(&c->free_llist_extra), percpu); + free_all(__llist_del_all(&c->free_by_rcu), percpu); + free_all(__llist_del_all(&c->free_llist_extra_rcu), percpu); + free_all(llist_del_all(&c->waiting_for_gp), percpu); }

static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma) @@ -495,11 +572,20 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)

static void free_mem_alloc(struct bpf_mem_alloc *ma) { - /* waiting_for_gp_ttrace lists was drained, but __free_rcu might - * still execute. Wait for it now before we freeing percpu caches. + /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks + * might still execute. Wait for them. + * + * rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(), + * but rcu_barrier_tasks_trace() and rcu_barrier() below are only used + * to wait for the pending __free_rcu_tasks_trace() and __free_rcu(), + * so if call_rcu(head, __free_rcu) is skipped due to + * rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by + * using rcu_trace_implies_rcu_gp() as well. */ - rcu_barrier_tasks_trace(); - rcu_barrier(); + rcu_barrier(); /* wait for __free_by_rcu */ + rcu_barrier_tasks_trace(); /* wait for __free_rcu */ + if (!rcu_trace_implies_rcu_gp()) + rcu_barrier(); free_mem_alloc_no_barrier(ma); }

@@ -553,6 +639,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_in_progress); } /* objcg is the same across cpus */ if (c->objcg) @@ -569,6 +656,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_in_progress); } } if (c->objcg) @@ -653,6 +741,27 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr) irq_work_raise(c); }

+static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr) +{ + struct llist_node *llnode = ptr - LLIST_NODE_SZ; + unsigned long flags; + + c->tgt = *(struct bpf_mem_cache **)llnode; + + local_irq_save(flags); + if (local_inc_return(&c->active) == 1) { + if (__llist_add(llnode, &c->free_by_rcu)) + c->free_by_rcu_tail = llnode; + } else { + llist_add(llnode, &c->free_llist_extra_rcu); + } + local_dec(&c->active); + local_irq_restore(flags); + + if (!atomic_read(&c->call_rcu_in_progress)) + irq_work_raise(c); +} + /* Called from BPF program or from sys_bpf syscall. * In both cases migration is disabled. */ @@ -686,6 +795,20 @@ void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr) unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr); }

+void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr) +{ + int idx; + + if (!ptr) + return; + + idx = bpf_mem_cache_idx(ksize(ptr - LLIST_NODE_SZ)); + if (idx < 0) + return; + + unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr); +} + void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma) { void *ret; @@ -702,6 +825,14 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr) unit_free(this_cpu_ptr(ma->cache), ptr); }

+void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr) +{ + if (!ptr) + return; + + unit_free_rcu(this_cpu_ptr(ma->cache), ptr); +} + /* Directly does a kfree() without putting 'ptr' back to the free_llist * for reuse and without waiting for a rcu_tasks_trace gp. * The caller must first go through the rcu_tasks_trace gp for 'ptr'

From: "Joel Fernandes (Google)" joel@joelfernandes.org

commit 3cb278e73be58bfb780ecd55129296d2f74c1fb7 upstream.

Implement timer-based RCU callback batching (also known as lazy callbacks). With this we save about 5-10% of power consumed due to RCU requests that happen when system is lightly loaded or idle.

By default, all async callbacks (queued via call_rcu) are marked lazy. An alternate API call_rcu_hurry() is provided for the few users, for example synchronize_rcu(), that need the old behavior.

The batch is flushed whenever a certain amount of time has passed, or the batch on a particular CPU grows too big. Also memory pressure will flush it in a future patch.

To handle several corner cases automagically (such as rcu_barrier() and hotplug), we re-use bypass lists which were originally introduced to address lock contention, to handle lazy CBs as well. The bypass list length has the lazy CB length included in it. A separate lazy CB length counter is also introduced to keep track of the number of lazy CBs.

[ paulmck: Fix formatting of inline call_rcu_lazy() definition. ] [ paulmck: Apply Zqiang feedback. ] [ paulmck: Apply s/call_rcu_flush/call_rcu_hurry/ feedback from Tejun Heo. ]

Suggested-by: Paul McKenney paulmck@kernel.org Acked-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- include/linux/rcupdate.h | 9 +++ kernel/rcu/Kconfig | 8 ++ kernel/rcu/rcu.h | 8 ++ kernel/rcu/tiny.c | 2 +- kernel/rcu/tree.c | 129 ++++++++++++++++++++----------- kernel/rcu/tree.h | 11 ++- kernel/rcu/tree_exp.h | 2 +- kernel/rcu/tree_nocb.h | 162 +++++++++++++++++++++++++++++++-------- 8 files changed, 248 insertions(+), 83 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6858cae98da9..96af37b312e9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -109,6 +109,15 @@ static inline int rcu_preempt_depth(void)

#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

+#ifdef CONFIG_RCU_LAZY +void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func); +#else +static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) +{ + call_rcu(head, func); +} +#endif + /* Internal to kernel */ void rcu_init(void); extern int rcu_scheduler_active; diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index d471d22a5e21..d78f6181c8aa 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -311,4 +311,12 @@ config TASKS_TRACE_RCU_READ_MB Say N here if you hate read-side memory barriers. Take the default if you are unsure.

+config RCU_LAZY + bool "RCU callback lazy invocation functionality" + depends on RCU_NOCB_CPU + default n + help + To save power, batch RCU callbacks and flush after delay, memory + pressure, or callback list growing too big. + endmenu # "RCU Subsystem" diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 49ff955ed203..af6a06b86298 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -481,6 +481,14 @@ enum rcutorture_type { INVALID_RCU_FLAVOR };

+#if defined(CONFIG_RCU_LAZY) +unsigned long rcu_lazy_get_jiffies_till_flush(void); +void rcu_lazy_set_jiffies_till_flush(unsigned long j); +#else +static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; } +static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { } +#endif + #if defined(CONFIG_TREE_RCU) void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, unsigned long *gp_seq); diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 21c040cba4bd..a767c78fdba9 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -44,7 +44,7 @@ static struct rcu_ctrlblk rcu_ctrlblk = {

void rcu_barrier(void) { - wait_rcu_gp(call_rcu); + wait_rcu_gp(call_rcu_hurry); } EXPORT_SYMBOL(rcu_barrier);

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 664ebd2da252..b135bfac923d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2777,47 +2777,8 @@ static void check_cb_ovld(struct rcu_data *rdp) raw_spin_unlock_rcu_node(rnp); }

-/** - * call_rcu() - Queue an RCU callback for invocation after a grace period. - * @head: structure to be used for queueing the RCU updates. - * @func: actual callback function to be invoked after the grace period - * - * The callback function will be invoked some time after a full grace - * period elapses, in other words after all pre-existing RCU read-side - * critical sections have completed. However, the callback function - * might well execute concurrently with RCU read-side critical sections - * that started after call_rcu() was invoked. - * - * RCU read-side critical sections are delimited by rcu_read_lock() - * and rcu_read_unlock(), and may be nested. In addition, but only in - * v5.0 and later, regions of code across which interrupts, preemption, - * or softirqs have been disabled also serve as RCU read-side critical - * sections. This includes hardware interrupt handlers, softirq handlers, - * and NMI handlers. - * - * Note that all CPUs must agree that the grace period extended beyond - * all pre-existing RCU read-side critical section. On systems with more - * than one CPU, this means that when "func()" is invoked, each CPU is - * guaranteed to have executed a full memory barrier since the end of its - * last RCU read-side critical section whose beginning preceded the call - * to call_rcu(). It also means that each CPU executing an RCU read-side - * critical section that continues beyond the start of "func()" must have - * executed a memory barrier after the call_rcu() but before the beginning - * of that RCU read-side critical section. Note that these guarantees - * include CPUs that are offline, idle, or executing in user mode, as - * well as CPUs that are executing in the kernel. - * - * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the - * resulting RCU callback function "func()", then both CPU A and CPU B are - * guaranteed to execute a full memory barrier during the time interval - * between the call to call_rcu() and the invocation of "func()" -- even - * if CPU A and CPU B are the same CPU (but again only if the system has - * more than one CPU). - * - * Implementation of these memory-ordering guarantees is described here: - * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. - */ -void call_rcu(struct rcu_head *head, rcu_callback_t func) +static void +__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy) { static atomic_t doublefrees; unsigned long flags; @@ -2858,7 +2819,7 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func) }

check_cb_ovld(rdp); - if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags)) + if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) return; // Enqueued onto ->nocb_bypass, so just leave. // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock. rcu_segcblist_enqueue(&rdp->cblist, head); @@ -2880,8 +2841,84 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func) local_irq_restore(flags); } } -EXPORT_SYMBOL_GPL(call_rcu);

+#ifdef CONFIG_RCU_LAZY +/** + * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and + * flush all lazy callbacks (including the new one) to the main ->cblist while + * doing so. + * + * @head: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all pre-existing RCU read-side + * critical sections have completed. + * + * Use this API instead of call_rcu() if you don't want the callback to be + * invoked after very long periods of time, which can happen on systems without + * memory pressure and on systems which are lightly loaded or mostly idle. + * This function will cause callbacks to be invoked sooner than later at the + * expense of extra power. Other than that, this function is identical to, and + * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory + * ordering and other functionality. + */ +void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) +{ + return __call_rcu_common(head, func, false); +} +EXPORT_SYMBOL_GPL(call_rcu_hurry); +#endif + +/** + * call_rcu() - Queue an RCU callback for invocation after a grace period. + * By default the callbacks are 'lazy' and are kept hidden from the main + * ->cblist to prevent starting of grace periods too soon. + * If you desire grace periods to start very soon, use call_rcu_hurry(). + * + * @head: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all pre-existing RCU read-side + * critical sections have completed. However, the callback function + * might well execute concurrently with RCU read-side critical sections + * that started after call_rcu() was invoked. + * + * RCU read-side critical sections are delimited by rcu_read_lock() + * and rcu_read_unlock(), and may be nested. In addition, but only in + * v5.0 and later, regions of code across which interrupts, preemption, + * or softirqs have been disabled also serve as RCU read-side critical + * sections. This includes hardware interrupt handlers, softirq handlers, + * and NMI handlers. + * + * Note that all CPUs must agree that the grace period extended beyond + * all pre-existing RCU read-side critical section. On systems with more + * than one CPU, this means that when "func()" is invoked, each CPU is + * guaranteed to have executed a full memory barrier since the end of its + * last RCU read-side critical section whose beginning preceded the call + * to call_rcu(). It also means that each CPU executing an RCU read-side + * critical section that continues beyond the start of "func()" must have + * executed a memory barrier after the call_rcu() but before the beginning + * of that RCU read-side critical section. Note that these guarantees + * include CPUs that are offline, idle, or executing in user mode, as + * well as CPUs that are executing in the kernel. + * + * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the + * resulting RCU callback function "func()", then both CPU A and CPU B are + * guaranteed to execute a full memory barrier during the time interval + * between the call to call_rcu() and the invocation of "func()" -- even + * if CPU A and CPU B are the same CPU (but again only if the system has + * more than one CPU). + * + * Implementation of these memory-ordering guarantees is described here: + * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. + */ +void call_rcu(struct rcu_head *head, rcu_callback_t func) +{ + return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY)); +} +EXPORT_SYMBOL_GPL(call_rcu);

/* Maximum number of jiffies to wait before draining a batch. */ #define KFREE_DRAIN_JIFFIES (5 * HZ) @@ -3575,7 +3612,7 @@ void synchronize_rcu(void) if (rcu_gp_is_expedited()) synchronize_rcu_expedited(); else - wait_rcu_gp(call_rcu); + wait_rcu_gp(call_rcu_hurry); return; }

@@ -3978,7 +4015,7 @@ static void rcu_barrier_entrain(struct rcu_data *rdp) * if it's fully lazy. */ was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist); - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies)); + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist); if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) { atomic_inc(&rcu_state.barrier_cpu_count); @@ -4417,7 +4454,7 @@ void rcutree_migrate_callbacks(int cpu) my_rdp = this_cpu_ptr(&rcu_data); my_rnp = my_rdp->mynode; rcu_nocb_lock(my_rdp); /* irqs already disabled. */ - WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies)); + WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false)); raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */ /* Leverage recent GPs and set GP for new callbacks. */ needwake = rcu_advance_cbs(my_rnp, rdp) || diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 43babe7b1fbf..6f63d2239946 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -262,14 +262,16 @@ struct rcu_data { unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */

+ long lazy_len; /* Length of buffered lazy callbacks. */ int cpu; };

/* Values for nocb_defer_wakeup field in struct rcu_data. */ #define RCU_NOCB_WAKE_NOT 0 #define RCU_NOCB_WAKE_BYPASS 1 -#define RCU_NOCB_WAKE 2 -#define RCU_NOCB_WAKE_FORCE 3 +#define RCU_NOCB_WAKE_LAZY 2 +#define RCU_NOCB_WAKE 3 +#define RCU_NOCB_WAKE_FORCE 4

#define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) /* For jiffies_till_first_fqs and */ @@ -444,9 +446,10 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq); static void rcu_init_one_nocb(struct rcu_node *rnp); static bool wake_nocb_gp(struct rcu_data *rdp, bool force); static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j); + unsigned long j, bool lazy); static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags); + bool *was_alldone, unsigned long flags, + bool lazy); static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, unsigned long flags); static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 75e8d9652f7b..6f69b4cc21ea 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -953,7 +953,7 @@ void synchronize_rcu_expedited(void)

/* If expedited grace periods are prohibited, fall back to normal. */ if (rcu_gp_is_normal()) { - wait_rcu_gp(call_rcu); + wait_rcu_gp(call_rcu_hurry); return; }

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index e8027f4d441c..64cddf559dd2 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -241,6 +241,31 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force) return __wake_nocb_gp(rdp_gp, rdp, force, flags); }

+/* + * LAZY_FLUSH_JIFFIES decides the maximum amount of time that + * can elapse before lazy callbacks are flushed. Lazy callbacks + * could be flushed much earlier for a number of other reasons + * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are + * left unsubmitted to RCU after those many jiffies. + */ +#define LAZY_FLUSH_JIFFIES (10 * HZ) +static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES; + +#ifdef CONFIG_RCU_LAZY +// To be called only from test code. +void rcu_lazy_set_jiffies_till_flush(unsigned long jif) +{ + jiffies_till_flush = jif; +} +EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush); + +unsigned long rcu_lazy_get_jiffies_till_flush(void) +{ + return jiffies_till_flush; +} +EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush); +#endif + /* * Arrange to wake the GP kthread for this NOCB group at some future * time when it is safe to do so. @@ -254,10 +279,14 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype, raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);

/* - * Bypass wakeup overrides previous deferments. In case - * of callback storm, no need to wake up too early. + * Bypass wakeup overrides previous deferments. In case of + * callback storms, no need to wake up too early. */ - if (waketype == RCU_NOCB_WAKE_BYPASS) { + if (waketype == RCU_NOCB_WAKE_LAZY && + rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) { + mod_timer(&rdp_gp->nocb_timer, jiffies + jiffies_till_flush); + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + } else if (waketype == RCU_NOCB_WAKE_BYPASS) { mod_timer(&rdp_gp->nocb_timer, jiffies + 2); WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); } else { @@ -278,10 +307,13 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype, * proves to be initially empty, just return false because the no-CB GP * kthread may need to be awakened in this case. * + * Return true if there was something to be flushed and it succeeded, otherwise + * false. + * * Note that this function always returns true if rhp is NULL. */ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) + unsigned long j, bool lazy) { struct rcu_cblist rcl;

@@ -295,7 +327,20 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */ if (rhp) rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ - rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp); + + /* + * If the new CB requested was a lazy one, queue it onto the main + * ->cblist so we can take advantage of a sooner grade period. + */ + if (lazy && rhp) { + rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, NULL); + rcu_cblist_enqueue(&rcl, rhp); + WRITE_ONCE(rdp->lazy_len, 0); + } else { + rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp); + WRITE_ONCE(rdp->lazy_len, 0); + } + rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl); WRITE_ONCE(rdp->nocb_bypass_first, j); rcu_nocb_bypass_unlock(rdp); @@ -311,13 +356,13 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, * Note that this function always returns true if rhp is NULL. */ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) + unsigned long j, bool lazy) { if (!rcu_rdp_is_offloaded(rdp)) return true; rcu_lockdep_assert_cblist_protected(rdp); rcu_nocb_bypass_lock(rdp); - return rcu_nocb_do_flush_bypass(rdp, rhp, j); + return rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy); }

/* @@ -330,7 +375,7 @@ static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j) if (!rcu_rdp_is_offloaded(rdp) || !rcu_nocb_bypass_trylock(rdp)) return; - WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j)); + WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false)); }

/* @@ -352,12 +397,14 @@ static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j) * there is only one CPU in operation. */ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags) + bool *was_alldone, unsigned long flags, + bool lazy) { unsigned long c; unsigned long cur_gp_seq; unsigned long j = jiffies; long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + bool bypass_is_lazy = (ncbs == READ_ONCE(rdp->lazy_len));

lockdep_assert_irqs_disabled();

@@ -402,24 +449,29 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, // If there hasn't yet been all that many ->cblist enqueues // this jiffy, tell the caller to enqueue onto ->cblist. But flush // ->nocb_bypass first. - if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) { + // Lazy CBs throttle this back and do immediate bypass queuing. + if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) { rcu_nocb_lock(rdp); *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); if (*was_alldone) trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstQ")); - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j)); + + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, false)); WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); return false; // Caller must enqueue the callback. }

// If ->nocb_bypass has been used too long or is too full, // flush ->nocb_bypass to ->cblist. - if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) || + if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) || + (ncbs && bypass_is_lazy && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush))) || ncbs >= qhimark) { rcu_nocb_lock(rdp); - if (!rcu_nocb_flush_bypass(rdp, rhp, j)) { - *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + + if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) { if (*was_alldone) trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstQ")); @@ -441,13 +493,24 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ rcu_cblist_enqueue(&rdp->nocb_bypass, rhp); + + if (lazy) + WRITE_ONCE(rdp->lazy_len, rdp->lazy_len + 1); + if (!ncbs) { WRITE_ONCE(rdp->nocb_bypass_first, j); trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ")); } rcu_nocb_bypass_unlock(rdp); smp_mb(); /* Order enqueue before wake. */ - if (ncbs) { + // A wake up of the grace period kthread or timer adjustment + // needs to be done only if: + // 1. Bypass list was fully empty before (this is the first + // bypass list entry), or: + // 2. Both of these conditions are met: + // a. The bypass list previously had only lazy CBs, and: + // b. The new CB is non-lazy. + if (ncbs && (!bypass_is_lazy || lazy)) { local_irq_restore(flags); } else { // No-CBs GP kthread might be indefinitely asleep, if so, wake. @@ -475,8 +538,10 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, unsigned long flags) __releases(rdp->nocb_lock) { + long bypass_len; unsigned long cur_gp_seq; unsigned long j; + long lazy_len; long len; struct task_struct *t;

@@ -490,9 +555,16 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, } // Need to actually to a wakeup. len = rcu_segcblist_n_cbs(&rdp->cblist); + bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_len = READ_ONCE(rdp->lazy_len); if (was_alldone) { rdp->qlen_last_fqs_check = len; - if (!irqs_disabled_flags(flags)) { + // Only lazy CBs in bypass list + if (lazy_len && bypass_len == lazy_len) { + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY, + TPS("WakeLazy")); + } else if (!irqs_disabled_flags(flags)) { /* ... if queue was empty ... */ rcu_nocb_unlock_irqrestore(rdp, flags); wake_nocb_gp(rdp, false); @@ -583,12 +655,12 @@ static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu) static void nocb_gp_wait(struct rcu_data *my_rdp) { bool bypass = false; - long bypass_ncbs; int __maybe_unused cpu = my_rdp->cpu; unsigned long cur_gp_seq; unsigned long flags; bool gotcbs = false; unsigned long j = jiffies; + bool lazy = false; bool needwait_gp = false; // This prevents actual uninitialized use. bool needwake; bool needwake_gp; @@ -618,24 +690,43 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) * won't be ignored for long. */ list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) { + long bypass_ncbs; + bool flush_bypass = false; + long lazy_ncbs; + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check")); rcu_nocb_lock_irqsave(rdp, flags); lockdep_assert_held(&rdp->nocb_lock); bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - if (bypass_ncbs && + lazy_ncbs = READ_ONCE(rdp->lazy_len); + + if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) || + bypass_ncbs > 2 * qhimark)) { + flush_bypass = true; + } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) && (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) || bypass_ncbs > 2 * qhimark)) { - // Bypass full or old, so flush it. - (void)rcu_nocb_try_flush_bypass(rdp, j); - bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + flush_bypass = true; } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) { rcu_nocb_unlock_irqrestore(rdp, flags); continue; /* No callbacks here, try next. */ } + + if (flush_bypass) { + // Bypass full or old, so flush it. + (void)rcu_nocb_try_flush_bypass(rdp, j); + bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_ncbs = READ_ONCE(rdp->lazy_len); + } + if (bypass_ncbs) { trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("Bypass")); - bypass = true; + bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass")); + if (bypass_ncbs == lazy_ncbs) + lazy = true; + else + bypass = true; } rnp = rdp->mynode;

@@ -683,12 +774,20 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) my_rdp->nocb_gp_gp = needwait_gp; my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;

- if (bypass && !rcu_nocb_poll) { - // At least one child with non-empty ->nocb_bypass, so set - // timer in order to avoid stranding its callbacks. - wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS, - TPS("WakeBypassIsDeferred")); + // At least one child with non-empty ->nocb_bypass, so set + // timer in order to avoid stranding its callbacks. + if (!rcu_nocb_poll) { + // If bypass list only has lazy CBs. Add a deferred lazy wake up. + if (lazy && !bypass) { + wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY, + TPS("WakeLazyIsDeferred")); + // Otherwise add a deferred bypass wake up. + } else if (bypass) { + wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS, + TPS("WakeBypassIsDeferred")); + } } + if (rcu_nocb_poll) { /* Polling, so trace if first poll in the series. */ if (gotcbs) @@ -1014,7 +1113,7 @@ static long rcu_nocb_rdp_deoffload(void *arg) * return false, which means that future calls to rcu_nocb_try_bypass() * will refuse to put anything into the bypass. */ - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies)); + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); /* * Start with invoking rcu_core() early. This way if the current thread * happens to preempt an ongoing call to rcu_core() in the middle, @@ -1268,6 +1367,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) raw_spin_lock_init(&rdp->nocb_gp_lock); timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); rcu_cblist_init(&rdp->nocb_bypass); + WRITE_ONCE(rdp->lazy_len, 0); mutex_init(&rdp->nocb_gp_kthread_mutex); }

@@ -1553,13 +1653,13 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force) }

static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) + unsigned long j, bool lazy) { return true; }

static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags) + bool *was_alldone, unsigned long flags, bool lazy) { return false; }

From: Hou Tao houtao1@huawei.com

commit 156c977c539e87e173f505b23989d7b0ec0bc7d8 upstream.

When "node->prefixlen == matchlen" is true, it means that the node is fully matched. If "node->prefixlen == key->prefixlen" is false, it means the prefix length of key is greater than the prefix length of node, otherwise, matchlen will not be equal with node->prefixlen. However, it also implies that the prefix length of node must be less than max_prefixlen.

Therefore, "node->prefixlen == trie->max_prefixlen" will always be false when the check of "node->prefixlen == key->prefixlen" returns false. Remove this unnecessary comparison.

Reviewed-by: Toke Høiland-Jørgensen toke@redhat.com Acked-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Hou Tao houtao1@huawei.com Link: https://lore.kernel.org/r/20241206110622.1161752-2-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- kernel/bpf/lpm_trie.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index fd6e31e72290..6c96241f49a4 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -358,8 +358,7 @@ static int trie_update_elem(struct bpf_map *map, matchlen = longest_prefix_match(trie, node, key);

if (node->prefixlen != matchlen || - node->prefixlen == key->prefixlen || - node->prefixlen == trie->max_prefixlen) + node->prefixlen == key->prefixlen) break;

next_bit = extract_bit(key->data, node->prefixlen);