6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra peterz@infradead.org
[ Upstream commit d16317de9b412aa7bd3598c607112298e36b4352 ]
The read side of seqcount_latch consists of:
do { seq = raw_read_seqcount_latch(&latch->seq); ... } while (read_seqcount_latch_retry(&latch->seq, seq));
which is asymmetric in the raw_ department, and sure enough, read_seqcount_latch_retry() includes (explicit) instrumentation where raw_read_seqcount_latch() does not.
This inconsistency becomes a problem when trying to use it from noinstr code. As such, fix it by renaming and re-implementing raw_read_seqcount_latch_retry() without the instrumentation.
Specifically the instrumentation in question is kcsan_atomic_next(0) in do___read_seqcount_retry(). Loosing this annotation is not a problem because raw_read_seqcount_latch() does not pass through kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX).
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Petr Mladek pmladek@suse.com Tested-by: Michael Kelley mikelley@microsoft.com # Hyper-V Link: https://lore.kernel.org/r/20230519102715.233598176@infradead.org Stable-dep-of: 5c1806c41ce0 ("kcsan, seqlock: Support seqcount_latch_t") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/rbtree_latch.h | 2 +- include/linux/seqlock.h | 15 ++++++++------- kernel/printk/printk.c | 2 +- kernel/time/sched_clock.c | 2 +- kernel/time/timekeeping.c | 4 ++-- 5 files changed, 13 insertions(+), 12 deletions(-)
diff --git a/include/linux/rbtree_latch.h b/include/linux/rbtree_latch.h index 3d1a9e716b803..6a0999c26c7cf 100644 --- a/include/linux/rbtree_latch.h +++ b/include/linux/rbtree_latch.h @@ -206,7 +206,7 @@ latch_tree_find(void *key, struct latch_tree_root *root, do { seq = raw_read_seqcount_latch(&root->seq); node = __lt_find(key, root, seq & 1, ops->comp); - } while (read_seqcount_latch_retry(&root->seq, seq)); + } while (raw_read_seqcount_latch_retry(&root->seq, seq));
return node; } diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index d778af83c8f36..e9bd2f65d7f4e 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -671,9 +671,9 @@ typedef struct { * * Return: sequence counter raw value. Use the lowest bit as an index for * picking which data copy to read. The full counter must then be checked - * with read_seqcount_latch_retry(). + * with raw_read_seqcount_latch_retry(). */ -static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) +static __always_inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) { /* * Pairs with the first smp_wmb() in raw_write_seqcount_latch(). @@ -683,16 +683,17 @@ static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) }
/** - * read_seqcount_latch_retry() - end a seqcount_latch_t read section + * raw_read_seqcount_latch_retry() - end a seqcount_latch_t read section * @s: Pointer to seqcount_latch_t * @start: count, from raw_read_seqcount_latch() * * Return: true if a read section retry is required, else false */ -static inline int -read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) +static __always_inline int +raw_read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) { - return read_seqcount_retry(&s->seqcount, start); + smp_rmb(); + return unlikely(READ_ONCE(s->seqcount.sequence) != start); }
/** @@ -752,7 +753,7 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) * entry = data_query(latch->data[idx], ...); * * // This includes needed smp_rmb() - * } while (read_seqcount_latch_retry(&latch->seq, seq)); + * } while (raw_read_seqcount_latch_retry(&latch->seq, seq)); * * return entry; * } diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 0ae06d5046bb0..5a88134fba79f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -457,7 +457,7 @@ static u64 latched_seq_read_nolock(struct latched_seq *ls) seq = raw_read_seqcount_latch(&ls->latch); idx = seq & 0x1; val = ls->val[idx]; - } while (read_seqcount_latch_retry(&ls->latch, seq)); + } while (raw_read_seqcount_latch_retry(&ls->latch, seq));
return val; } diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index 8464c5acc9133..e8f2fb09a214d 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -77,7 +77,7 @@ notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
notrace int sched_clock_read_retry(unsigned int seq) { - return read_seqcount_latch_retry(&cd.seq, seq); + return raw_read_seqcount_latch_retry(&cd.seq, seq); }
unsigned long long notrace sched_clock(void) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 8ac43afc11f96..dd294e96193be 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -450,7 +450,7 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) tkr = tkf->base + (seq & 0x01); now = ktime_to_ns(tkr->base); now += fast_tk_get_delta_ns(tkr); - } while (read_seqcount_latch_retry(&tkf->seq, seq)); + } while (raw_read_seqcount_latch_retry(&tkf->seq, seq));
return now; } @@ -566,7 +566,7 @@ static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono) basem = ktime_to_ns(tkr->base); baser = ktime_to_ns(tkr->base_real); delta = fast_tk_get_delta_ns(tkr); - } while (read_seqcount_latch_retry(&tkf->seq, seq)); + } while (raw_read_seqcount_latch_retry(&tkf->seq, seq));
if (mono) *mono = basem + delta;