Patchv4 was updated based on Hailong and Uladzislau's comments, where vbq is obtained from vb->cpu, thus avoiding disabling preemption. Furthermore, Baoquan's suggestion was not adopted because it made vbq accesses completely interleaved across all CPUs, which defeats the goal of per_cpu.
On Fri, Jun 7, 2024 at 10:31 AM zhaoyang.huang zhaoyang.huang@unisoc.com wrote:
From: Zhaoyang Huang zhaoyang.huang@unisoc.com
vmalloc area runs out in our ARM64 system during an erofs test as vm_map_ram failed[1]. By following the debug log, we find that vm_map_ram()->vb_alloc() will allocate new vb->va which corresponding to 4MB vmalloc area as list_for_each_entry_rcu returns immediately when vbq->free->next points to vbq->free. That is to say, 65536 times of page fault after the list's broken will run out of the whole vmalloc area. This should be introduced by one vbq->free->next point to vbq->free which makes list_for_each_entry_rcu can not iterate the list and find the BUG.
[1] PID: 1 TASK: ffffff80802b4e00 CPU: 6 COMMAND: "init" #0 [ffffffc08006afe0] __switch_to at ffffffc08111d5cc #1 [ffffffc08006b040] __schedule at ffffffc08111dde0 #2 [ffffffc08006b0a0] schedule at ffffffc08111e294 #3 [ffffffc08006b0d0] schedule_preempt_disabled at ffffffc08111e3f0 #4 [ffffffc08006b140] __mutex_lock at ffffffc08112068c #5 [ffffffc08006b180] __mutex_lock_slowpath at ffffffc08111f8f8 #6 [ffffffc08006b1a0] mutex_lock at ffffffc08111f834 #7 [ffffffc08006b1d0] reclaim_and_purge_vmap_areas at ffffffc0803ebc3c #8 [ffffffc08006b290] alloc_vmap_area at ffffffc0803e83fc #9 [ffffffc08006b300] vm_map_ram at ffffffc0803e78c0
Fixes: fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
For detailed reason of broken list, please refer to below URL https://lore.kernel.org/all/20240531024820.5507-1-hailong.liu@oppo.com/
Suggested-by: Hailong.Liu hailong.liu@oppo.com Signed-off-by: Zhaoyang Huang zhaoyang.huang@unisoc.com
v2: introduce cpu in vmap_block to record the right CPU number v3: use get_cpu/put_cpu to prevent schedule between core v4: replace get_cpu/put_cpu by another API to avoid disabling preemption
mm/vmalloc.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 22aa63f4ef63..89eb034f4ac6 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2458,6 +2458,7 @@ struct vmap_block { struct list_head free_list; struct rcu_head rcu_head; struct list_head purge;
unsigned int cpu;};
/* Queue of free and dirty vmap blocks, for allocation and flushing purposes */ @@ -2585,8 +2586,15 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) free_vmap_area(va); return ERR_PTR(err); }
vbq = raw_cpu_ptr(&vmap_block_queue);
/** list_add_tail_rcu could happened in another core* rather than vb->cpu due to task migration, which* is safe as list_add_tail_rcu will ensure the list's* integrity together with list_for_each_rcu from read* side.*/vb->cpu = raw_smp_processor_id();vbq = per_cpu_ptr(&vmap_block_queue, vb->cpu); spin_lock(&vbq->lock); list_add_tail_rcu(&vb->free_list, &vbq->free); spin_unlock(&vbq->lock);@@ -2614,9 +2622,10 @@ static void free_vmap_block(struct vmap_block *vb) }
static bool purge_fragmented_block(struct vmap_block *vb,
struct vmap_block_queue *vbq, struct list_head *purge_list,bool force_purge)
struct list_head *purge_list, bool force_purge){
struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, vb->cpu);if (vb->free + vb->dirty != VMAP_BBMAP_BITS || vb->dirty == VMAP_BBMAP_BITS) return false;@@ -2664,7 +2673,7 @@ static void purge_fragmented_blocks(int cpu) continue;
spin_lock(&vb->lock);
purge_fragmented_block(vb, vbq, &purge, true);
purge_fragmented_block(vb, &purge, true); spin_unlock(&vb->lock); } rcu_read_unlock();@@ -2801,7 +2810,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush) * not purgeable, check whether there is dirty * space to be flushed. */
if (!purge_fragmented_block(vb, vbq, &purge_list, false) &&
if (!purge_fragmented_block(vb, &purge_list, false) && vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) { unsigned long va_start = vb->va->va_start; unsigned long s, e;-- 2.25.1