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authorMiaohe Lin <linmiaohe@huawei.com>2021-11-05 13:45:03 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-06 13:30:43 -0700
commitafe8605ca45424629fdddfd85984b442c763dc47 (patch)
treef2c1c82517c75a7d2e0f619a7027475553d81afb /mm
parent3d88705c10677d1fc3f14786361aee649839aa7e (diff)
mm/zsmalloc.c: close race window between zs_pool_dec_isolated() and zs_unregister_migration()
There is one possible race window between zs_pool_dec_isolated() and zs_unregister_migration() because wait_for_isolated_drain() checks the isolated count without holding class->lock and there is no order inside zs_pool_dec_isolated(). Thus the below race window could be possible: zs_pool_dec_isolated zs_unregister_migration check pool->destroying != 0 pool->destroying = true; smp_mb(); wait_for_isolated_drain() wait for pool->isolated_pages == 0 atomic_long_dec(&pool->isolated_pages); atomic_long_read(&pool->isolated_pages) == 0 Since we observe the pool->destroying (false) before atomic_long_dec() for pool->isolated_pages, waking pool->migration_wait up is missed. Fix this by ensure checking pool->destroying happens after the atomic_long_dec(&pool->isolated_pages). Link: https://lkml.kernel.org/r/20210708115027.7557-1-linmiaohe@huawei.com Fixes: 701d678599d0 ("mm/zsmalloc.c: fix race condition in zs_destroy_pool") Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Henry Burns <henryburns@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/zsmalloc.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 68e8831068f4..b897ce3b399a 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1830,10 +1830,11 @@ static inline void zs_pool_dec_isolated(struct zs_pool *pool)
VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0);
atomic_long_dec(&pool->isolated_pages);
/*
- * There's no possibility of racing, since wait_for_isolated_drain()
- * checks the isolated count under &class->lock after enqueuing
- * on migration_wait.
+ * Checking pool->destroying must happen after atomic_long_dec()
+ * for pool->isolated_pages above. Paired with the smp_mb() in
+ * zs_unregister_migration().
*/
+ smp_mb__after_atomic();
if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying)
wake_up_all(&pool->migration_wait);
}