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mm/zsmalloc: fix release order of locks in zs_page_migrate()

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In zs_page_migrate(), locks are acquired in the following order:
  1. write_lock(&pool->lock)
  2. spin_lock(&class->lock)
  3. zspage_write_trylock(zspage)

However, upon successful page migration, they were being released in
forward acquisition (FIFO) order:
  1. write_unlock(&pool->lock)
  2. spin_unlock(&class->lock)
  3. zspage_write_unlock(zspage)

Fix the unlocking order to release locks in strict reverse (LIFO)
order of acquisition:
  3. zspage_write_unlock(zspage)
  2. spin_unlock(&class->lock)
  1. write_unlock(&pool->lock)

Releasing locks in reverse order of acquisition adheres to standard
kernel locking hygiene, prevents potential lock ordering and lockdep
inconsistencies.

Link: https://lore.kernel.org/20260728055333.421080-1-richardycc@google.com
Signed-off-by: Richard Chang <richardycc@google.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Tested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Martin Liu <liumartin@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Richard Chang 2026-07-28 05:53:33 +00:00 committed by Andrew Morton
parent 2f99b6fe0b
commit f276408a81
1 changed files with 2 additions and 2 deletions
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4
mm/zsmalloc.c
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@ -1926,9 +1926,9 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
* Since we complete the data copy and set up new zspage structure,
* it's okay to release migration_lock.
*/
write_unlock(&pool->lock);
spin_unlock(&class->lock);
zspage_write_unlock(zspage);
spin_unlock(&class->lock);
write_unlock(&pool->lock);
zpdesc_get(newzpdesc);
if (zpdesc_zone(newzpdesc) != zpdesc_zone(zpdesc)) {