diff options
| author | Kairui Song <kasong@tencent.com> | 2025-09-17 00:00:50 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-09-21 14:22:23 -0700 |
| commit | ae38eb210590ed69fa4f70f29959df76a4bdc4da (patch) | |
| tree | 8d3abca24e1f14c7ac43069a4a65dbe80911ecdd /mm/swap_state.c | |
| parent | 3518b931df0cc57b1b97e5c3a307ad7d5fe17650 (diff) | |
mm, swap: always lock and check the swap cache folio before use
Swap cache lookup only increases the reference count of the returned
folio. That's not enough to ensure a folio is stable in the swap cache,
so the folio could be removed from the swap cache at any time. The caller
should always lock and check the folio before using it.
We have just documented this in kerneldoc, now introduce a helper for swap
cache folio verification with proper sanity checks.
Also, sanitize a few current users to use this convention and the new
helper for easier debugging. They were not having observable problems
yet, only trivial issues like wasted CPU cycles on swapoff or reclaiming.
They would fail in some other way, but it is still better to always follow
this convention to make things robust and make later commits easier to do.
Link: https://lkml.kernel.org/r/20250916160100.31545-6-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Chris Li <chrisl@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
| -rw-r--r-- | mm/swap_state.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c index 68ec531d0f2b..9225d6b695ad 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -79,7 +79,7 @@ void show_swap_cache_info(void) * with reference count or locks. * Return: Returns the found folio on success, NULL otherwise. The caller * must lock and check if the folio still matches the swap entry before - * use. + * use (e.g. with folio_matches_swap_entry). */ struct folio *swap_cache_get_folio(swp_entry_t entry) { @@ -346,7 +346,10 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, for (;;) { int err; - /* Check the swap cache in case the folio is already there */ + /* + * Check the swap cache first, if a cached folio is found, + * return it unlocked. The caller will lock and check it. + */ folio = swap_cache_get_folio(entry); if (folio) goto got_folio; |