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| author | Miaohe Lin <linmiaohe@huawei.com> | 2022-04-29 14:40:43 +0800 |
|---|---|---|
| committer | akpm <akpm@linux-foundation.org> | 2022-05-27 09:33:44 -0700 |
| commit | 04094226d6ce8c0cb590891e13872109aa6722f1 (patch) | |
| tree | 02723a23b7785dff1502ea3335bd6560fe76dcb0 /mm/z3fold.c | |
| parent | 4a1c3839108afcfec02f4d62d6862b2451b442ab (diff) | |
| download | lwn-04094226d6ce8c0cb590891e13872109aa6722f1.tar.gz lwn-04094226d6ce8c0cb590891e13872109aa6722f1.zip | |
mm/z3fold: fix z3fold_reclaim_page races with z3fold_free
Think about the below scenario:
CPU1 CPU2
z3fold_reclaim_page z3fold_free
spin_lock(&pool->lock) get_z3fold_header -- hold page_lock
kref_get_unless_zero
kref_put--zhdr->refcount can be 1 now
!z3fold_page_trylock
kref_put -- zhdr->refcount is 0 now
release_z3fold_page
WARN_ON(!list_empty(&zhdr->buddy)); -- we're on buddy now!
spin_lock(&pool->lock); -- deadlock here!
z3fold_reclaim_page might race with z3fold_free and will lead to pool lock
deadlock and zhdr buddy non-empty warning. To fix this, defer getting the
refcount until page_lock is held just like what __z3fold_alloc does. Note
this has the side effect that we won't break the reclaim if we meet a soon
to be released z3fold page now.
Link: https://lkml.kernel.org/r/20220429064051.61552-9-linmiaohe@huawei.com
Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/z3fold.c')
| -rw-r--r-- | mm/z3fold.c | 18 |
1 files changed, 3 insertions, 15 deletions
diff --git a/mm/z3fold.c b/mm/z3fold.c index 4a3cd2ff15b0..a7769befd74e 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -519,13 +519,6 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked) atomic64_dec(&pool->pages_nr); } -static void release_z3fold_page(struct kref *ref) -{ - struct z3fold_header *zhdr = container_of(ref, struct z3fold_header, - refcount); - __release_z3fold_page(zhdr, false); -} - static void release_z3fold_page_locked(struct kref *ref) { struct z3fold_header *zhdr = container_of(ref, struct z3fold_header, @@ -1317,12 +1310,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) break; } - if (kref_get_unless_zero(&zhdr->refcount) == 0) { - zhdr = NULL; - break; - } if (!z3fold_page_trylock(zhdr)) { - kref_put(&zhdr->refcount, release_z3fold_page); zhdr = NULL; continue; /* can't evict at this point */ } @@ -1333,14 +1321,14 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) */ if (zhdr->foreign_handles || test_and_set_bit(PAGE_CLAIMED, &page->private)) { - if (!kref_put(&zhdr->refcount, - release_z3fold_page_locked)) - z3fold_page_unlock(zhdr); + z3fold_page_unlock(zhdr); zhdr = NULL; continue; /* can't evict such page */ } list_del_init(&zhdr->buddy); zhdr->cpu = -1; + /* See comment in __z3fold_alloc. */ + kref_get(&zhdr->refcount); break; } |