From 88ca9f019597f85dacdeca9df1a94be59a595e6b Mon Sep 17 00:00:00 2001 From: Miaohe Lin Date: Fri, 29 Apr 2022 14:40:43 +0800 Subject: [PATCH] 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: 594060dd2247 ("z3fold: stricter locking and more careful reclaim") Signed-off-by: Miaohe Lin Reviewed-by: Vitaly Wool Signed-off-by: Andrew Morton --- mm/z3fold.c | 18 +++--------------- 1 file changed, 3 insertions(+), 15 deletions(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 4a3cd2ff15b05..a7769befd74ef 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; } -- 2.39.5