Think about the below scene:
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.
Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
mm/z3fold.c | 18 +++---------------
1 file 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;
}
--
2.23.0
