This is a note to let you know that I've just added the patch titled
staging: zcache: avoid AB-BA deadlock condition
to the 3.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
staging-zcache-avoid-ab-ba-deadlock-condition.patch
and it can be found in the queue-3.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From cfbc6a92212e74b07aa76c9e2f20c542e36077fb Mon Sep 17 00:00:00 2001
From: Andrea Righi <[email protected]>
Date: Mon, 20 Feb 2012 13:11:49 +0100
Subject: staging: zcache: avoid AB-BA deadlock condition
From: Andrea Righi <[email protected]>
commit cfbc6a92212e74b07aa76c9e2f20c542e36077fb upstream.
Commit 9256a47 fixed a deadlock condition, being sure that the buddy
list spinlock is always taken before the page spinlock.
However in zbud_free_and_delist() locking order is the opposite
(page lock -> list lock).
Possible unsafe locking scenario (reported by lockdep):
CPU0 CPU1
---- ----
lock(&(&zbpg->lock)->rlock);
lock(zbud_budlists_spinlock);
lock(&(&zbpg->lock)->rlock);
lock(zbud_budlists_spinlock);
Fix by grabbing the locks in opposite order in zbud_free_and_delist().
Signed-off-by: Andrea Righi <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/staging/zcache/zcache-main.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -299,10 +299,12 @@ static void zbud_free_and_delist(struct
struct zbud_page *zbpg =
container_of(zh, struct zbud_page, buddy[budnum]);
+ spin_lock(&zbud_budlists_spinlock);
spin_lock(&zbpg->lock);
if (list_empty(&zbpg->bud_list)) {
/* ignore zombie page... see zbud_evict_pages() */
spin_unlock(&zbpg->lock);
+ spin_unlock(&zbud_budlists_spinlock);
return;
}
size = zbud_free(zh);
@@ -310,7 +312,6 @@ static void zbud_free_and_delist(struct
zh_other = &zbpg->buddy[(budnum == 0) ? 1 : 0];
if (zh_other->size == 0) { /* was unbuddied: unlist and free */
chunks = zbud_size_to_chunks(size) ;
- spin_lock(&zbud_budlists_spinlock);
BUG_ON(list_empty(&zbud_unbuddied[chunks].list));
list_del_init(&zbpg->bud_list);
zbud_unbuddied[chunks].count--;
@@ -318,7 +319,6 @@ static void zbud_free_and_delist(struct
zbud_free_raw_page(zbpg);
} else { /* was buddied: move remaining buddy to unbuddied list */
chunks = zbud_size_to_chunks(zh_other->size) ;
- spin_lock(&zbud_budlists_spinlock);
list_del_init(&zbpg->bud_list);
zcache_zbud_buddied_count--;
list_add_tail(&zbpg->bud_list, &zbud_unbuddied[chunks].list);
Patches currently in stable-queue which might be from [email protected] are
queue-3.2/staging-zcache-avoid-ab-ba-deadlock-condition.patch
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