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staging: zcache: avoid AB-BA deadlock condition

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commit cfbc6a9221 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 <andrea@betterlinux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andrea Righi 2012-02-20 13:11:49 +01:00 committed by Greg Kroah-Hartman
parent dc8e82a35a
commit 7e6373b366
1 changed files with 2 additions and 2 deletions
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4
drivers/staging/zcache/zcache-main.c
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@ -299,10 +299,12 @@ static void zbud_free_and_delist(struct zbud_hdr *zh)
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 zbud_hdr *zh)
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_hdr *zh)
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);