[ 006/175] staging: zcache: avoid AB-BA deadlock condition
From: Greg KH <gregkh@linuxfoundation.org>
Date: 2012-03-30 21:17:02
Also in:
lkml
3.3-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andrea Righi <redacted>
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 <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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);