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Commit cfbc6a92 authored by Andrea Righi's avatar Andrea Righi Committed by Greg Kroah-Hartman
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staging: zcache: avoid AB-BA deadlock condition 



Commit 9256a478 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: default avatarAndrea Righi <andrea@betterlinux.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fc7e2a57

drivers/staging/zcache/zcache-main.c

+2 −2
Original line number Diff line number Diff line
@@ -333,10 +333,12 @@ 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);
@@ -344,7 +346,6 @@ 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--;
@@ -352,7 +353,6 @@ 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);