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From: Sage Weil <sage@newdream.net>
To: linux-btrfs@vger.kernel.org
Cc: Sage Weil <sage@newdream.net>
Subject: [PATCH 1/6] Btrfs: fix deadlock in btrfs_commit_transaction
Date: Mon, 25 Oct 2010 12:07:37 -0700	[thread overview]
Message-ID: <1288033662-21464-2-git-send-email-sage@newdream.net> (raw)
In-Reply-To: <1288033662-21464-1-git-send-email-sage@newdream.net>

We calculate timeout (either 1 or MAX_SCHEDULE_TIMEOUT) based on whether
num_writers > 1 or should_grow at the top of the loop.  Then, much much
later, we wait for that timeout if either num_writers or should_grow is
true.  However, it's possible for a racing process (calling
btrfs_end_transaction()) to decrement num_writers such that we wait
forever instead of for 1.

Fix this by deciding how long to wait when we wait.

Signed-off-by: Sage Weil <sage@newdream.net>
---
 fs/btrfs/transaction.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 66e4c66..bf399ea 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -992,7 +992,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
 	unsigned long joined = 0;
-	unsigned long timeout = 1;
 	struct btrfs_transaction *cur_trans;
 	struct btrfs_transaction *prev_trans = NULL;
 	DEFINE_WAIT(wait);
@@ -1063,11 +1062,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			snap_pending = 1;
 
 		WARN_ON(cur_trans != trans->transaction);
-		if (cur_trans->num_writers > 1)
-			timeout = MAX_SCHEDULE_TIMEOUT;
-		else if (should_grow)
-			timeout = 1;
-
 		mutex_unlock(&root->fs_info->trans_mutex);
 
 		if (flush_on_commit || snap_pending) {
@@ -1089,8 +1083,10 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 				TASK_UNINTERRUPTIBLE);
 
 		smp_mb();
-		if (cur_trans->num_writers > 1 || should_grow)
-			schedule_timeout(timeout);
+		if (cur_trans->num_writers > 1)
+			schedule_timeout(MAX_SCHEDULE_TIMEOUT);
+		else if (should_grow)
+			schedule_timeout(1);
 
 		mutex_lock(&root->fs_info->trans_mutex);
 		finish_wait(&cur_trans->writer_wait, &wait);
-- 
1.6.6.1


  reply	other threads:[~2010-10-25 19:07 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-10-25 19:07 [PATCH 0/6] Btrfs commit fixes, async subvol operations Sage Weil
2010-10-25 19:07 ` Sage Weil [this message]
2010-10-25 19:07   ` [PATCH 2/6] Btrfs: async transaction commit Sage Weil
2010-10-25 19:07     ` [PATCH 3/6] Btrfs: add START_SYNC, WAIT_SYNC ioctls Sage Weil
2010-10-25 19:07       ` [PATCH 4/6] Btrfs: add SNAP_CREATE_ASYNC ioctl Sage Weil
2010-10-25 19:07         ` [PATCH 5/6] Btrfs: make SNAP_DESTROY async Sage Weil
2010-10-25 19:07           ` [PATCH 6/6] Btrfs: allow subvol deletion by owner Sage Weil
2010-10-26  6:46   ` [PATCH 1/6] Btrfs: fix deadlock in btrfs_commit_transaction liubo
2010-10-26 16:36     ` Sage Weil
2010-10-26 17:06       ` Chris Mason
2010-10-27  0:41         ` liubo
2010-10-25 19:29 ` [PATCH 0/6] Btrfs commit fixes, async subvol operations Chris Mason
2010-10-25 19:41   ` Sage Weil
2010-10-25 19:58     ` Chris Mason
2010-10-25 21:27       ` Sage Weil

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