This is a note to let you know that I've just added the patch titled
Btrfs: fix deadlock with nested trans handles
to the 3.14-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:
btrfs-fix-deadlock-with-nested-trans-handles.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 3bbb24b20a8800158c33eca8564f432dd14d0bf3 Mon Sep 17 00:00:00 2001
From: Josef Bacik <jbacik@xxxxxx>
Date: Thu, 6 Mar 2014 19:01:07 -0500
Subject: Btrfs: fix deadlock with nested trans handles
From: Josef Bacik <jbacik@xxxxxx>
commit 3bbb24b20a8800158c33eca8564f432dd14d0bf3 upstream.
Zach found this deadlock that would happen like this
btrfs_end_transaction <- reduce trans->use_count to 0
btrfs_run_delayed_refs
btrfs_cow_block
find_free_extent
btrfs_start_transaction <- increase trans->use_count to 1
allocate chunk
btrfs_end_transaction <- decrease trans->use_count to 0
btrfs_run_delayed_refs
lock tree block we are cowing above ^^
We need to only decrease trans->use_count if it is above 1, otherwise leave it
alone. This will make nested trans be the only ones who decrease their added
ref, and will let us get rid of the trans->use_count++ hack if we have to commit
the transaction. Thanks,
Reported-by: Zach Brown <zab@xxxxxxxxxx>
Signed-off-by: Josef Bacik <jbacik@xxxxxx>
Tested-by: Zach Brown <zab@xxxxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/transaction.c | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -683,7 +683,8 @@ static int __btrfs_end_transaction(struc
int lock = (trans->type != TRANS_JOIN_NOLOCK);
int err = 0;
- if (--trans->use_count) {
+ if (trans->use_count > 1) {
+ trans->use_count--;
trans->block_rsv = trans->orig_rsv;
return 0;
}
@@ -731,17 +732,10 @@ static int __btrfs_end_transaction(struc
}
if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
- if (throttle) {
- /*
- * We may race with somebody else here so end up having
- * to call end_transaction on ourselves again, so inc
- * our use_count.
- */
- trans->use_count++;
+ if (throttle)
return btrfs_commit_transaction(trans, root);
- } else {
+ else
wake_up_process(info->transaction_kthread);
- }
}
if (trans->type & __TRANS_FREEZABLE)
Patches currently in stable-queue which might be from jbacik@xxxxxx are
queue-3.14/btrfs-skip-submitting-barrier-for-missing-device.patch
queue-3.14/btrfs-check-for-an-extent_op-on-the-locked-ref.patch
queue-3.14/btrfs-fix-deadlock-with-nested-trans-handles.patch
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