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[PATCH] Btrfs: fix lockdep error in async commit

To: linux-btrfs@xxxxxxxxxxxxxxx
Subject: [PATCH] Btrfs: fix lockdep error in async commit
From: Liu Bo <bo.li.liu@xxxxxxxxxx>
Date: Wed, 6 Nov 2013 16:57:55 +0800
Cc: xfs@xxxxxxxxxxx, Miao Xie <miaox@xxxxxxxxxxxxxx>, <majianpeng@xxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
Lockdep complains about btrfs's async commit:

[ 2372.462171] [ BUG: bad unlock balance detected! ]
[ 2372.462191] 3.12.0+ #32 Tainted: G        W
[ 2372.462209] -------------------------------------
[ 2372.462228] ceph-osd/14048 is trying to release lock (sb_internal) at:
[ 2372.462275] [<ffffffffa022cb10>] btrfs_commit_transaction_async+0x1b0/0x2a0 
[btrfs]
[ 2372.462305] but there are no more locks to release!
[ 2372.462324]
[ 2372.462324] other info that might help us debug this:
[ 2372.462349] no locks held by ceph-osd/14048.
[ 2372.462367]
[ 2372.462367] stack backtrace:
[ 2372.462386] CPU: 2 PID: 14048 Comm: ceph-osd Tainted: G        W    3.12.0+ 
#32
[ 2372.462414] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To 
be filled by O.E.M., BIOS 080015  11/09/2011
[ 2372.462455]  ffffffffa022cb10 ffff88007490fd28 ffffffff816f094a 
ffff8800378aa320
[ 2372.462491]  ffff88007490fd50 ffffffff810adf4c ffff8800378aa320 
ffff88009af97650
[ 2372.462526]  ffffffffa022cb10 ffff88007490fd88 ffffffff810b01ee 
ffff8800898c0000
[ 2372.462562] Call Trace:
[ 2372.462584]  [<ffffffffa022cb10>] ? 
btrfs_commit_transaction_async+0x1b0/0x2a0 [btrfs]
[ 2372.462619]  [<ffffffff816f094a>] dump_stack+0x45/0x56
[ 2372.462642]  [<ffffffff810adf4c>] print_unlock_imbalance_bug+0xec/0x100
[ 2372.462677]  [<ffffffffa022cb10>] ? 
btrfs_commit_transaction_async+0x1b0/0x2a0 [btrfs]
[ 2372.462710]  [<ffffffff810b01ee>] lock_release+0x18e/0x210
[ 2372.462742]  [<ffffffffa022cb36>] btrfs_commit_transaction_async+0x1d6/0x2a0 
[btrfs]
[ 2372.462783]  [<ffffffffa025a7ce>] btrfs_ioctl_start_sync+0x3e/0xc0 [btrfs]
[ 2372.462822]  [<ffffffffa025f1d3>] btrfs_ioctl+0x4c3/0x1f70 [btrfs]
[ 2372.462849]  [<ffffffff812c0321>] ? avc_has_perm+0x121/0x1b0
[ 2372.462873]  [<ffffffff812c0224>] ? avc_has_perm+0x24/0x1b0
[ 2372.462897]  [<ffffffff8107ecc8>] ? sched_clock_cpu+0xa8/0x100
[ 2372.462922]  [<ffffffff8117b145>] do_vfs_ioctl+0x2e5/0x4e0
[ 2372.462946]  [<ffffffff812c19e6>] ? file_has_perm+0x86/0xa0
[ 2372.462969]  [<ffffffff8117b3c1>] SyS_ioctl+0x81/0xa0
[ 2372.462991]  [<ffffffff817045a4>] tracesys+0xdd/0xe2
====================================================

It's because that we don't do the right thing when checking if it's ok to
tell lockdep that we're trying to release the rwsem.

If the trans handle's type is TRANS_ATTACH, we won't acquire the freeze rwsem, 
but
as TRANS_ATTACH fits the check (trans < TRANS_JOIN_NOLOCK), we'll release the 
freeze
rwsem, which makes lockdep complains a lot.

Reported-by: Ma Jianpeng <majianpeng@xxxxxxxxx>
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx>
---
 fs/btrfs/transaction.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 8c81bdc..c094f08 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1453,7 +1453,7 @@ static void do_async_commit(struct work_struct *work)
         * We've got freeze protection passed with the transaction.
         * Tell lockdep about it.
         */
-       if (ac->newtrans->type < TRANS_JOIN_NOLOCK)
+       if (ac->newtrans->type & __TRANS_FREEZABLE)
                rwsem_acquire_read(
                     &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
                     0, 1, _THIS_IP_);
@@ -1494,7 +1494,7 @@ int btrfs_commit_transaction_async(struct 
btrfs_trans_handle *trans,
         * Tell lockdep we've released the freeze rwsem, since the
         * async commit thread will be the one to unlock it.
         */
-       if (trans->type < TRANS_JOIN_NOLOCK)
+       if (ac->newtrans->type & __TRANS_FREEZABLE)
                rwsem_release(
                        &root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
                        1, _THIS_IP_);
-- 
1.8.1.4

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