Re: writeback: bad unlock balance detected in 3.5-rc1

[Jan Kara <jack@suse.cz>]

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On Fri 08-06-12 10:36:13, Ted Tso wrote:
> 
> I can reproduce this fairly easily by using ext4 w/o a journal, running
> under KVM with 1024megs memory, with fsstress (xfstests #13):
  Argh, I wonder how come I didn't hit this. Does attached patch fix the
problem?

								Honza

> 
> 013	[   45.152457] 
> [   45.153294] =====================================
> [   45.154784] [ BUG: bad unlock balance detected! ]
> [   45.155591] 3.5.0-rc1-00002-gb22b1f1 #124 Not tainted
> [   45.155591] -------------------------------------
> [   45.155591] flush-254:16/2499 is trying to release lock (&(&wb->list_lock)->rlock) at:
> [   45.155591] [<c022c3da>] writeback_sb_inodes+0x160/0x327
> [   45.155591] but there are no more locks to release!
> [   45.155591] 
> [   45.155591] other info that might help us debug this:
> [   45.155591] 1 lock held by flush-254:16/2499:
> [   45.155591]  #0:  (&sb->s_type->i_lock_key#13){+.+...}, at: [<c022c33d>] writeback_sb_inodes+0xc3/0x327
> [   45.155591] 
> [   45.155591] stack backtrace:
> [   45.155591] Pid: 2499, comm: flush-254:16 Not tainted 3.5.0-rc1-00002-gb22b1f1 #124
> [   45.155591] Call Trace:
> [   45.155591]  [<c022c3da>] ? writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c019930e>] print_unlock_inbalance_bug+0xb4/0xc1
> [   45.155591]  [<c022c3da>] ? writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c022c3da>] ? writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c019b5c2>] lock_release_non_nested+0x9f/0x1e8
> [   45.155591]  [<c022c3da>] ? writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c022c3da>] ? writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c019b875>] lock_release+0x16a/0x18a
> [   45.155591]  [<c06ec713>] _raw_spin_unlock+0x1b/0x25
> [   45.155591]  [<c022c3da>] writeback_sb_inodes+0x160/0x327
> [   45.155591]  [<c022c784>] wb_writeback+0xf2/0x1c1
> [   45.155591]  [<c0160477>] ? _local_bh_enable_ip+0x9d/0xa6
> [   45.155591]  [<c022c8c4>] wb_do_writeback+0x71/0x18c
> [   45.155591]  [<c022ca7b>] bdi_writeback_thread+0x9c/0x18d
> [   45.155591]  [<c0199b97>] ? trace_hardirqs_on+0xb/0xd
> [   45.155591]  [<c022c9df>] ? wb_do_writeback+0x18c/0x18c
> [   45.155591]  [<c017316a>] kthread+0x6c/0x71
> [   45.155591]  [<c01730fe>] ? __init_kthread_worker+0x47/0x47
> [   45.155591]  [<c06f237a>] kernel_thread_helper+0x6/0x10
> [  105.196666] INFO: rcu_sched self-detected stall on CPU { 1}  (t=18000 jiffies)
> [  105.196670] Pid: 2499, comm: flush-254:16 Not tainted 3.5.0-rc1-00002-gb22b1f1 #124
> [  105.199991] INFO: rcu_sched self-detected stall on CPU { 0}  (t=18000 jiffies)
> --
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-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8d2fb8c..41a3ccf 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -664,6 +664,7 @@ static long writeback_sb_inodes(struct super_block *sb,
 			/* Wait for I_SYNC. This function drops i_lock... */
 			inode_sleep_on_writeback(inode);
 			/* Inode may be gone, start again */
+			spin_lock(&wb->list_lock);
 			continue;
 		}
 		inode->i_state |= I_SYNC;