[Cluster-devel] Re: [PATCH 2/2] dlm: Add down/up_write_non_owner to keep lockdep happy

[David Teigland]

On Thu, Nov 12, 2009 at 02:29:18PM +0000, Steven Whitehouse wrote:
> Hi,
> 
> On Thu, 2009-11-12 at 15:22 +0100, Ingo Molnar wrote:
> > * Steven Whitehouse <swhiteho at redhat.com> wrote:
> > 
> > > I looked at possibly changing this to use completions, but
> > > it seems that the usage here is not easily adapted to that.
> > > This patch adds suitable annotation to the write side of
> > > the ls_in_recovery semaphore so that we don't get nasty
> > > messages from lockdep when mounting a gfs2 filesystem.
> > 
> > What do those 'nasty messages' say? If they expose some bug and this
> > patch works around that bug by hiding it then NAK ...
> > 
> >         Ingo
> > 
> The nasty messages are moaning that the lock is being taken in one
> thread and unlocked in another. I couldn't see any bugs in the code when
> I looked at it. Below are the messages that I get - to reproduce just
> mount a GFS2 filesystem with the dlm lock manager. It happens on every
> mount,
> 
> Steve.
> 
> Nov 12 15:10:01 chywoon kernel:
> =============================================
> Nov 12 15:10:01 chywoon kernel: [ INFO: possible recursive locking
> detected ]

That recursive locking trace is something different.  up_write_non_owner()
addresses this trace, which as you say, is from doing the down and up from
different threads (which is the intention):

Nov 11 16:50:08 bull-02 kernel: GFS2: fsid=bull:foo.1: Joined cluster. Now mounting FS...
Nov 11 16:50:09 bull-02 kernel: 
Nov 11 16:50:09 bull-02 kernel: =====================================
Nov 11 16:50:09 bull-02 kernel: [ BUG: bad unlock balance detected! ]
Nov 11 16:50:09 bull-02 kernel: -------------------------------------
Nov 11 16:50:09 bull-02 kernel: dlm_recoverd/8958 is trying to release lock (&ls->ls_in_recovery) at:
Nov 11 16:50:09 bull-02 kernel: [<ffffffffa02e0fa7>] dlm_recoverd+0x323/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel: but there are no more locks to release!
Nov 11 16:50:09 bull-02 kernel: 
Nov 11 16:50:09 bull-02 kernel: other info that might help us debug this:
Nov 11 16:50:09 bull-02 kernel: 3 locks held by dlm_recoverd/8958:
Nov 11 16:50:09 bull-02 kernel:  #0:  (&ls->ls_recoverd_active){......}, at: [<ffffffffa02e0d74>] dlm_recoverd+0xf0/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  #1:  (&ls->ls_recv_active){......}, at: [<ffffffffa02e0f81>] dlm_recoverd+0x2fd/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  #2:  (&ls->ls_recover_lock){......}, at: [<ffffffffa02e0f89>] dlm_recoverd+0x305/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel: 
Nov 11 16:50:09 bull-02 kernel: stack backtrace:
Nov 11 16:50:09 bull-02 kernel: Pid: 8958, comm: dlm_recoverd Not tainted 2.6.32-rc5 #2
Nov 11 16:50:09 bull-02 kernel: Call Trace:
Nov 11 16:50:09 bull-02 kernel:  [<ffffffffa02e0fa7>] ? dlm_recoverd+0x323/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8106949b>] print_unlock_inbalance_bug+0xd6/0xe0
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff81069563>] lock_release_non_nested+0xbe/0x259
Nov 11 16:50:09 bull-02 kernel:  [<ffffffffa02e0fa7>] ? dlm_recoverd+0x323/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  [<ffffffffa02e0fa7>] ? dlm_recoverd+0x323/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8106b8ae>] lock_release+0x14a/0x16c
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8105fb71>] up_write+0x1e/0x2d
Nov 11 16:50:09 bull-02 kernel:  [<ffffffffa02e0fa7>] dlm_recoverd+0x323/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  [<ffffffffa02e0c84>] ? dlm_recoverd+0x0/0x4ce [dlm]
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8105cad0>] kthread+0x7d/0x85
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8100ca1a>] child_rip+0xa/0x20
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8105ca32>] ? kthreadd+0xc2/0xe3
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8105ca53>] ? kthread+0x0/0x85
Nov 11 16:50:09 bull-02 kernel:  [<ffffffff8100ca10>] ? child_rip+0x0/0x20