linux-kernel - Re: [2.6.20] BUG: workqueue leaked lock

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Message-ID: <17918.11420.155569.991473@notabene.brown>
Date:	Mon, 19 Mar 2007 17:24:28 +1100
From:	Neil Brown <neilb@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Folkert van Heusden <folkert@...heusden.com>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [2.6.20] BUG: workqueue leaked lock

On Friday March 16, akpm@...ux-foundation.org wrote:
> 
> OK.  That's not necessarily a bug: one could envisage a (weird) piece of
> code which takes a lock then releases it on a later workqueue invokation. 
> But I'm not sure that nfs4_laundromat() is actually supposed to be doing
> anything like that.
> 
> Then again, maybe it is: it seems to be waddling through a directory under
> the control of a little state machine, with timeouts.
> 
> Neil: help?

I'm quite certain that laundromat_main does *not* leave client_mutex
locked as the last thing it does is call nfs4_unlock_state which is
	mutex_unlock(&client_mutex);
To me, that raises some doubt about whether the lock leak check is
working properly...
It is somewhat harder to track locking of i_mutex, but it seems to me
that every time it is taken, it is released again shortly afterwards.

So I think this must be a problem with leak detection, not with NFSd.

NeilBrown


> On Fri, 16 Mar 2007 09:41:20 +0100 Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Thu, 2007-03-15 at 11:06 -0800, Andrew Morton wrote:
> > > > On Tue, 13 Mar 2007 17:50:14 +0100 Folkert van Heusden <folkert@...heusden.com> wrote:
> > > > ...
> > > > [ 1756.728209] BUG: workqueue leaked lock or atomic: nfsd4/0x00000000/3577
> > > > [ 1756.728271]     last function: laundromat_main+0x0/0x69 [nfsd]
> > > > [ 1756.728392] 2 locks held by nfsd4/3577:
> > > > [ 1756.728435]  #0:  (client_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> > > > [ 1756.728679]  #1:  (&inode->i_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> > > > [ 1756.728923]  [<c1003d57>] show_trace_log_lvl+0x1a/0x30
> > > > [ 1756.729015]  [<c1003d7f>] show_trace+0x12/0x14
> > > > [ 1756.729103]  [<c1003e79>] dump_stack+0x16/0x18
> > > > [ 1756.729187]  [<c102c2e8>] run_workqueue+0x167/0x170
> > > > [ 1756.729276]  [<c102c437>] worker_thread+0x146/0x165
> > > > [ 1756.729368]  [<c102f797>] kthread+0x97/0xc4
> > > > [ 1756.729456]  [<c1003bdb>] kernel_thread_helper+0x7/0x10
> > > > [ 1756.729547]  =======================
> > > > [ 1792.436492] svc: unknown version (0 for prog 100003, nfsd)
> > > > [ 1846.683648] BUG: workqueue leaked lock or atomic: nfsd4/0x00000000/3577
> > > > [ 1846.683701]     last function: laundromat_main+0x0/0x69 [nfsd]
> > > > [ 1846.683832] 2 locks held by nfsd4/3577:
> > > > [ 1846.683885]  #0:  (client_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> > > > [ 1846.683980]  #1:  (&inode->i_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> > > > [ 1846.683988]  [<c1003d57>] show_trace_log_lvl+0x1a/0x30
> > > > [ 1846.683994]  [<c1003d7f>] show_trace+0x12/0x14
> > > > [ 1846.683997]  [<c1003e79>] dump_stack+0x16/0x18
> > > > [ 1846.684001]  [<c102c2e8>] run_workqueue+0x167/0x170
> > > > [ 1846.684006]  [<c102c437>] worker_thread+0x146/0x165
> > > > [ 1846.684012]  [<c102f797>] kthread+0x97/0xc4
> > > > [ 1846.684023]  [<c1003bdb>] kernel_thread_helper+0x7/0x10
> > > 
> > > Oleg, that's a fairly incomprehensible message we have in there.  Can you
> > > please explain what it means?
> > 
> > I think I'm responsible for this message (commit
> > d5abe669172f20a4129a711de0f250a4e07db298); what is says is that the
> > function executed by the workqueue (here laundromat_main) leaked an
> > atomic context or is still holding locks (2 locks in this case).
> > 
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