linux-kernel - Re: drop_pagecache: Possible circular locking dependency

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Date:	Mon, 4 Dec 2006 17:37:18 +0800
From:	Fengguang Wu <fengguang.wu@...il.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: drop_pagecache: Possible circular locking dependency

On Mon, Dec 04, 2006 at 12:32:17AM -0800, Andrew Morton wrote:
> On Mon, 4 Dec 2006 16:09:02 +0800
> Fengguang Wu <fengguang.wu@...il.com> wrote:
> 
> > Got the following message when doing some benchmarks.
> > I guess we should not hold inode_lock on calling invalidate_inode_pages().
> > Any ideas?
> > 
> > Fengguang Wu
> > 
> > =======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.19-rc6-mm2 #3
> > -------------------------------------------------------
> > rabench.sh/7467 is trying to acquire lock:
> >  (&journal->j_list_lock){--..}, at: [<ffffffff8113bdbc>] journal_try_to_free_buffers+0xdc/0x1c0
> > 
> > but task is already holding lock:
> >  (inode_lock){--..}, at: [<ffffffff810fe857>] drop_pagecache+0x67/0x120
> > 
> > which lock already depends on the new lock.
> > 
> 
> drat, I was afraid someone would notice.
> 
> It's Hard To Fix.  Removing /proc/sys/vm/drop_pagecache would in fact be 
> my preferred fix.

Or fix drop_pagecache_sb():
        Repeat until all possible pages freed:
                grab and save some inodes to a buffer
                zip their pages outside of inode_lock

Takes much more code though.

I'd like to move this sysctl interface to the upcoming /proc/filecache. 
Being a module, it helps reduce the kernel size :)

Fengguang Wu
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