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Re: Hang in XFS reclaim on 3.7.0-rc3

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Hang in XFS reclaim on 3.7.0-rc3
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 1 Nov 2012 16:30:10 -0500
Cc: Torsten Kaiser <just.for.lkml@xxxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20121029222613.GU29378@dastard>
References: <CAPVoSvSM9=hictqwT2rzZA-fU_XSwd-_FRzW_J+HQYj7iohTWQ@xxxxxxxxxxxxxx> <20121029222613.GU29378@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
Hi Dave,

On Tue, Oct 30, 2012 at 09:26:13AM +1100, Dave Chinner wrote:
> On Mon, Oct 29, 2012 at 09:03:15PM +0100, Torsten Kaiser wrote:
> > After experiencing a hang of all IO yesterday (
> > http://marc.info/?l=linux-kernel&m=135142236520624&w=2 ), I turned on
> > LOCKDEP after upgrading to -rc3.
> > 
> > I then tried to replicate the load that hung yesterday and got the
> > following lockdep report, implicating XFS instead of by stacking swap
> > onto dm-crypt and md.
> > 
> > [ 2844.971913]
> > [ 2844.971920] =================================
> > [ 2844.971921] [ INFO: inconsistent lock state ]
> > [ 2844.971924] 3.7.0-rc3 #1 Not tainted
> > [ 2844.971925] ---------------------------------
> > [ 2844.971927] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
> > [ 2844.971929] kswapd0/725 [HC0[0]:SC0[0]:HE1:SE1] takes:
> > [ 2844.971931] (&(&ip->i_lock)->mr_lock){++++?.}, at: [<ffffffff811e7ef4>] 
> > xfs_ilock+0x84/0xb0
> > [ 2844.971941] {RECLAIM_FS-ON-W} state was registered at:
> > [ 2844.971942]   [<ffffffff8108137e>] mark_held_locks+0x7e/0x130
> > [ 2844.971947]   [<ffffffff81081a63>] lockdep_trace_alloc+0x63/0xc0
> > [ 2844.971949]   [<ffffffff810e9dd5>] kmem_cache_alloc+0x35/0xe0
> > [ 2844.971952]   [<ffffffff810dba31>] vm_map_ram+0x271/0x770
> > [ 2844.971955]   [<ffffffff811e10a6>] _xfs_buf_map_pages+0x46/0xe0
> > [ 2844.971959]   [<ffffffff811e1fba>] xfs_buf_get_map+0x8a/0x130
> > [ 2844.971961]   [<ffffffff81233849>] xfs_trans_get_buf_map+0xa9/0xd0
> > [ 2844.971964]   [<ffffffff8121e339>] xfs_ifree_cluster+0x129/0x670
> > [ 2844.971967]   [<ffffffff8121f959>] xfs_ifree+0xe9/0xf0
> > [ 2844.971969]   [<ffffffff811f4abf>] xfs_inactive+0x2af/0x480
> > [ 2844.971972]   [<ffffffff811efb90>] xfs_fs_evict_inode+0x70/0x80
> > [ 2844.971974]   [<ffffffff8110cb8f>] evict+0xaf/0x1b0
> > [ 2844.971977]   [<ffffffff8110cd95>] iput+0x105/0x210
> > [ 2844.971979]   [<ffffffff811070d0>] dentry_iput+0xa0/0xe0
> > [ 2844.971981]   [<ffffffff81108310>] dput+0x150/0x280
> > [ 2844.971983]   [<ffffffff811020fb>] sys_renameat+0x21b/0x290
> > [ 2844.971986]   [<ffffffff81102186>] sys_rename+0x16/0x20
> > [ 2844.971988]   [<ffffffff816b2292>] system_call_fastpath+0x16/0x1b
> 
> We shouldn't be mapping pages there. See if the patch below fixes
> it.
> 
> Fundamentally, though, the lockdep warning has come about because
> vm_map_ram is doing a GFP_KERNEL allocation when we need it to be
> doing GFP_NOFS - we are within a transaction here, so memory reclaim
> is not allowed to recurse back into the filesystem.
> 
> mm-folk: can we please get this vmalloc/gfp_flags passing API
> fixed once and for all? This is the fourth time in the last month or
> so that I've seen XFS bug reports with silent hangs and associated
> lockdep output that implicate GFP_KERNEL allocations from vm_map_ram
> in GFP_NOFS conditions as the potential cause....
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@xxxxxxxxxxxxx
> 
> xfs: don't vmap inode cluster buffers during free

Could you write up a little more background for the commit message?

Regards,
        Ben

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