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Re: [PATCH 19/19] XFS: set PF_FSTRANS while ilock is held in xfs_free_eo

To: NeilBrown <neilb@xxxxxxx>
Subject: Re: [PATCH 19/19] XFS: set PF_FSTRANS while ilock is held in xfs_free_eofblocks
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 16 Apr 2014 16:18:20 +1000
Cc: linux-mm@xxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140416040337.10604.7488.stgit@xxxxxxxxxxxxxx>
References: <20140416033623.10604.69237.stgit@xxxxxxxxxxxxxx> <20140416040337.10604.7488.stgit@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Apr 16, 2014 at 02:03:37PM +1000, NeilBrown wrote:
> memory allocates can happen while the xfs ilock is held in
> xfs_free_eofblocks, particularly
> 
>   [<ffffffff813e6667>] kmem_zone_alloc+0x67/0xc0
>   [<ffffffff813e5945>] xfs_trans_add_item+0x25/0x50
>   [<ffffffff8143d64c>] xfs_trans_ijoin+0x2c/0x60
>   [<ffffffff8142275e>] xfs_itruncate_extents+0xbe/0x400
>   [<ffffffff813c72f4>] xfs_free_eofblocks+0x1c4/0x240
> 
> So set PF_FSTRANS to avoid this causing a deadlock.

Another "You broke KM_NOFS" moment. You win a Kit Kat. ;)

xfs_trans_add_item():

        lidp = kmem_zone_zalloc(xfs_log_item_desc_zone, KM_SLEEP | KM_NOFS);

KM_NOFS needs to work, otherwise XFS is just a huge steaming pile of
memory reclaim deadlocks regardless of whether you are using
loopback NFS or not.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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