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Re: [PATCH] Move vn_iowait() earlier in the reclaim path

To: Lachlan McIlroy <lachlan@xxxxxxx>, xfs@xxxxxxxxxxx, xfs-dev <xfs-dev@xxxxxxx>
Subject: Re: [PATCH] Move vn_iowait() earlier in the reclaim path
From: Lachlan McIlroy <lachlan@xxxxxxx>
Date: Tue, 05 Aug 2008 17:52:34 +1000
In-reply-to: <20080805073711.GA21635@disturbed>
References: <4897F691.6010806@xxxxxxx> <20080805073711.GA21635@disturbed>
Reply-to: lachlan@xxxxxxx
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Thunderbird 2.0.0.16 (X11/20080707)
Dave Chinner wrote:
On Tue, Aug 05, 2008 at 04:43:29PM +1000, Lachlan McIlroy wrote:
Currently by the time we get to vn_iowait() in xfs_reclaim() we have already
gone through xfs_inactive()/xfs_free() and recycled the inode.  Any I/O

xfs_free()? What's that?
Sorry that should have been xfs_ifree() (we set the inode's mode to
zero in there).


completions still running (file size updates and unwritten extent conversions)
may be working on an inode that is no longer valid.

The linux inode does not get freed until after ->clear_inode
completes, hence it is perfectly valid to reference it anywhere
in the ->clear_inode path.
The problem I see is an assert in xfs_setfilesize() fail:

        ASSERT((ip->i_d.di_mode & S_IFMT) == S_IFREG);

The mode of the XFS inode is zero at this time.


My bet is that you are seeing I/O completion mark an inode dirty
that is being freed. ie.  Calling mark_inode_dirty_sync() in the I/O
completion blindly assumes that the linux inode is still valid, when it may be in the 'being freed' path. e.g. we can put it back on the
superblock dirty list just before it gets freed for real...

I came across this about a week ago when tracking down a QA failure
with a combined linux/XFS inode patch. The fix is to make I/O
completion call xfs_mark_inode_dirty_sync() so we check that this
linux inode not in the process of being freed before we try to
mark it dirty.

Cheers,

Dave.


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