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Re: [PATCH 6/6] XFS: Prevent looping in xfs_sync_inodes_ag

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 6/6] XFS: Prevent looping in xfs_sync_inodes_ag
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 9 Oct 2008 11:02:01 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20081008182138.GB22941@xxxxxxxxxxxxx>
Mail-followup-to: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <1223416480-7701-1-git-send-email-david@xxxxxxxxxxxxx> <1223416480-7701-7-git-send-email-david@xxxxxxxxxxxxx> <20081008182138.GB22941@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Wed, Oct 08, 2008 at 02:21:38PM -0400, Christoph Hellwig wrote:
> On Wed, Oct 08, 2008 at 08:54:40AM +1100, Dave Chinner wrote:
> > If the last  block of the AG has inodes in it and the AG is an
> > exactly power-of-2 size then the last inode in the AG points
> > to the last block in the AG. If we try to find the next inode
> > in the AG by adding one to the inode number, we increment the
> > inode number past the size of the AG. The result is that the
> > macro XFS_INO_TO_AGINO() will strip the AG portion of the inode
> > number and return an inode number of zero.
> > 
> > That is, instead of terminating the lookup loop because we hit the
> > inode number went outside the valid range for the AG, the search
> > index returns to zero and we start traversing the radix tree from
> > the start again. This results in an endless loop in
> > xfs_sync_inodes_ag().
> > 
> > Fix it be detecting if the new search index decreases as a result of
> > incrementing the current inode number. That indicate an overflow and
> > hence that we have finished processing the AG so we can terminate
> > the loop.
> Shouldn't this get merged into the patch that introduces the radix-tree
> based sync?

It could be, but I didn't want to have to redo that reviewed patch
series. I've only hit this problem once in the past 6 weeks so I
thought adding a new patch rather than modifying patches to add the
fix was a better way to go....

I can integrate it if you want....


Dave Chinner

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