linux-kernel - Re: [PATCH 3.16 102/305] xfs: xfs_iflush

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Message-ID: <20160813233652.GU19025@dastard>
Date:	Sun, 14 Aug 2016 09:36:52 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	akpm@...ux-foundation.org, Christoph Hellwig <hch@....de>,
	Shyam Kaushik <shyam@...arastorage.com>,
	Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH 3.16 102/305] xfs: xfs_iflush_cluster fails to abort on
 error

On Sat, Aug 13, 2016 at 06:42:51PM +0100, Ben Hutchings wrote:
> 3.16.37-rc1 review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Dave Chinner <dchinner@...hat.com>
> 
> commit b1438f477934f5a4d5a44df26f3079a7575d5946 upstream.
> 
> When a failure due to an inode buffer occurs, the error handling
> fails to abort the inode writeback correctly. This can result in the
> inode being reclaimed whilst still in the AIL, leading to
> use-after-free situations as well as filesystems that cannot be
> unmounted as the inode log items left in the AIL never get removed.
> 
> Fix this by ensuring fatal errors from xfs_imap_to_bp() result in
> the inode flush being aborted correctly.
....
>  
>  	/*
> -	 * Get the buffer containing the on-disk inode.
> +	 * Get the buffer containing the on-disk inode. We are doing a try-lock
> +	 * operation here, so we may get  an EAGAIN error. In that case, we
> +	 * simply want to return with the inode still dirty.
> +	 *
> +	 * If we get any other error, we effectively have a corruption situation
> +	 * and we cannot flush the inode, so we treat it the same as failing
> +	 * xfs_iflush_int().
>  	 */
>  	error = xfs_imap_to_bp(mp, NULL, &ip->i_imap, &dip, &bp, XBF_TRYLOCK,
>  			       0);
> -	if (error || !bp) {
> +	if (error == -EAGAIN) {

Wrong. As was pointed out for other -stable trees after users
reported regressions, the error signs in XFS changed from positive
to negative in 3.17-rc1.

-Dave.
-- 
Dave Chinner
david@...morbit.com