[PATCH] XFS: Don't flush stale inodes

[Alex Elder]

Dave Chinner wrote:
> Because inodes remain in cache much longer than inode buffers do
> under memory pressure, we can get the situation where we have stale,
> dirty inodes being reclaimed but the backing storage has been freed.
> Hence we should never, ever flush XFS_ISTALE inodes to disk as
> there is no guarantee that the backing buffer is in cache and
> still marked stale when the flush occurs.

Looks good.  Seems like this could be the source of
some pretty gnarly problems.

> Signed-off-by: Dave Chinner <david at fromorbit.com>

Reviewed-by: Alex Elder <aelder at sgi.com>

> ---
>  fs/xfs/xfs_inode.c |   10 +++++++---
>  1 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index c2618db..e5c9953 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2846,10 +2846,14 @@ xfs_iflush(
>  	mp = ip->i_mount;
> 
>  	/*
> -	 * If the inode isn't dirty, then just release the inode
> -	 * flush lock and do nothing.
> +	 * If the inode isn't dirty, then just release the inode flush lock and
> +	 * do nothing. Treat stale inodes the same; we cannot rely on the
> +	 * backing buffer remaining stale in cache for the remaining life of
> +	 * the stale inode and so xfs_itobp() below may give us a buffer that
> +	 * no longer contains inodes below. Doing this stale check here also
> +	 * avoids forcing the log on pinned, stale inodes.
>  	 */
> -	if (xfs_inode_clean(ip)) {
> +	if (xfs_inode_clean(ip) || xfs_iflags_test(ip, XFS_ISTALE)) {
>  		xfs_ifunlock(ip);
>  		return 0;
>  	}