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Re: [PATCH 1/5] xfs: don't try to mark uncached buffers stale on error.

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/5] xfs: don't try to mark uncached buffers stale on error.
From: Ben Myers <bpm@xxxxxxx>
Date: Tue, 24 Sep 2013 10:33:24 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1380002476-18839-2-git-send-email-david@xxxxxxxxxxxxx>
References: <1380002476-18839-1-git-send-email-david@xxxxxxxxxxxxx> <1380002476-18839-2-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Hi Dave,

On Tue, Sep 24, 2013 at 04:01:12PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> fsstress failed during a shutdown with the following assert:
> 
> XFS: Assertion failed: xfs_buf_islocked(bp), file: fs/xfs/xfs_buf.c, line: 143
> .....
>  xfs_buf_stale+0x3f/0xf0
>  xfs_bioerror_relse+0x2d/0x90
>  xfsbdstrat+0x51/0xa0

Here you're showing an assert reported through an xfsbdstrat codepath...

>  xfs_zero_remaining_bytes+0x1d1/0x2d0
>  xfs_free_file_space+0x5d0/0x600
>  xfs_change_file_space+0x251/0x3a0
>  xfs_ioc_space+0xcc/0x130
> .....
> 
> xfs_zero_remaining_bytes() works with uncached buffers, and hence if
> we are preventing IO due to a shutdown, we should not be marking it
> stale as that is only for cached buffers. Instead, just mark it with
> an error and make sure it gets to the caller.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_buf.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 2634700..956685f 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1093,25 +1093,20 @@ xfs_bioerror_relse(
>       struct xfs_buf  *bp)
>  {
>       int64_t         fl = bp->b_flags;
> +
>       /*
> -      * No need to wait until the buffer is unpinned.
> -      * We aren't flushing it.
> -      *
> -      * chunkhold expects B_DONE to be set, whether
> -      * we actually finish the I/O or not. We don't want to
> -      * change that interface.
> +      * No need to wait until the buffer is unpinned. We aren't flushing it.
>        */
>       XFS_BUF_UNREAD(bp);
>       XFS_BUF_DONE(bp);
>       xfs_buf_stale(bp);
>       bp->b_iodone = NULL;
> +
> +     /*
> +      * There's no reason to mark error for ASYNC buffers as there is no-one
> +      * waiting to collect the error.
> +      */
>       if (!(fl & XBF_ASYNC)) {
> -             /*
> -              * Mark b_error and B_ERROR _both_.
> -              * Lot's of chunkcache code assumes that.
> -              * There's no reason to mark error for
> -              * ASYNC buffers.
> -              */
>               xfs_buf_ioerror(bp, EIO);
>               complete(&bp->b_iowait);
>       } else {
> @@ -1128,11 +1123,15 @@ xfs_bdstrat_cb(
>       if (XFS_FORCED_SHUTDOWN(bp->b_target->bt_mount)) {
>               trace_xfs_bdstrat_shut(bp, _RET_IP_);
>               /*
> -              * Metadata write that didn't get logged but
> -              * written delayed anyway. These aren't associated
> -              * with a transaction, and can be ignored.
> +              * If this is a cached write, then it is likely to be a delayed
> +              * write metadata buffer that can be ignored because the
> +              * contents are logged. If it's an uncached buffer or a read
> +              * operation, then the caller will get the error through the
> +              * normal IO completion path. We can tell if the buffer is
> +              * cached or not by looking to see if the b_pag field is NULL or
> +              * not.
>                */
> -             if (!bp->b_iodone && !XFS_BUF_ISREAD(bp))
> +             if (!bp->b_iodone && !XFS_BUF_ISREAD(bp) && bp->b_pag)

...but it looks like your fix is in xfs_bdstrat_cb, which wouldn't have been
involved in the stack you posted above.  What am I missing?

Thanks,
        Ben

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