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Re: [PATCH] xfs: fix double free of trans in log recovery on I/O error

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix double free of trans in log recovery on I/O error
From: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
Date: Sun, 24 Aug 2014 12:20:20 +0300
Cc: xfs@xxxxxxxxxxx, Dave Chinner <david@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1408648692-15957-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1408648692-15957-1-git-send-email-bfoster@xxxxxxxxxx>
Hi Brian,

On Thu, Aug 21, 2014 at 10:18 PM, Brian Foster <bfoster@xxxxxxxxxx> wrote:
> XFS log recovery builds up an xlog_recover object as it passes through
> the log operations on the physical log. These structures are managed via
> a hash table and are allocated when a new transaction is encountered and
> freed once a commit operation for the transaction is encountered.
>
> This state machine for active transactions is implemented by a
> combination of xlog_do_recovery_pass(), which walks through the log
> buffers and xlog_recover_process_data() which processes log operations
> within each buffer. The latter function decides whether to allocate a
> new xlog_recover, add to it or commit and ultimately free it.  If an
> error occurs at any point during the lifecycle of a particular
> xlog_recover, xlog_recover_process_data() frees the object and returns
> an error.
>
> xlog_recover_commit_trans() handles the final processing of the
> transaction. It submits whatever I/O is required for the transaction and
> frees xlog_recover object along with the transaction items it tracks. If
> an error occurs at the final stages of the commit operation, such as I/O
> failure, both xlog_recover_commit_trans() and
> xlog_recover_process_data() attempt to free the trans object.
>
> Modify xlog_recover_commit_trans() to only free the trans object on
> successful completion of the trans, including any I/O errors that might
> occur when recovering the log.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> ---
>
> Hi all,
>
> I found that the recent buffer I/O rework fixes didn't address the crash
> reproduced by the dm-flakey/log recovery test case I posted recently. I
> tracked the crash down to this, which allows the test to pass. This
> addresses the crash I saw when running the reproducer manually with the
> metadump that Alex posted as well.
>
> FWIW, I also went back and tested the xfs_buf_iowait() experiment in
> both scenarios (Alex's metadump and xfstests test) and they all
> reproduce the same crash for me. I think that either I'm still not
> reproducing the original problem, something else might have contaminated
> the original xfs_buf_iowait() test to give a false positive, or
> something else entirely is going on.
>
> Alex,
>
> If you have a chance, I think it might be interesting to see whether you
> reproduce any problems with this patch. It looks like this is a
> regression introduced by:
>
>         2a84108f xfs: free the list of recovery items on error
>
> ... but I have no idea if that's in whatever kernel you're running.
I am running kernel 3.8.13 with some changes (published at
https://github.com/zadarastorage/zadara-xfs-pushback), but this
problem also happens on pristine 3.8.13 from
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git,
branch linux-stable-3.8.y.

I do not have commit 2a84108f in this kernel. It was introduced in 3.14.
I applied your patch to 3.8.13, but it doesn't fix the issue. Same
problem happens when testing scenario that I described in
http://oss.sgi.com/pipermail/xfs/2014-August/037637.html.

Thanks,
Alex.

>
> Brian
>
>  fs/xfs/xfs_log_recover.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 176c4b3..daca9a6 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -3528,10 +3528,15 @@ out:
>         if (!list_empty(&done_list))
>                 list_splice_init(&done_list, &trans->r_itemq);
>
> -       xlog_recover_free_trans(trans);
> -
>         error2 = xfs_buf_delwri_submit(&buffer_list);
> -       return error ? error : error2;
> +
> +       if (!error)
> +               error = error2;
> +       /* caller frees trans on error */
> +       if (!error)
> +               xlog_recover_free_trans(trans);
> +
> +       return error;
>  }
>
>  STATIC int
> --
> 1.8.3.1
>

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