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Re: [PATCH RFC] fs: xfs: Fix xfs_trans_read_buf event tracing

To: Pratyush Anand <panand@xxxxxxxxxx>, david@xxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: [PATCH RFC] fs: xfs: Fix xfs_trans_read_buf event tracing
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 19 Feb 2015 10:39:22 -0600
Cc: jbastian@xxxxxxxxxx, ddutile@xxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <7fb3278485ca5d8b48cd1ba980be6cc11dafc11b.1424352124.git.panand@xxxxxxxxxx>
References: <7fb3278485ca5d8b48cd1ba980be6cc11dafc11b.1424352124.git.panand@xxxxxxxxxx>
On 2/19/15 7:24 AM, Pratyush Anand wrote:
> My root file system is xfs. As soon as I enable event for
> xfs_trans_read_buf `echo xfs:xfs_trans_read_buf >>
> /sys/kernel/debug/tracing/set_event`, I see a kernel panic.
> 
> A little bit of debugging shows that bp->b_fspriv is NULL many a time
> when trace_xfs_trans_read_buf(bp->b_fspriv) is called.
> 
> I do not have any idea about xfs filesystem. So, I am not sure, if it
> is expected to have bp->b_fspriv = NULL at this location.
> 
> This patch fixes the issue, until we have a better fix.

What kernel did you hit this on?  What did the backtrace look like?

I've been unable to reproduce the problem so far.

Thanks,
-Eric

> Signed-off-by: Pratyush Anand <panand@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_trans_buf.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
> index 0a4d4ab6d9a9..0b67a20643bf 100644
> --- a/fs/xfs/xfs_trans_buf.c
> +++ b/fs/xfs/xfs_trans_buf.c
> @@ -329,7 +329,8 @@ xfs_trans_read_buf_map(
>  
>       if (tp)
>               _xfs_trans_bjoin(tp, bp, 1);
> -     trace_xfs_trans_read_buf(bp->b_fspriv);
> +     if (bp->b_fspriv)
> +             trace_xfs_trans_read_buf(bp->b_fspriv);
>       *bpp = bp;
>       return 0;
>  
> 

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