Re: [PATCH] btrfs: fix false EIO for missing device

[Liu Bo <bo.li.liu@oracle.com>]

On Fri, Oct 13, 2017 at 09:42:18PM +0800, Anand Jain wrote:
> When one of the device is missing, bbio_error() takes care
> of setting the error status. And if its only IO that is
> pending in that stripe, it fails to check the status of the
> other IO at %bbio_error before setting the error %bi_status
> for the %orig_bio. Fix this by checking if %bbio->error is
> has crossed the %bbio->max_errors. Thxs.
> 
> Reproducer as below fdatasync error is seen intermittently.
> 
>  mount -o degraded /dev/sdc /btrfs
>  dd status=none if=/dev/zero of=$(mktemp /btrfs/XXX) bs=4096 count=1 conv=fdatasync
> 
>  dd: fdatasync failed for ‘/btrfs/LSe’: Input/output error
> 
>  The reason for the intermittences of the problem is because..
>  following condition has to be met, which depends on timely
>  coordination.
>  In btrfs_map_bio()
>   . The RAID1 the missing device has to be at %dev_nr = 1
>  In bbio_error()
>   . Before bbio_error() is called the bio of the not-missing
>     device at %dev_nr=0 must be completed so that the below
>     condition is true
>      if (atomic_dec_and_test(&bbio->stripes_pending)) {
>


> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/volumes.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9af633dcf015..efd502176915 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6131,7 +6131,10 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
>  
>  		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
>  		bio->bi_iter.bi_sector = logical >> 9;
> -		bio->bi_status = BLK_STS_IOERR;
> +		if (atomic_read(&bbio->error) > bbio->max_errors)
> +			bio->bi_status = BLK_STS_IOERR;
> +		else
> +			bio->bi_status = 0;

Thanks for the fix, I'd prefer BLK_STS_OK rather than 0.

With that,

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

-liubo
>  		btrfs_end_bbio(bbio, bio);
>  	}
>  }
> -- 
> 2.13.1
> 
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