[PATCH] loop: clear wb_err in bd_inode when detaching backing file

[PATCH] loop: clear wb_err in bd_inode when detaching backing file

[Jeff Layton]

From: Jeff Layton <jlayton@redhat.com>

When a loop block device encounters a writeback error, that error will
get propagated to the bd_inode's wb_err field. If we then detach the
backing file from it, attach another and fsync it, we'll get back the
writeback error that we had from the previous backing file.

This is a bit of a grey area as POSIX doesn't cover loop devices, but it
is somewhat counterintuitive.

If we detach a backing file from the loopdev while there are still
unreported errors, take it as a sign that we're no longer interested in
the previous file, and clear out the wb_err in the loop blockdev.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 drivers/block/loop.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5d4e31655d96..55cf554bc914 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1068,6 +1068,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	if (bdev) {
 		bdput(bdev);
 		invalidate_bdev(bdev);
+		bdev->bd_inode->i_mapping->wb_err = 0;
 	}
 	set_capacity(lo->lo_disk, 0);
 	loop_sysfs_exit(lo);
-- 
2.17.0

Re: [PATCH] loop: clear wb_err in bd_inode when detaching backing file

[Jeff Layton]

On Mon, 2018-05-21 at 08:37 -0400, Jeff Layton wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> When a loop block device encounters a writeback error, that error will
> get propagated to the bd_inode's wb_err field. If we then detach the
> backing file from it, attach another and fsync it, we'll get back the
> writeback error that we had from the previous backing file.
> 
> This is a bit of a grey area as POSIX doesn't cover loop devices, but it
> is somewhat counterintuitive.
> 
> If we detach a backing file from the loopdev while there are still
> unreported errors, take it as a sign that we're no longer interested in
> the previous file, and clear out the wb_err in the loop blockdev.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  drivers/block/loop.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 5d4e31655d96..55cf554bc914 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1068,6 +1068,7 @@ static int loop_clr_fd(struct loop_device *lo)
>  	if (bdev) {
>  		bdput(bdev);
>  		invalidate_bdev(bdev);
> +		bdev->bd_inode->i_mapping->wb_err = 0;
>  	}
>  	set_capacity(lo->lo_disk, 0);
>  	loop_sysfs_exit(lo);

Jens,

I sent this to the mailing lists earlier, but it occurs to me that
loop.c changes should probably go through the block tree. Would you
mind picking this up and feeding it to next and on to Linus?

I think we probably want this in v4.17 if possible, as it is a
regression from v4.16 (due to commit b4678df184b3) and was causing some
failures in xfstests runs.

Hmm, now that I think about it, we should probably also give Ted
"Reported-and-Tested-by" credit here too. Let me know if you'd rather I
resend with that added.

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>

Re: [PATCH] loop: clear wb_err in bd_inode when detaching backing file

[Jens Axboe]

On 5/21/18 12:26 PM, Jeff Layton wrote:
> On Mon, 2018-05-21 at 08:37 -0400, Jeff Layton wrote:
>> From: Jeff Layton <jlayton@redhat.com>
>>
>> When a loop block device encounters a writeback error, that error will
>> get propagated to the bd_inode's wb_err field. If we then detach the
>> backing file from it, attach another and fsync it, we'll get back the
>> writeback error that we had from the previous backing file.
>>
>> This is a bit of a grey area as POSIX doesn't cover loop devices, but it
>> is somewhat counterintuitive.
>>
>> If we detach a backing file from the loopdev while there are still
>> unreported errors, take it as a sign that we're no longer interested in
>> the previous file, and clear out the wb_err in the loop blockdev.
>>
>> Signed-off-by: Jeff Layton <jlayton@redhat.com>
>> ---
>>  drivers/block/loop.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
>> index 5d4e31655d96..55cf554bc914 100644
>> --- a/drivers/block/loop.c
>> +++ b/drivers/block/loop.c
>> @@ -1068,6 +1068,7 @@ static int loop_clr_fd(struct loop_device *lo)
>>  	if (bdev) {
>>  		bdput(bdev);
>>  		invalidate_bdev(bdev);
>> +		bdev->bd_inode->i_mapping->wb_err = 0;
>>  	}
>>  	set_capacity(lo->lo_disk, 0);
>>  	loop_sysfs_exit(lo);
> 
> Jens,
> 
> I sent this to the mailing lists earlier, but it occurs to me that
> loop.c changes should probably go through the block tree. Would you
> mind picking this up and feeding it to next and on to Linus?
> 
> I think we probably want this in v4.17 if possible, as it is a
> regression from v4.16 (due to commit b4678df184b3) and was causing some
> failures in xfstests runs.
> 
> Hmm, now that I think about it, we should probably also give Ted
> "Reported-and-Tested-by" credit here too. Let me know if you'd rather I
> resend with that added.

Yeah, I can funnel it for 4.17 - a quick resend with the right
attributions would be appreciated, thanks.

-- 
Jens Axboe