[1/2] blk-flush: fix rq->flush.seq for post-flush requests

  From: Chengming Zhou <zhouchengming@bytedance.com>

If the policy == (REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH), it means that the
data sequence and post-flush sequence need to be done for this request.

The rq->flush.seq should record what sequences have been done (or don't
need to be done). So in this case, pre-flush doesn't need to be done,
we should init rq->flush.seq to REQ_FSEQ_PREFLUSH not REQ_FSEQ_POSTFLUSH.

Of course, this doesn't cause any problem in fact, since pre-flush and
post-flush sequence do the same thing for now.

But we'd better fix this value, and the next patch will depend on this
value to be correct.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-flush.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On Mon, Jul 10, 2023 at 02:47:04PM +0800, chengming.zhou@linux.dev wrote:
> From: Chengming Zhou <zhouchengming@bytedance.com>
> 
> If the policy == (REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH), it means that the
> data sequence and post-flush sequence need to be done for this request.
> 
> The rq->flush.seq should record what sequences have been done (or don't
> need to be done). So in this case, pre-flush doesn't need to be done,
> we should init rq->flush.seq to REQ_FSEQ_PREFLUSH not REQ_FSEQ_POSTFLUSH.
> 
> Of course, this doesn't cause any problem in fact, since pre-flush and
> post-flush sequence do the same thing for now.

I wonder if it really doesn't cause any problems, but the change for
sure looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

It should probably go before your other flush optimizations and maybe
grow a fixes tag.
  

On 2023/7/10 21:30, Christoph Hellwig wrote:
> On Mon, Jul 10, 2023 at 02:47:04PM +0800, chengming.zhou@linux.dev wrote:
>> From: Chengming Zhou <zhouchengming@bytedance.com>
>>
>> If the policy == (REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH), it means that the
>> data sequence and post-flush sequence need to be done for this request.
>>
>> The rq->flush.seq should record what sequences have been done (or don't
>> need to be done). So in this case, pre-flush doesn't need to be done,
>> we should init rq->flush.seq to REQ_FSEQ_PREFLUSH not REQ_FSEQ_POSTFLUSH.
>>
>> Of course, this doesn't cause any problem in fact, since pre-flush and
>> post-flush sequence do the same thing for now.
> 
> I wonder if it really doesn't cause any problems, but the change for
> sure looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 
> It should probably go before your other flush optimizations and maybe
> grow a fixes tag.

Ok, will add a Fixes tag and send it as a separate patch since it's a bug fix.

Thanks.
  

On 2023/7/11 19:06, Chengming Zhou wrote:
> On 2023/7/10 21:30, Christoph Hellwig wrote:
>> On Mon, Jul 10, 2023 at 02:47:04PM +0800, chengming.zhou@linux.dev wrote:
>>> From: Chengming Zhou <zhouchengming@bytedance.com>
>>>
>>> If the policy == (REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH), it means that the
>>> data sequence and post-flush sequence need to be done for this request.
>>>
>>> The rq->flush.seq should record what sequences have been done (or don't
>>> need to be done). So in this case, pre-flush doesn't need to be done,
>>> we should init rq->flush.seq to REQ_FSEQ_PREFLUSH not REQ_FSEQ_POSTFLUSH.
>>>
>>> Of course, this doesn't cause any problem in fact, since pre-flush and
>>> post-flush sequence do the same thing for now.
>>
>> I wonder if it really doesn't cause any problems, but the change for
>> sure looks good:
>>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>
>> It should probably go before your other flush optimizations and maybe
>> grow a fixes tag.
> 
> Ok, will add a Fixes tag and send it as a separate patch since it's a bug fix.
> 

Well, I should put it in that series before other flush optimizations instead.
  

On Tue, Jul 11, 2023 at 07:06:20PM +0800, Chengming Zhou wrote:
> Ok, will add a Fixes tag and send it as a separate patch since it's a bug fix.

Btw, it's probably not worth resending patch 2 until we've figured out
and dealt with the SATA flush regression that Chuck reported.
  

On 2023/7/11 19:31, Christoph Hellwig wrote:
> On Tue, Jul 11, 2023 at 07:06:20PM +0800, Chengming Zhou wrote:
>> Ok, will add a Fixes tag and send it as a separate patch since it's a bug fix.
> 
> Btw, it's probably not worth resending patch 2 until we've figured out
> and dealt with the SATA flush regression that Chuck reported.

Ok, I will not resend patch 2. As for the patch 1, should I resend it as a separate patch
or just put it in that series [1] before other flush optimizations ?

I search on the block mail list, find the issue [2] you mentioned, will look into it too.

[1] https://lore.kernel.org/lkml/20230707093722.1338589-1-chengming.zhou@linux.dev/
[2] https://lore.kernel.org/linux-block/7A57C7AE-A51A-4254-888B-FE15CA21F9E9@oracle.com/
  

On Tue, Jul 11, 2023 at 07:52:11PM +0800, Chengming Zhou wrote:
> On 2023/7/11 19:31, Christoph Hellwig wrote:
> > On Tue, Jul 11, 2023 at 07:06:20PM +0800, Chengming Zhou wrote:
> >> Ok, will add a Fixes tag and send it as a separate patch since it's a bug fix.
> > 
> > Btw, it's probably not worth resending patch 2 until we've figured out
> > and dealt with the SATA flush regression that Chuck reported.
> 
> Ok, I will not resend patch 2. As for the patch 1, should I resend it as a separate patch
> or just put it in that series [1] before other flush optimizations ?

I'd wait a bit for debugging the regression.  For the worst case we'll have
to revert the patch, which currently can be done cleanly, but can't be
with that patch.