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From: Martin Kepplinger <martin.kepplinger@puri.sm>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Bart Van Assche <bvanassche@acm.org>,
	Can Guo <cang@codeaurora.org>,
	linux-scsi@vger.kernel.org, linux-block@vger.kernel.org,
	kernel@puri.sm
Subject: Re: [PATCH] block: Fix bug in runtime-resume handling
Date: Thu, 27 Aug 2020 19:42:43 +0200
Message-ID: <4c636f2d-af7f-bbde-a864-dbeb67c590ec@puri.sm> (raw)
In-Reply-To: <5152a510-bebf-bf33-f6b3-4549e50386ab@puri.sm>

On 26.08.20 09:48, Martin Kepplinger wrote:
> On 24.08.20 22:13, Alan Stern wrote:
>> On Mon, Aug 24, 2020 at 10:48:32AM -0700, Bart Van Assche wrote:
>>> On 2020-08-23 07:57, Alan Stern wrote:
>>>> The problem is fixed by checking that the queue's runtime-PM status
>>>> isn't RPM_SUSPENDED before allowing a request to be issued, [ ... ]
>>>
>>> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
>>>
>>> Can, can you help with testing this patch?
>>>
>>> Thanks,
>>>
>>> Bart.
>>
>> Martin:
>>
>> (I forgot to ask this question several weeks ago, while you were running 
>> your tests.  Better ask it now before I forget again...)
>>
>> I suspect the old runtime-PM code in the block layer would have worked 
>> okay in your SD cardreader test if the BLK_MQ_REQ_PREEMPT flag had not 
>> been set.  Do you know why the flag was set, or what line of code caused 
>> it to be set?
> 
> Correct. if not set, I could handle all I need in the scsi error path.

this thread becomes a bit confusing. I thought about REQ_FAILFAST_DEV
but you're talking about something different.

the only place I see BLK_MQ_REQ_PREEMPT getting passed on is in
__scsi_execute() which is the case when mounting/unmounting. At least
that about the only place I can find.

I remember *only* your block pm fix would let me mount/unmount, but not
use files yet (REQ_FAILFAST_DEV and so on).

When I revert your fix and remove BLK_MQ_REQ_PREEMPT from being passed
on to blk_get_request() in __scsi_execute(), that line gets executed
exactly once during startup and I'm missing the /dev/sda device from the
cardreader then.

Is this what you're asking?


> 
>>
>> As I recall, the request that failed was a read-ahead.  It's not clear 
>> to me why such a request would need to have BLK_MQ_REQ_PREEMPT set.  
>> Although there may be other reasons for having that flag, at this point 
>> we're concerned with requests that are part of the runtime-resume 
>> procedure.  A read-ahead does not fall into that category.
>>
>> Do you think you can find the answer?  Perhaps we should add a separate 
>> BLK_MQ_REQ_PM flag.



  reply index

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 11:10 [PATCH] scsi: sd: add runtime pm to open / release Martin Kepplinger
2020-06-24 13:33 ` Bart Van Assche
2020-06-25  8:16   ` Martin Kepplinger
2020-06-25 14:52     ` Alan Stern
2020-06-26  3:53     ` Bart Van Assche
2020-06-26 15:07     ` Bart Van Assche
2020-06-26 15:44       ` Alan Stern
2020-06-28  2:37         ` Bart Van Assche
2020-06-28 13:10           ` Alan Stern
2020-06-29  9:42         ` Martin Kepplinger
2020-06-29 16:15           ` Alan Stern
2020-06-29 16:56             ` Bart Van Assche
2020-06-29 17:40               ` Alan Stern
2020-06-30  3:33             ` Martin Kepplinger
2020-06-30 13:38               ` Alan Stern
2020-06-30 15:59             ` Bart Van Assche
2020-06-30 18:02               ` Alan Stern
2020-06-30 19:23                 ` Bart Van Assche
2020-06-30 19:38                   ` Alan Stern
2020-06-30 23:31                     ` Bart Van Assche
2020-07-01  0:49                       ` Alan Stern
2020-07-06 16:41                         ` Alan Stern
2020-07-28  7:02                           ` Martin Kepplinger
2020-07-28 20:02                             ` Alan Stern
2020-07-29 14:12                               ` Martin Kepplinger
2020-07-29 14:32                                 ` Alan Stern
2020-07-29 14:44                                   ` Martin K. Petersen
2020-07-29 14:56                                     ` Alan Stern
2020-07-29 14:46                                   ` James Bottomley
2020-07-29 14:53                                     ` James Bottomley
2020-07-29 15:40                                       ` Martin Kepplinger
2020-07-29 15:44                                         ` James Bottomley
2020-07-29 16:43                                           ` Martin Kepplinger
2020-07-29 18:25                                             ` Alan Stern
2020-07-29 18:29                                               ` James Bottomley
2020-07-30  8:52                                                 ` Martin Kepplinger
2020-07-30  8:54                                                   ` Martin Kepplinger
2020-07-30 15:10                                                   ` Alan Stern
2020-08-04  9:39                                                     ` Martin Kepplinger
2020-08-07  9:51                                                       ` Martin Kepplinger
2020-08-07 14:30                                                         ` Alan Stern
2020-08-08  6:59                                                           ` Martin Kepplinger
2020-08-08 15:05                                                             ` Alan Stern
2020-08-09  9:20                                                               ` Martin Kepplinger
2020-08-09 15:26                                                                 ` Alan Stern
2020-08-10 12:03                                                                   ` Martin Kepplinger
2020-08-10 14:13                                                                     ` Alan Stern
2020-08-11  7:55                                                                       ` Martin Kepplinger
2020-08-11 13:48                                                                         ` Alan Stern
2020-08-23 14:57                                                                         ` [PATCH] block: Fix bug in runtime-resume handling Alan Stern
2020-08-24 17:48                                                                           ` Bart Van Assche
2020-08-24 20:13                                                                             ` Alan Stern
2020-08-26  7:48                                                                               ` Martin Kepplinger
2020-08-27 17:42                                                                                 ` Martin Kepplinger [this message]
2020-08-27 20:29                                                                                   ` Alan Stern
2020-08-29  7:24                                                                                     ` Martin Kepplinger
2020-08-29 15:26                                                                                       ` Alan Stern
2020-08-29 16:33                                                                                         ` Martin Kepplinger
2020-08-29 18:56                                                                                           ` Alan Stern
2020-08-30  0:38                                                                                             ` Bart Van Assche
2020-08-30  1:06                                                                                               ` Alan Stern
2020-07-29 15:40                                       ` [PATCH] scsi: sd: add runtime pm to open / release Alan Stern
2020-07-29 15:49                                         ` James Bottomley
2020-07-29 16:17                                           ` Alan Stern
2020-07-29 15:52                                         ` Martin Kepplinger
2020-07-29 18:10                                   ` Douglas Gilbert
2020-07-30  8:05             ` Martin Kepplinger
2020-07-30 15:14               ` Alan Stern

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