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From: Alan Stern <stern@rowland.harvard.edu>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Martin Kepplinger <martin.kepplinger@puri.sm>,
	jejb@linux.ibm.com, Can Guo <cang@codeaurora.org>,
	martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel@puri.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
Date: Tue, 30 Jun 2020 14:02:55 -0400
Message-ID: <20200630180255.GA459638@rowland.harvard.edu> (raw)
In-Reply-To: <5231c57d-3f4e-1853-d4d5-cf7f04a32246@acm.org>

On Tue, Jun 30, 2020 at 08:59:00AM -0700, Bart Van Assche wrote:
> On 2020-06-29 09:15, Alan Stern wrote:
> > Aha.  Looking at this more closely, it's apparent that the code in 
> > blk-core.c contains a logic bug: It assumes that if the BLK_MQ_REQ_PREEMPT 
> > flag is set then the request can be issued regardless of the queue's 
> > runtime status.  That is not correct when the queue is suspended.
> 
> Are you sure of this? In the past (legacy block layer) no requests were
> processed for queues in state RPM_SUSPENDED. However, that function and
> its successor blk_pm_allow_request() are gone. The following code was
> removed by commit 7cedffec8e75 ("block: Make blk_get_request() block for
> non-PM requests while suspended").
> 
> static struct request *blk_pm_peek_request(struct request_queue *q,
>                                            struct request *rq)
> {
>         if (q->dev && (q->rpm_status == RPM_SUSPENDED ||
>             (q->rpm_status != RPM_ACTIVE && !(rq->cmd_flags & REQ_PM))))
>                 return NULL;
>         else
>                 return rq;
> }

No, it wasn't.  Another routine, blk_pm_allow_request(), was removed by 
that commit, but almost no other code was deleted.  Maybe you're thinking 
of a different commit?

In any case, I don't understand the point you're trying to make.

Here's what I _do_ understand: While the queue is in the RPM_SUSPENDED 
state, it can't carry out any requests at all.  If a request is added to 
the queue, the queue must be resumed before the request can be issued to 
the lower-layer drivers -- no matter what flags are set in the request.

Right now there doesn't seem to be any mechanism for resuming the queue 
if an REQ_PREEMPT request is added while the queue is suspended.

Alan Stern

  reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 11:10 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 [this message]
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
2020-07-29 15:40                                       ` 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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