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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>,
	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 05:33:25 +0200
Message-ID: <823057f0-95cf-bfcf-c39f-ca5d7abe2372@puri.sm> (raw)
In-Reply-To: <20200629161536.GA405175@rowland.harvard.edu>

On 29.06.20 18:15, Alan Stern wrote:
> On Mon, Jun 29, 2020 at 11:42:59AM +0200, Martin Kepplinger wrote:
>>
>>
>> On 26.06.20 17:44, Alan Stern wrote:
>>> Martin's best approach would be to add some debugging code to find out why 
>>> blk_queue_enter() isn't calling bkl_pm_request_resume(), or why that call 
>>> doesn't lead to pm_request_resume().
>>>
>>> Alan Stern
>>>
>>
>> Hi Alan,
>>
>> blk_queue_enter() always - especially when sd is runtime suspended and I
>> try to mount as above - sets success to be true for me, so never
>> continues down to bkl_pm_request_resume(). All I see is "PM: Removing
>> info for No Bus:sda1".
> 
> 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.
> 
> Below is my attempt to fix this up.  I'm not sure that the patch is 
> entirely correct, but it should fix this logic bug.  I would appreciate a 
> critical review.
> 
> Martin, does this fix the problem?
> 

not quite: mounting works and resuming itself indeed happens now when
copying a file, but the I/O itself doesn't, but says "device offline or
changed":

[  167.167615] sd 0:0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result:
hostbyte=0x00 driverbyte=0x08 cmd_age=0s
[  167.167630] sd 0:0:0:0: [sda] tag#0 Sense Key : 0x6 [current]
[  167.167638] sd 0:0:0:0: [sda] tag#0 ASC=0x28 ASCQ=0x0
[  167.167648] sd 0:0:0:0: [sda] tag#0 CDB: opcode=0x28 28 00 00 00 24
c2 00 00 01 00
[  167.167658] blk_update_request: I/O error, dev sda, sector 9410 op
0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[  167.178327] FAT-fs (sda1): FAT read failed (blocknr 1218)
[  167.183895] sd 0:0:0:0: [sda] tag#0 device offline or changed
[  167.189695] blk_update_request: I/O error, dev sda, sector 5101888 op
0x0:(READ) flags 0x80700 phys_seg 8 prio class 0
[  167.200510] sd 0:0:0:0: [sda] tag#0 device offline or changed


and a later try to copy a file only yields (mostly my own debug prints):


[  371.110798] blk_queue_enter: wait_event: pm=0
[  371.300666] scsi_runtime_resume
[  371.303834] scsi_runtime_resume
[  371.307007] scsi_runtime_resume
[  371.310213] sd 0:0:0:0: [sda] tag#0 device offline or changed
[  371.316011] blk_update_request: I/O error, dev sda, sector 5101888 op
0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[  372.560690] scsi_runtime_suspend
[  372.563968] scsi_runtime_suspend
[  372.567237] scsi_runtime_suspend

thanks Alan for taking the time and trying to fix this! you're close.
what is missing?

                                martin

  parent 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 [this message]
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
2020-07-29 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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