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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: Sat, 29 Aug 2020 18:33:26 +0200
Message-ID: <6d22ec22-a0c7-6a9d-439e-38ef87b0207c@puri.sm> (raw)
In-Reply-To: <20200829152635.GA498519@rowland.harvard.edu>

On 29.08.20 17:26, Alan Stern wrote:
> On Sat, Aug 29, 2020 at 09:24:30AM +0200, Martin Kepplinger wrote:
>> On 27.08.20 22:29, Alan Stern wrote:
>>> Instead, look at sd_resume().  That routine calls __scsi_execute() 
>>> indirectly through sd_start_stop_device(), and the only reason it does 
>>> this is because the sdkp->device->manage_start_stop flag is set.  You 
>>> ought to be able to clear this flag in sysfs, by writing to 
>>> /sys/block/sda/device/scsi_disk/*/manage_start_stop.  If you do this 
>>> before allowing the card reader to go into runtime suspend, does it then 
>>> resume okay?
>>
>> manage_start_stop in sysfs is 0 here.
> 
> Hmmm.  I'm wondering about something you wrote back in June 
> (https://marc.info/?l=linux-scsi&m=159345778431615&w=2):
> 
> 	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".
> 
> blk_queue_enter() would always set success to be true because pm 
> (derived from the BLK_MQ_REQ_PREEMPT flag) is true.  But why was the 
> BLK_MQ_REQ_PREEMPT flag set?  In other words, where was 
> blk_queue_enter() called from?
> 
> Can you get a stack trace (i.e., call dump_stack()) at exactly this 
> point, that is, when pm is true and q->rpm_status is RPM_SUSPENDED?  Or 
> do you already know the answer?
> 
>

I reverted any scsi/block out-of-tree fixes for this.

when I try to mount, pm is TRUE (BLK_MQ_REQ_PREEMT set) and that's the
first stack trace I get in this condition, inside of blk_queue_enter():

There is more, but I don't know if that's interesting.

[   38.642202] CPU: 2 PID: 1522 Comm: mount Not tainted 5.8.0-1-librem5 #487
[   38.642207] Hardware name: Purism Librem 5r3 (DT)
[   38.642213] Call trace:
[   38.642233]  dump_backtrace+0x0/0x210
[   38.642242]  show_stack+0x20/0x30
[   38.642252]  dump_stack+0xc8/0x128
[   38.642262]  blk_queue_enter+0x1b8/0x2d8
[   38.642271]  blk_mq_alloc_request+0x54/0xb0
[   38.642277]  blk_get_request+0x34/0x78
[   38.642286]  __scsi_execute+0x60/0x1c8
[   38.642291]  scsi_test_unit_ready+0x88/0x118
[   38.642298]  sd_check_events+0x110/0x158
[   38.642306]  disk_check_events+0x68/0x188
[   38.642312]  disk_clear_events+0x84/0x198
[   38.642320]  check_disk_change+0x38/0x90
[   38.642325]  sd_open+0x60/0x148
[   38.642330]  __blkdev_get+0xcc/0x4c8
[   38.642335]  __blkdev_get+0x278/0x4c8
[   38.642339]  blkdev_get+0x128/0x1a8
[   38.642345]  blkdev_open+0x98/0xb0
[   38.642354]  do_dentry_open+0x130/0x3c8
[   38.642359]  vfs_open+0x34/0x40
[   38.642366]  path_openat+0xa30/0xe40
[   38.642372]  do_filp_open+0x84/0x100
[   38.642377]  do_sys_openat2+0x1f4/0x2b0
[   38.642382]  do_sys_open+0x60/0xa8
(...)

and of course it doesn't work and /dev/sda1 disappears, see the initial
discussion that led to your fix.

  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
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 [this message]
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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