On 10/3/23 17:18, Petr Tesařík wrote:
On Tue, 3 Oct 2023 14:57:46 +0200
"Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:
On Tue, Oct 3, 2023 at 2:51 PM Petr Tesařík <petr@xxxxxxxxxxx> wrote:
On Tue, 3 Oct 2023 14:48:13 +0200
"Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:
On Tue, Oct 3, 2023 at 2:40 PM Petr Tesařík <petr@xxxxxxxxxxx> wrote:
On Tue, 3 Oct 2023 14:34:56 +0200
"Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:
On Tue, Oct 3, 2023 at 1:02 PM Petr Tesařík <petr@xxxxxxxxxxx> wrote:
On Tue, 3 Oct 2023 12:15:10 +0200
"Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:
On Tue, Oct 3, 2023 at 11:31 AM Petr Tesařík <petr@xxxxxxxxxxx> wrote:
Hi again (adding more recipients),
On Sat, 30 Sep 2023 12:20:54 +0200
Petr Tesařík <petr@xxxxxxxxxxx> wrote:
Hi all,
this time no patch (yet). In short, my Thinkpad running v6.6-rc3 fails
to resume from S3. It also fails the same way with Tumbleweed v6.5
kernel. I was able to capture a crash dump of the v6.5 kernel, and
here's my analysis:
The system never gets to waking up my SATA SSD disk:
[0:0:0:0] disk ATA KINGSTON SEDC600 H5.1 /dev/sda
There is a pending resume work for kworker/u32:12 (PID 11032), but this
worker is stuck in 'D' state:
prog.stack_trace(11032)
#0 context_switch (../kernel/sched/core.c:5381:2)
#1 __schedule (../kernel/sched/core.c:6710:8)
#2 schedule (../kernel/sched/core.c:6786:3)
#3 schedule_preempt_disabled (../kernel/sched/core.c:6845:2)
#4 __mutex_lock_common (../kernel/locking/mutex.c:679:3)
#5 __mutex_lock (../kernel/locking/mutex.c:747:9)
#6 acpi_device_hotplug (../drivers/acpi/scan.c:382:2)
#7 acpi_hotplug_work_fn (../drivers/acpi/osl.c:1162:2)
#8 process_one_work (../kernel/workqueue.c:2600:2)
#9 worker_thread (../kernel/workqueue.c:2751:4)
#10 kthread (../kernel/kthread.c:389:9)
#11 ret_from_fork (../arch/x86/kernel/process.c:145:3)
#12 ret_from_fork_asm+0x1b/0x20 (../arch/x86/entry/entry_64.S:304)
acpi_device_hotplug() tries to acquire acpi_scan_lock, which is held by
systemd-sleep (PID 11002). This task is also in 'D' state:
prog.stack_trace(11002)
#0 context_switch (../kernel/sched/core.c:5381:2)
#1 __schedule (../kernel/sched/core.c:6710:8)
#2 schedule (../kernel/sched/core.c:6786:3)
#3 schedule_preempt_disabled (../kernel/sched/core.c:6845:2)
#4 __mutex_lock_common (../kernel/locking/mutex.c:679:3)
#5 __mutex_lock (../kernel/locking/mutex.c:747:9)
#6 device_lock (../include/linux/device.h:958:2)
#7 device_complete (../drivers/base/power/main.c:1063:2)
#8 dpm_complete (../drivers/base/power/main.c:1121:3)
#9 suspend_devices_and_enter (../kernel/power/suspend.c:516:2)
I believe the issue must be somewhere here. The whole suspend and
resume logic in suspend_devices_and_enter() is framed by
platform_suspend_begin() and platform_resume_end().
My system is an ACPI system, so suspend_ops contains:
.begin = acpi_suspend_begin,
.end = acpi_pm_end,
Now, acpi_suspend_begin() acquires acpi_scan_lock through
acpi_pm_start(), and the lock is not released until acpi_pm_end().
Since dpm_complete() waits for the completion of a work that tries to
acquire acpi_scan_lock, the system will deadlock.
So holding acpi_scan_lock across suspend-resume is basically to
prevent the hotplug from taking place then IIRC.
AFAICS either:
a. the ACPI lock cannot be held while dpm_complete() runs, or
b. ata_scsi_dev_rescan() must not be scheduled before the system is
resumed, or
c. acpi_device_hotplug() must be implemented without taking dev->mutex.
My gut feeling is that b. is the right answer.
It's been a while since I looked at that code last time, but then it
has not changed for quite some time too.
It looks like the acpi_device_hotplug() path attempts to acquire
acpi_scan_lock() while holding dev->mutex which is kind of silly. I
need to check that, though.
Thanks for your willingness. Well, it's not quite what you describe. If
it was a simple ABBA deadlock, then it would be reported by lockdep.
No, it's more complicated:
1. suspend_devices_and_enter() holds acpi_scan_lock,
2. an ACPI hotplug work runs, but acpi_device_hotplug() goes to sleep
when it gets to acquiring acpi_scan_lock,
3. ata_scsi_dev_rescan() submits a SCSI command and waits for its
completion while holding dev->mutex,
4. the SCSI completion work happens to be put on the same workqueue as
the ACPI hotplug work in step 2,
^^^--- THIS is how the two events are serialized!
Which is unexpected.
And quite honestly I'm not sure how this can happen, because
acpi_hotplug_schedule() uses a dedicated workqueue and it is called
from (a) the "eject" sysfs attribute (which cannot happen while system
suspend-resume is in progress) and (b) acpi_bus_notify() which has
nothing to do with SCSI.
Oh, you're right, and I was too quick. They cannot be on the same
queue...
Maybe the workqueue used for the SCSI completion is freezable?
Yes, that's it:
*(struct workqueue_struct *)0xffff97d240b2fe00 = {
/* ... */
.flags = (unsigned int)4,
/* WQ_FREEZABLE = 1 << 2 */
Good. But if this workqueue is frozen, the system still cannot make
progress.
The problem seems to be that dev->mutex is held while the work item
goes to a freezable workqueue and is waited for, which is an almost
guaranteed deadlock scenario.
Ah. Thanks for explanation and direction! I'm going to dive into the
block layer and/or SCSI code and bug other people with my findings.
Please feel free to CC me on that in case I can help.
And here I am again... The frozen workqueue is in fact pm_wq, and the
work item that is waited for is pm_runtime_work. The block layer calls
pm_request_resume() on the device to resume the queue.
I bet the queue should not be resumed this early. In fact, it seems
that this is somewhat known to the ATA developers, because
ata_scsi_dev_rescan() contains this beautiful comment and code:
/*
* If the rescan work was scheduled because of a resume
* event, the port is already fully resumed, but the
* SCSI device may not yet be fully resumed. In such
* case, executing scsi_rescan_device() may cause a
* deadlock with the PM code on device_lock(). Prevent
* this by giving up and retrying rescan after a short
* delay.
*/
delay_rescan = sdev->sdev_gendev.power.is_suspended;
if (delay_rescan) {
scsi_device_put(sdev);
break;
}
It just doesn't seem to work as expected, at least not in my case.
Did you test the libata suspend/resume patches from Damien?
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman
