linux-kernel - Re: [PATCH 1/2] PM: runtime: Fix I/O hang due to race between resume and runtime disable

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Message-ID: <CAJZ5v0jiLAgHCQ51cYqUX-xjir7ooAC3xKH9wMbwrebOEuxFdw@mail.gmail.com>
Date: Wed, 26 Nov 2025 20:16:38 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Bart Van Assche <bvanassche@....org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Yang Yang <yang.yang@...o.com>, Jens Axboe <axboe@...nel.dk>, 
	Pavel Machek <pavel@...nel.org>, Len Brown <lenb@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] PM: runtime: Fix I/O hang due to race between resume
 and runtime disable

On Wed, Nov 26, 2025 at 7:06 PM Bart Van Assche <bvanassche@....org> wrote:
>
> On 11/26/25 3:30 AM, Rafael J. Wysocki wrote:
> > On Wed, Nov 26, 2025 at 11:17 AM Yang Yang <yang.yang@...o.com> wrote:
> >>   T1:                                   T2:
> >>   blk_queue_enter
> >>   blk_pm_resume_queue
> >>   pm_request_resume
> >
> > Shouldn't this be pm_runtime_resume() rather?
>
> I tried to make that change on an Android device. As a result, the
> kernel complaint shown below appeared. My understanding is that sleeping
> in atomic context can trigger a deadlock and hence is not allowed.
>
> [   13.728890][    T1] WARNING: CPU: 6 PID: 1 at
> kernel/sched/core.c:9714 __might_sleep+0x78/0x84
> [   13.758800][    T1] Call trace:
> [   13.759027][    T1]  __might_sleep+0x78/0x84
> [   13.759340][    T1]  __pm_runtime_resume+0x40/0xb8
> [   13.759781][    T1]  __bio_queue_enter+0xc0/0x1cc
> [   13.760153][    T1]  blk_mq_submit_bio+0x884/0xadc
> [   13.760548][    T1]  __submit_bio+0x2c8/0x49c
> [   13.760879][    T1]  __submit_bio_noacct_mq+0x38/0x88
> [   13.761242][    T1]  submit_bio_noacct_nocheck+0x4fc/0x7b8
> [   13.761631][    T1]  submit_bio+0x214/0x4c0
> [   13.761941][    T1]  mpage_readahead+0x1b8/0x1fc
> [   13.762284][    T1]  blkdev_readahead+0x18/0x28
> [   13.762660][    T1]  page_cache_ra_unbounded+0x310/0x4d8
> [   13.763072][    T1]  page_cache_ra_order+0xc0/0x5b0
> [   13.763434][    T1]  page_cache_sync_ra+0x17c/0x268
> [   13.763782][    T1]  filemap_read+0x4c4/0x12f4
> [   13.764125][    T1]  blkdev_read_iter+0x100/0x164
> [   13.764475][    T1]  vfs_read+0x188/0x348
> [   13.764789][    T1]  __se_sys_pread64+0x84/0xc8
> [   13.765180][    T1]  __arm64_sys_pread64+0x1c/0x2c
> [   13.765556][    T1]  invoke_syscall+0x58/0xf0
> [   13.765876][    T1]  do_el0_svc+0x8c/0xe0
> [   13.766172][    T1]  el0_svc+0x50/0xd4
> [   13.766583][    T1]  el0t_64_sync_handler+0x20/0xf4
> [   13.766932][    T1]  el0t_64_sync+0x1bc/0x1c0
> [   13.767294][    T1] irq event stamp: 2589614
> [   13.767592][    T1] hardirqs last  enabled at (2589613):
> [<ffffffc0800eaf24>] finish_lock_switch+0x70/0x108
> [   13.768283][    T1] hardirqs last disabled at (2589614):
> [<ffffffc0814b66f4>] el1_dbg+0x24/0x80
> [   13.768875][    T1] softirqs last  enabled at (2589370):
> [<ffffffc080082a7c>] ____do_softirq+0x10/0x20
> [   13.769529][    T1] softirqs last disabled at (2589349):
> [<ffffffc080082a7c>] ____do_softirq+0x10/0x20
>
> I think that the filemap_invalidate_lock_shared() call in
> page_cache_ra_unbounded() forbids sleeping in submit_bio().

The wait_event() macro in __bio_queue_enter() calls might_sleep() at
the very beginning, so why would it not complain?

IIUC, this is the WARN_ONCE() in __might_sleep() about the task state
being different from TASK_RUNNING, which triggers because
prepare_to_wait_event() changes the task state to
TASK_UNINTERRUPTIBLE.

This means that calling pm_runtime_resume() cannot be part of the
wait_event() condition, so blk_pm_resume_queue() and the wait_event()
macros involving it would need some rewriting.