linux-kernel - Re: [PATCH] PM: hibernate: Freeze kernel threads in software

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Message-ID: <08f28683-4978-3e3c-e85a-303f6e46ef55@acm.org>
Date:   Sun, 26 Apr 2020 11:33:56 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>, decui@...rosoft.com
Cc:     linux-pm@...r.kernel.org, len.brown@...el.com, pavel@....cz,
        mikelley@...rosoft.com, longli@...rosoft.com,
        linux-kernel@...r.kernel.org, ming.lei@...hat.com,
        wei.liu@...nel.org, sthemmin@...rosoft.com, haiyangz@...rosoft.com,
        kys@...rosoft.com, stable@...r.kernel.org
Subject: Re: [PATCH] PM: hibernate: Freeze kernel threads in software_resume()

On 2020-04-26 09:24, Rafael J. Wysocki wrote:
> On Friday, April 24, 2020 5:40:16 AM CEST Dexuan Cui wrote:
>> Currently the kernel threads are not frozen in software_resume(), so
>> between dpm_suspend_start(PMSG_QUIESCE) and resume_target_kernel(),
>> system_freezable_power_efficient_wq can still try to submit SCSI
>> commands and this can cause a panic since the low level SCSI driver
>> (e.g. hv_storvsc) has quiesced the SCSI adapter and can not accept
>> any SCSI commands: https://lkml.org/lkml/2020/4/10/47
>>
>> At first I posted a fix (https://lkml.org/lkml/2020/4/21/1318) trying
>> to resolve the issue from hv_storvsc, but with the help of
>> Bart Van Assche, I realized it's better to fix software_resume(),
>> since this looks like a generic issue, not only pertaining to SCSI.
>>
>> Cc: Bart Van Assche <bvanassche@....org>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
>> ---
>>  kernel/power/hibernate.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index 86aba8706b16..30bd28d1d418 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -898,6 +898,13 @@ static int software_resume(void)
>>  	error = freeze_processes();
>>  	if (error)
>>  		goto Close_Finish;
>> +
>> +	error = freeze_kernel_threads();
>> +	if (error) {
>> +		thaw_processes();
>> +		goto Close_Finish;
>> +	}
>> +
>>  	error = load_image_and_restore();
>>  	thaw_processes();
>>   Finish:
> 
> Applied as a fix for 5.7-rc4, thanks!

Hi Rafael,

What is not clear to me is how kernel threads are thawed after
load_image_and_restore() has finished? Should a comment perhaps be added
above the freeze_kernel_threads() call that explains how
thaw_kernel_threads() is invoked after load_image_and_restore() has
finished?

Thanks,

Bart.