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Subject: Re: [PATCH] PM: hibernate: Freeze kernel threads in software_resume()
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>, decui@microsoft.com
Cc:     linux-pm@vger.kernel.org, len.brown@intel.com, pavel@ucw.cz,
        mikelley@microsoft.com, longli@microsoft.com,
        linux-kernel@vger.kernel.org, ming.lei@redhat.com,
        wei.liu@kernel.org, sthemmin@microsoft.com, haiyangz@microsoft.com,
        kys@microsoft.com, stable@vger.kernel.org
References: <20200424034016.42046-1-decui@microsoft.com>
 <2420808.aENraY2TMt@kreacher>
From:   Bart Van Assche <bvanassche@acm.org>
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Date:   Sun, 26 Apr 2020 11:33:56 -0700
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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@acm.org>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Dexuan Cui <decui@microsoft.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.