linux-kernel - Re: [PATCH v1] dmaengine: dmatest: Fix dmatest waiting less when interrupted

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Message-ID: <87y0x7z45p.fsf@AUSNATLYNCH.amd.com>
Date: Fri, 14 Mar 2025 16:35:46 -0500
From: Nathan Lynch <nathan.lynch@....com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>, Vinod Koul
	<vkoul@...nel.org>, <dmaengine@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC: <dave.jiang@...el.com>, <kristen.c.accardi@...el.com>, kernel test robot
	<oliver.sang@...el.com>
Subject: Re: [PATCH v1] dmaengine: dmatest: Fix dmatest waiting less when
 interrupted

Vinicius Costa Gomes <vinicius.gomes@...el.com> writes:
> Nathan Lynch <nathan.lynch@....com> writes:
>> Vinicius Costa Gomes <vinicius.gomes@...el.com> writes:
>>> My understanding (and testing) is that wait_event_timeout() will block
>>> for the duration even in the face of interrupts, 'freezable' will not.
>>
>> They have different behaviors with respect to *signals* and the
>> wake_up() variant used, but not device interrupts.
>>
>
> Ah! That's something that I wasn't considering. That it could be
> something other than interrupts that were unblocking wait_event_*().

Well, I doubt it would be a signal in this case. Maybe you've
experienced timeouts?

>> dmatest_callback() employs wake_up_all(), which means this change
>> introduces no beneficial difference in the wakeup behavior. The dmatest
>> thread gets woken on receipt of the completion interrupt either way.
>>
>> And to reiterate, the change regresses the combination of dmatest and
>> the task freezer, which is a use case people have cared about,
>> apparently.
>>
>
> If this change in behavior causes a regression for others, glad to send
> a revert and find another solution.

Thanks - yes it should be reverted or dropped IMO.