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

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Message-ID: <87senhoq1k.fsf@intel.com>
Date: Wed, 12 Mar 2025 15:13:59 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Nathan Lynch <nathan.lynch@....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

Hi Nathan,

Nathan Lynch <nathan.lynch@....com> writes:

> Hi,
>
> Vinicius Costa Gomes <vinicius.gomes@...el.com> writes:
>> Change the "wait for operation finish" logic to take interrupts into
>> account.
>>
>> When using dmatest with idxd DMA engine, it's possible that during
>> longer tests, the interrupt notifying the finish of an operation
>> happens during wait_event_freezable_timeout(), which causes dmatest to
>> cleanup all the resources, some of which might still be in use.
>>
>> This fix ensures that the wait logic correctly handles interrupts,
>> preventing premature cleanup of resources.
>>
>> Reported-by: kernel test robot <oliver.sang@...el.com>
>> Closes: https://lore.kernel.org/oe-lkp/202502171134.8c403348-lkp@intel.com
>
> Given the report at the URL above I'm struggling to follow the rationale
> for this change. It looks like a use-after-free in idxd while
> resetting/unbinding the device, and I can't see how changing whether
> dmatest threads perform freezeable waits would change this.
>

I think that the short version is that the reproducition script triggers
different problems on different platforms/configurations.

The solution I proposed fixes a problem I was seeing on a SPR system, on
a GNR system (that I was only able to get later) I see something more similar
to this particular splat (currently working on the fix).

Seeing this question, I realize that I should have added a note to the
commit detailing this.

So I am planning on proposing two (this and another) fixes for the same
report, hoping that it's not that confusing/unusual.


Cheers,
-- 
Vinicius