From: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
To: "Christian König" <christian.koenig@amd.com>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org, matthew.auld@intel.com
Subject: Re: [RFC PATCH 1/2] dma-fence: Avoid establishing a locking order between fence classes
Date: Tue, 30 Nov 2021 13:56:13 +0100 [thread overview]
Message-ID: <57df8b0b-1d65-155f-a9a6-8073bbd4f28f@linux.intel.com> (raw)
In-Reply-To: <52a7cf8c-59c7-fec0-2274-d19bdc505314@amd.com>
On 11/30/21 13:42, Christian König wrote:
> Am 30.11.21 um 13:31 schrieb Thomas Hellström:
>> [SNIP]
>>> Other than that, I didn't investigate the nesting fails enough to
>>> say I can accurately review this. :)
>>
>> Basically the problem is that within enable_signaling() which is
>> called with the dma_fence lock held, we take the dma_fence lock of
>> another fence. If that other fence is a dma_fence_array, or a
>> dma_fence_chain which in turn tries to lock a dma_fence_array we hit
>> a splat.
>
> Yeah, I already thought that you constructed something like that.
>
> You get the splat because what you do here is illegal, you can't mix
> dma_fence_array and dma_fence_chain like this or you can end up in a
> stack corruption.
Hmm. Ok, so what is the stack corruption, is it that the
enable_signaling() will end up with endless recursion? If so, wouldn't
it be more usable we break that recursion chain and allow a more general
use?
Also what are the mixing rules between these? Never use a
dma-fence-chain as one of the array fences and never use a
dma-fence-array as a dma-fence-chain fence?
/Thomas
>
> Regards,
> Christian.
>
>>
>> But I'll update the commit message with a typical splat.
>>
>> /Thomas
>
next prev parent reply other threads:[~2021-11-30 12:56 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-30 12:19 [RFC PATCH 0/2] Attempt to avoid dma-fence-[chain|array] lockdep splats Thomas Hellström
2021-11-30 12:19 ` [RFC PATCH 1/2] dma-fence: Avoid establishing a locking order between fence classes Thomas Hellström
2021-11-30 12:25 ` Maarten Lankhorst
2021-11-30 12:31 ` Thomas Hellström
2021-11-30 12:42 ` Christian König
2021-11-30 12:56 ` Thomas Hellström [this message]
2021-11-30 13:26 ` Christian König
2021-11-30 14:35 ` Thomas Hellström
2021-11-30 15:02 ` Christian König
2021-11-30 18:12 ` Thomas Hellström
2021-11-30 19:27 ` Thomas Hellström
2021-12-01 7:05 ` Christian König
2021-12-01 8:23 ` [Linaro-mm-sig] " Thomas Hellström (Intel)
2021-12-01 8:36 ` Christian König
2021-12-01 10:15 ` Thomas Hellström (Intel)
2021-12-01 10:32 ` Christian König
2021-12-01 11:04 ` Thomas Hellström (Intel)
2021-12-01 11:25 ` Christian König
2021-12-01 12:16 ` Thomas Hellström (Intel)
2021-12-03 13:08 ` Christian König
2021-12-03 14:18 ` Thomas Hellström
2021-12-03 14:26 ` Christian König
2021-12-03 14:50 ` Thomas Hellström
2021-12-03 15:00 ` Christian König
2021-12-03 15:13 ` Thomas Hellström (Intel)
2021-12-07 18:08 ` [Intel-gfx] " Daniel Vetter
2021-12-07 20:46 ` Thomas Hellström
2021-12-20 9:37 ` Daniel Vetter
2021-11-30 12:32 ` Thomas Hellström
2021-11-30 12:19 ` [RFC PATCH 2/2] dma-fence: Avoid excessive recursive fence locking from enable_signaling() callbacks Thomas Hellström
2021-11-30 12:36 ` [RFC PATCH 0/2] Attempt to avoid dma-fence-[chain|array] lockdep splats Christian König
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