linux-kernel - Re: [PATCH v1 5/7] Revert "drm: Assert held reservation lock for dma-buf mmapping"

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Message-ID: <91788325-5050-9cf8-9246-5496d9db4df3@collabora.com>
Date:   Wed, 5 Apr 2023 03:33:22 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Christian König <christian.koenig@....com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Liam Mark <lmark@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <jstultz@...gle.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tomi Valkeinen <tomba@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Emil Velikov <emil.l.velikov@...il.com>
Cc:     linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        linux-tegra@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v1 5/7] Revert "drm: Assert held reservation lock for
 dma-buf mmapping"

On 4/3/23 18:17, Christian König wrote:
> Am 02.04.23 um 18:48 schrieb Dmitry Osipenko:
>> Don't assert held dma-buf reservation lock on memory mapping of exported
>> buffer.
>>
>> We're going to change dma-buf mmap() locking policy such that exporters
>> will have to handle the lock. The previous locking policy caused deadlock
>> problem for DRM drivers in a case of self-imported dma-bufs, it's solved
>> by moving the lock down to exporters.
> 
> I only checked the TTM code path and think that at least that one should
> work fine.
> 
>> Fixes: 39ce25291871 ("drm: Assert held reservation lock for dma-buf
>> mmapping")
> 
> This here is not really a "fix" for the previous patch. We just found
> that we didn't like the behavior and so reverted the original patch.
> 
> A "Reverts..." comment in the commit message would be more appropriate I
> think.

Ack, will drop the fixes tag in v2. Thank you and Emil for the review.

-- 
Best regards,
Dmitry