linux-kernel - Re: [PATCH v3 0/2] drm: Add GPU reset sysfs

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Date:   Wed, 30 Nov 2022 12:23:35 -0300
From:   André Almeida <andrealmeid@...lia.com>
To:     Simon Ser <contact@...rsion.fr>,
        Pekka Paalanen <ppaalanen@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, kernel-dev@...lia.com,
        alexander.deucher@....com, contactshashanksharma@...il.com,
        amaranath.somalapuram@....com, christian.koenig@....com,
        pierre-eric.pelloux-prayer@....com,
        Rob Clark <robdclark@...il.com>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Daniel Stone <daniel@...ishbar.org>,
        'Marek Olšák' <maraeo@...il.com>,
        Dave Airlie <airlied@...il.com>,
        "Pierre-Loup A . Griffais" <pgriffais@...vesoftware.com>
Subject: Re: [PATCH v3 0/2] drm: Add GPU reset sysfs

On 11/28/22 06:30, Simon Ser wrote:
> The PID is racy, the user-space daemon could end up killing an
> unrelated process… Is there any way we could use a pidfd instead?

Is the PID race condition something that really happens or rather 
something theoretical?

Anyway, I can't see how pidfd and uevent would work together. Since 
uevent it's kind of a broadcast and pidfd is an anon file, it wouldn't 
be possible to say to userspace which is the fd to be used giving that 
file descriptors are per process resources.

On the other hand, this interface could be converted to be an ioctl that 
userspace would block waiting for a reset notification, then the kernel 
could create a pidfd and give to the blocked process the right fd. We 
would probably need a queue to make sure no event is lost.

Thanks
	André