From: "Michel Dänzer" <michel@daenzer.net>
To: Mark Yacoub <markyacoub@chromium.org>, dri-devel@lists.freedesktop.org
Cc: seanpaul@chromium.org, abhinavk@codeaurora.org,
robdclark@chromium.org, airlied@linux.ie,
Mark Yacoub <markyacoub@google.com>
Subject: Re: [PATCH v2] drm: Copy drm_wait_vblank to user before returning
Date: Fri, 13 Aug 2021 09:32:56 +0200 [thread overview]
Message-ID: <4ab4548f-34fc-27cb-928e-af2b8ab78b1b@daenzer.net> (raw)
In-Reply-To: <20210812194917.1703356-1-markyacoub@chromium.org>
On 2021-08-12 9:49 p.m., Mark Yacoub wrote:
> From: Mark Yacoub <markyacoub@google.com>
>
> [Why]
> Userspace should get back a copy of drm_wait_vblank that's been modified
> even when drm_wait_vblank_ioctl returns a failure.
>
> Rationale:
> drm_wait_vblank_ioctl modifies the request and expects the user to read
> it back. When the type is RELATIVE, it modifies it to ABSOLUTE and updates
> the sequence to become current_vblank_count + sequence (which was
> RELATIVE), but now it became ABSOLUTE.
> drmWaitVBlank (in libdrm) expects this to be the case as it modifies
> the request to be Absolute so it expects the sequence to would have been
> updated.
>
> The change is in compat_drm_wait_vblank, which is called by
> drm_compat_ioctl. This change of copying the data back regardless of the
> return number makes it en par with drm_ioctl, which always copies the
> data before returning.
>
> [How]
> Return from the function after everything has been copied to user.
>
> Fixes: IGT:kms_flip::modeset-vs-vblank-race-interruptible
> Tested on ChromeOS Trogdor(msm)
>
> Signed-off-by: Mark Yacoub <markyacoub@chromium.org>
> Change-Id: I98da279a5f1329c66a9d1e06b88d40b247b51313
With the Gerrit Change-Id removed,
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and X developer
next prev parent reply other threads:[~2021-08-13 7:33 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 17:55 [PATCH] drm: Copy drm_wait_vblank request and copy_to_user before return Mark Yacoub
2021-08-12 9:26 ` Michel Dänzer
2021-08-12 19:51 ` Mark Yacoub
2021-08-12 19:49 ` [PATCH v2] drm: Copy drm_wait_vblank to user before returning Mark Yacoub
2021-08-13 7:32 ` Michel Dänzer [this message]
2021-08-13 15:48 ` Mark Yacoub
2021-08-17 17:59 ` Sean Paul
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