[PATCH v2] drm: Copy drm_wait_vblank to user before returning

[Michel Dänzer]

On 2021-08-12 9:49 p.m., Mark Yacoub wrote:
> From: Mark Yacoub <markyacoub at 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 at chromium.org>
> Change-Id: I98da279a5f1329c66a9d1e06b88d40b247b51313

With the Gerrit Change-Id removed,

Reviewed-by: Michel Dänzer <mdaenzer at redhat.com>


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer