Re: [PATCH 6.18.y 0/5] drm/vkms: Backport generic vblank timer to fix ABBA deadlock

[Sasha Levin]

> [PATCH 6.18.y 0/5] drm/vkms: Backport generic vblank timer to fix ABBA deadlock
>
> 1/5 drm/vblank: Add vblank timer (74afeb812850)
> 2/5 drm/vblank: Add CRTC helpers for simple use cases (d54dbb5963bd)
> 3/5 drm/vkms: Convert to DRM's vblank timer (02e2681ffe1a)
> 4/5 drm/atomic: Increase timeout in drm_atomic_helper_wait_for_vblanks() (79ae8510b5b8)
> 5/5 drm/vblank: Fix kernel docs for vblank timer (3946d3ba9934)

Thanks for putting this together.

Looking at the five commits:

  - 1/5 (74afeb812850) is the one that actually fixes the ABBA
    deadlock you observed under Syzkaller; it adds the generic vblank
    timer that replaces the open-coded vkms hrtimer path.

  - 2/5 (d54dbb5963bd) adds new CRTC helpers for "simple use cases".
    No Fixes:/Cc:stable, no described bug.

  - 3/5 (02e2681ffe1a) is a refactor that converts vkms to the new
    helpers. No Fixes:/Cc:stable, no described bug.

  - 4/5 (79ae8510b5b8) is a v7.1-rc1 timeout bump that depends on 1/5.
    It is not yet in any released stable, so applying it to 6.18.y
    would put it on an LTS before any LTS contains it.

  - 5/5 (3946d3ba9934) is a doc fix for 1/5.

Per stable-kernel-rules, what I need to queue is the minimum set that
fixes the bug. Could you explain, per patch, why 2/5..5/5 are required
to make 1/5 work / are required to actually fix the deadlock? If only
1/5 is needed, please resend just that one with your Signed-off-by
added (the carried patches today only have Thomas's S-o-b, which
breaks the chain of custody on a stable submission).

--
Thanks,
Sasha