linux-kernel - Re: [PATCH] drm: fb-helper: Avoid nesting spinlock_t into raw_spinlock

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Date:   Wed, 16 Feb 2022 08:40:45 +0100
From:   Sebastian Siewior <bigeasy@...utronix.de>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: fb-helper: Avoid nesting spinlock_t into
 raw_spinlock_t

On 2022-02-15 20:59:24 [+0100], Jiri Kosina wrote:
> Thanks for confirmation, seems like this problem is indeed cured by your 
> series.

Oki.

> I still believe though that we shouldn't let 5.17 released with this 
> warning being emitted into dmesg, so I'd suggest going with my patch for 
> mainline, and revert it in your series on top of it.

No. That warning is only visible with CONFIG_PROVE_RAW_LOCK_NESTING with
the following paragraph in its help:
|   NOTE: There are known nesting problems. So if you enable this
|   option expect lockdep splats until these problems have been fully
|   addressed which is work in progress. This config switch allows to
|   identify and analyze these problems. It will be removed and the
|   check permanently enabled once the main issues have been fixed.

This warning in this call chain should affect every console driver which
acquires a lock.

> Thanks,

Sebastian