linux-kernel - Atomicity in KMS panic notifier

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Date:	Mon, 05 May 2014 15:02:09 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	dri-devel@...ts.freedesktop.org
Cc:	linux-kernel@...r.kernel.org
Subject: Atomicity in KMS panic notifier

Hi,

while debugging a few reported bugs, I noticed that
drm_fb_helper_force_kernel_mode() that is called in the KMS panic
notifier isn't really atomic-safe.  It invokes crtc's set_config(),
and all implementations seem to involve with page allocations (kmalloc
with GFP_KERNEL, via some ttm ops, etc).  I've actually seen the Oops
with cirrus KMS during panic due to this.

Does anyone have an idea to fix this?  I thought of re-using
drm_fb_helper_debug_enter(), but this won't work with many drivers
that don't have crtc->mode_set_base_atomic(), either (yeah, this is
another bug).

thanks,

Takashi
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