This is a note to let you know that I've just added the patch titled
drm: Don't unref the same fb many times by mistake due to deadlock handling
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-don-t-unref-the-same-fb-many-times-by-mistake-due-to-deadlock-handling.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cb4daf271302d71a6b9a7c01bd0b6d76febd8f0c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@xxxxxxxxxxxxxxx>
Date: Mon, 11 Dec 2023 10:16:24 +0200
Subject: drm: Don't unref the same fb many times by mistake due to deadlock handling
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
commit cb4daf271302d71a6b9a7c01bd0b6d76febd8f0c upstream.
If we get a deadlock after the fb lookup in drm_mode_page_flip_ioctl()
we proceed to unref the fb and then retry the whole thing from the top.
But we forget to reset the fb pointer back to NULL, and so if we then
get another error during the retry, before the fb lookup, we proceed
the unref the same fb again without having gotten another reference.
The end result is that the fb will (eventually) end up being freed
while it's still in use.
Reset fb to NULL once we've unreffed it to avoid doing it again
until we've done another fb lookup.
This turned out to be pretty easy to hit on a DG2 when doing async
flips (and CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y). The first symptom I
saw that drm_closefb() simply got stuck in a busy loop while walking
the framebuffer list. Fortunately I was able to convince it to oops
instead, and from there it was easier to track down the culprit.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20231211081625.25704-1-ville.syrjala@xxxxxxxxxxxxxxx
Acked-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_plane.c | 1 +
1 file changed, 1 insertion(+)
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -1183,6 +1183,7 @@ retry:
out:
if (fb)
drm_framebuffer_put(fb);
+ fb = NULL;
if (plane->old_fb)
drm_framebuffer_put(plane->old_fb);
plane->old_fb = NULL;
Patches currently in stable-queue which might be from ville.syrjala@xxxxxxxxxxxxxxx are
queue-4.19/drm-don-t-unref-the-same-fb-many-times-by-mistake-due-to-deadlock-handling.patch
