Hi Maíra,
Am 28.12.22 um 20:49 schrieb Maíra Canal:
Hi Stefan,
I was able to reproduce this error on drm-misc-next. I bisected,
and I got into commit 6bed2ea3cb38. I noticed that the crtc->mutex is
being locked twice, and this might be causing the problem. I wrote a
patch to try to fix this issue, and after applying the patch, I wasn't
able to reproduce the error anymore.
Let me know if you were able to reproduce the warning after applying
this patch.
the patch works as expected and avoid the warning. I tested it on top of
v6.1 with RPi 3 B+ and RPi 4 B.
In case you send the patch please add the Fixes tag so the patch get
backported to stable.
Thanks a lot
Stefan
Best Regards,
- Maíra Canal
---
From f6c910327d060e2314947e7e456db363a6164a49 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ma=C3=ADra=20Canal?= <mcanal@xxxxxxxxxx>
Date: Wed, 28 Dec 2022 16:14:34 -0300
Subject: [PATCH] drm/vc4: don't lock crtc's mutex on reset link
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Current, crtc->mutex is being locked twice: first, by
vc4_hdmi_reset_link() and them, internally, by
drm_atomic_get_crtc_state(). This produces the following output when
PROVE_LOCKING is enabled:
[ 825.612809] ------------[ cut here ]------------
[ 825.612852] WARNING: CPU: 1 PID: 116 at
drivers/gpu/drm/drm_modeset_lock.c:276
drm_modeset_drop_locks+0x60/0x68 [drm]
[ 825.613458] Modules linked in: 8021q mrp garp stp llc
raspberrypi_cpufreq brcmfmac brcmutil crct10dif_ce hci_uart cfg80211
btqca btbcm bluetooth vc4 raspberrypi_hwmon snd_soc_hdmi_codec cec
clk_raspberrypi ecdh_generic drm_display_helper ecc rfkill
drm_dma_helper drm_kms_helper pwm_bcm2835 bcm2835_thermal bcm2835_rng
rng_core i2c_bcm2835 drm fuse ip_tables x_tables ipv6
[ 825.613735] CPU: 1 PID: 116 Comm: kworker/1:2 Tainted: G W
6.1.0-rc6-01399-g941aae326315 #3
[ 825.613759] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
[ 825.613777] Workqueue: events output_poll_execute [drm_kms_helper]
[ 825.614038] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 825.614063] pc : drm_modeset_drop_locks+0x60/0x68 [drm]
[ 825.614603] lr : drm_helper_probe_detect+0x120/0x1b4 [drm_kms_helper]
[ 825.614829] sp : ffff800008313bf0
[ 825.614844] x29: ffff800008313bf0 x28: ffffcd7778b8b000 x27:
0000000000000000
[ 825.614883] x26: 0000000000000001 x25: 0000000000000001 x24:
ffff677cc35c2758
[ 825.614920] x23: ffffcd7707d01430 x22: ffffcd7707c3edc7 x21:
0000000000000001
[ 825.614958] x20: 0000000000000000 x19: ffff800008313c10 x18:
000000000000b6d3
[ 825.614995] x17: ffffcd777835e214 x16: ffffcd7777cef870 x15:
fffff81000000000
[ 825.615033] x14: 0000000000000000 x13: 0000000000000099 x12:
0000000000000002
[ 825.615070] x11: 72917988020af800 x10: 72917988020af800 x9 :
72917988020af800
[ 825.615108] x8 : ffff677cc665e0a8 x7 : d00a8c180000110c x6 :
ffffcd77774c0054
[ 825.615145] x5 : 0000000000000000 x4 : 0000000000000001 x3 :
0000000000000000
[ 825.615181] x2 : ffff677cc55e1880 x1 : ffffcd7777cef8ec x0 :
ffff800008313c10
[ 825.615219] Call trace:
[ 825.615232] drm_modeset_drop_locks+0x60/0x68 [drm]
[ 825.615773] drm_helper_probe_detect+0x120/0x1b4 [drm_kms_helper]
[ 825.616003] output_poll_execute+0xe4/0x224 [drm_kms_helper]
[ 825.616233] process_one_work+0x2b4/0x618
[ 825.616264] worker_thread+0x24c/0x464
[ 825.616288] kthread+0xec/0x110
[ 825.616310] ret_from_fork+0x10/0x20
[ 825.616335] irq event stamp: 7634
[ 825.616349] hardirqs last enabled at (7633): [<ffffcd777831ee90>]
_raw_spin_unlock_irq+0x3c/0x78
[ 825.616384] hardirqs last disabled at (7634): [<ffffcd7778315a78>]
__schedule+0x134/0x9f0
[ 825.616411] softirqs last enabled at (7630): [<ffffcd7707aacea0>]
local_bh_enable+0x4/0x30 [ipv6]
[ 825.617019] softirqs last disabled at (7618): [<ffffcd7707aace70>]
local_bh_disable+0x4/0x30 [ipv6]
[ 825.617586] ---[ end trace 0000000000000000 ]---
So, don't lock crtc->mutex inside the driver and let the right lock be
automatically acquired by drm_atomic_get_crtc_state().
Reported-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
---
drivers/gpu/drm/vc4/vc4_hdmi.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c
b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 0d3313c71f2f..b3b1958b5f4d 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -340,10 +340,6 @@ static int vc4_hdmi_reset_link(struct
drm_connector *connector,
if (!crtc)
return 0;
- ret = drm_modeset_lock(&crtc->mutex, ctx);
- if (ret)
- return ret;
-
crtc_state = crtc->state;
if (!crtc_state->active)
return 0;
