leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

drm/msm/kms: Make a lock_class_key for each crtc mutex

Browse Source 
Lockdep complains about an AA deadlock when rebooting the device.

base-commit: 19c329f680

============================================
WARNING: possible recursive locking detected
5.4.91 #1 Not tainted
--------------------------------------------
reboot/5213 is trying to acquire lock:
ffffff80d13391b0 (&kms->commit_lock[i]){+.+.}, at: lock_crtcs+0x60/0xa4

but task is already holding lock:
ffffff80d1339110 (&kms->commit_lock[i]){+.+.}, at: lock_crtcs+0x60/0xa4

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&kms->commit_lock[i]);
lock(&kms->commit_lock[i]);

*** DEADLOCK ***

May be due to missing lock nesting notation

6 locks held by reboot/5213:
__arm64_sys_reboot+0x148/0x2a0
device_shutdown+0x10c/0x2c4
drm_atomic_helper_shutdown+0x48/0xfc
modeset_lock+0x120/0x24c
lock_crtcs+0x60/0xa4

stack backtrace:
CPU: 4 PID: 5213 Comm: reboot Not tainted 5.4.91 #1
Hardware name: Google Pompom (rev1) with LTE (DT)
Call trace:
dump_backtrace+0x0/0x1dc
show_stack+0x24/0x30
dump_stack+0xfc/0x1a8
__lock_acquire+0xcd0/0x22b8
lock_acquire+0x1ec/0x240
__mutex_lock_common+0xe0/0xc84
mutex_lock_nested+0x48/0x58
lock_crtcs+0x60/0xa4
msm_atomic_commit_tail+0x348/0x570
commit_tail+0xdc/0x178
drm_atomic_helper_commit+0x160/0x168
drm_atomic_commit+0x68/0x80

This is because lockdep thinks all the locks taken in lock_crtcs() are
the same lock, when they actually aren't. That's because we call
mutex_init() in msm_kms_init() and that assigns one static key for every
lock initialized in this loop. Let's allocate a dynamic number of
lock_class_keys and assign them to each lock so that lockdep can figure
out an AA deadlock isn't possible here.

Fixes: b3d91800d9 ("drm/msm: Fix race condition in msm driver with async layer updates")
Cc: Krishna Manikandan <mkrishn@codeaurora.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
This commit is contained in:
Stephen Boyd 2021-01-28 09:09:29 -08:00 committed by Rob Clark
parent 555c50a4a1
commit 6ec9351809
1 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/gpu/drm/msm/msm_kms.h
View File

@ -157,6 +157,7 @@ struct msm_kms {
* from the crtc's pending_timer close to end of the frame:
*/
struct mutex commit_lock[MAX_CRTCS];
struct lock_class_key commit_lock_keys[MAX_CRTCS];
unsigned pending_crtc_mask;
struct msm_pending_timer pending_timers[MAX_CRTCS];
};
@ -166,8 +167,11 @@ static inline int msm_kms_init(struct msm_kms *kms,
{
unsigned i, ret;
for (i = 0; i < ARRAY_SIZE(kms->commit_lock); i++)
mutex_init(&kms->commit_lock[i]);
for (i = 0; i < ARRAY_SIZE(kms->commit_lock); i++) {
lockdep_register_key(&kms->commit_lock_keys[i]);
__mutex_init(&kms->commit_lock[i], "&kms->commit_lock[i]",
&kms->commit_lock_keys[i]);
}
kms->funcs = funcs;