| Message ID | 1462266751-29123-1-git-send-email-maarten.lankhorst@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, May 03, 2016 at 11:12:31AM +0200, Maarten Lankhorst wrote: > When I was writing an atomic wrapper for rmfb, I ran into the > following backtrace from lockdep: > > ============================================= > [ INFO: possible recursive locking detected ] > 4.5.0-patser+ #4696 Tainted: G U > --------------------------------------------- > kworker/2:2/2608 is trying to acquire lock: > (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c9ddc>] drm_modeset_lock+0x7c/0x120 [drm] > > but task is already holding lock: > (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm] > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(crtc_ww_class_mutex); > lock(crtc_ww_class_mutex); > > *** DEADLOCK *** > > May be due to missing lock nesting notation > > 4 locks held by kworker/2:2/2608: > #0: ("events"){.+.+.+}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0 > #1: ((&arg.work)){+.+.+.}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0 > #2: (crtc_ww_class_acquire){+.+.+.}, at: [<ffffffffc004532a>] drm_atomic_helper_remove_fb+0x4a/0x1d0 [drm_kms_helper] > #3: (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm] > > While lockdep probably catches this bug when it happens, it's better > to explicitly warn when state->acquire_ctx is not set. > > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Yeah, because of the automagic fallback to normal mutex semantics when acquire_ctx == NULL in ww_mutex_lock this can go boom, and the lockdep splat is pretty hard to read. Makes sense to have an explicit WARN_ON about it. Applied to drm-misc, thanks. -Daniel > --- > drivers/gpu/drm/drm_atomic.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c > index 0b526423f19f..69adcf3944cc 100644 > --- a/drivers/gpu/drm/drm_atomic.c > +++ b/drivers/gpu/drm/drm_atomic.c > @@ -263,6 +263,8 @@ drm_atomic_get_crtc_state(struct drm_atomic_state *state, > int ret, index = drm_crtc_index(crtc); > struct drm_crtc_state *crtc_state; > > + WARN_ON(!state->acquire_ctx); > + > crtc_state = drm_atomic_get_existing_crtc_state(state, crtc); > if (crtc_state) > return crtc_state; > @@ -622,6 +624,8 @@ drm_atomic_get_plane_state(struct drm_atomic_state *state, > int ret, index = drm_plane_index(plane); > struct drm_plane_state *plane_state; > > + WARN_ON(!state->acquire_ctx); > + > plane_state = drm_atomic_get_existing_plane_state(state, plane); > if (plane_state) > return plane_state; > @@ -890,6 +894,8 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state, > struct drm_mode_config *config = &connector->dev->mode_config; > struct drm_connector_state *connector_state; > > + WARN_ON(!state->acquire_ctx); > + > ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx); > if (ret) > return ERR_PTR(ret); > -- > 2.5.5 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
============================================= [ INFO: possible recursive locking detected ] 4.5.0-patser+ #4696 Tainted: G U --------------------------------------------- kworker/2:2/2608 is trying to acquire lock: (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c9ddc>] drm_modeset_lock+0x7c/0x120 [drm] but task is already holding lock: (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm] other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(crtc_ww_class_mutex); lock(crtc_ww_class_mutex); *** DEADLOCK *** May be due to missing lock nesting notation 4 locks held by kworker/2:2/2608: #0: ("events"){.+.+.+}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0 #1: ((&arg.work)){+.+.+.}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0 #2: (crtc_ww_class_acquire){+.+.+.}, at: [<ffffffffc004532a>] drm_atomic_helper_remove_fb+0x4a/0x1d0 [drm_kms_helper] #3: (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm] While lockdep probably catches this bug when it happens, it's better to explicitly warn when state->acquire_ctx is not set. Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> --- drivers/gpu/drm/drm_atomic.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index 0b526423f19f..69adcf3944cc 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -263,6 +263,8 @@ drm_atomic_get_crtc_state(struct drm_atomic_state *state, int ret, index = drm_crtc_index(crtc); struct drm_crtc_state *crtc_state; + WARN_ON(!state->acquire_ctx); + crtc_state = drm_atomic_get_existing_crtc_state(state, crtc); if (crtc_state) return crtc_state; @@ -622,6 +624,8 @@ drm_atomic_get_plane_state(struct drm_atomic_state *state, int ret, index = drm_plane_index(plane); struct drm_plane_state *plane_state; + WARN_ON(!state->acquire_ctx); + plane_state = drm_atomic_get_existing_plane_state(state, plane); if (plane_state) return plane_state; @@ -890,6 +894,8 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state, struct drm_mode_config *config = &connector->dev->mode_config; struct drm_connector_state *connector_state; + WARN_ON(!state->acquire_ctx); + ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx); if (ret) return ERR_PTR(ret);