On 4/21/24 19:39, Adrián Larumbe wrote: > When Panfrost must pin an object that is being prepared a dma-buf > attachment for on behalf of another driver, the core drm gem object pinning > code already takes a lock on the object's dma reservation. > > However, Panfrost GEM object's pinning callback would eventually try taking > the lock on the same dma reservation when delegating pinning of the object > onto the shmem subsystem, which led to a deadlock. > > This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws > the following recursive locking situation: > > weston/3440 is trying to acquire lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_pin+0x34/0xb8 [drm_shmem_helper] > but task is already holding lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pin+0x2c/0x80 [drm] > > Fix it by assuming the object's reservation had already been locked by the > time we reach panfrost_gem_pin. > > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> > Cc: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> > Cc: Steven Price <steven.price@xxxxxxx> > Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()") > Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> > --- > drivers/gpu/drm/panfrost/panfrost_gem.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c > index d47b40b82b0b..6c26652d425d 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_gem.c > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c > @@ -192,7 +192,12 @@ static int panfrost_gem_pin(struct drm_gem_object *obj) > if (bo->is_heap) > return -EINVAL; > > - return drm_gem_shmem_pin(&bo->base); > + /* > + * Pinning can only happen in response to a prime attachment request from > + * another driver, but that's already being handled by drm_gem_pin > + */ > + drm_WARN_ON(obj->dev, obj->import_attach); > + return drm_gem_shmem_pin_locked(&bo->base); > } Will be better to use drm_gem_shmem_object_pin() to avoid such problem in future Please also fix the Lima driver -- Best regards, Dmitry