| Message ID | 20210826020122.1488002-8-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm: update locking for modesetting | expand |
On Thu, Aug 26, 2021 at 10:01:22AM +0800, Desmond Cheong Zhi Xi wrote: > Previously, master_lookup_lock was introduced in > commit 0b0860a3cf5e ("drm: serialize drm_file.master with a new > spinlock") to serialize accesses to drm_file.master. This then allowed > us to write drm_file_get_master in commit 56f0729a510f ("drm: protect > drm_master pointers in drm_lease.c"). > > The rationale behind introducing a new spinlock at the time was that > the other lock that could have been used (drm_device.master_mutex) was > the outermost lock, so embedding calls to drm_file_get_master and > drm_is_current_master in various functions easily caused us to invert > the lock hierarchy. > > Following the conversion of master_mutex into a rwsem, and its use to > plug races with modesetting rights, we've untangled some lock > hierarchies and removed the need for using drm_file_get_master and the > unlocked version of drm_is_current_master in multiple places. > > Hence, we can take this opportunity to clean up the locking design by > replacing master_lookup_lock with drm_device.master_rwsem. > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > --- > drivers/gpu/drm/drm_auth.c | 19 +++++++------------ > drivers/gpu/drm/drm_file.c | 1 - > drivers/gpu/drm/drm_internal.h | 1 + > drivers/gpu/drm/drm_ioctl.c | 4 ++-- > drivers/gpu/drm/drm_lease.c | 18 ++++++++---------- > include/drm/drm_file.h | 9 +-------- > 6 files changed, 19 insertions(+), 33 deletions(-) > > diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c > index f2b2f197052a..232416119407 100644 > --- a/drivers/gpu/drm/drm_auth.c > +++ b/drivers/gpu/drm/drm_auth.c > @@ -61,10 +61,9 @@ > * trusted clients. > */ > > -static bool drm_is_current_master_locked(struct drm_file *fpriv) > +bool drm_is_current_master_locked(struct drm_file *fpriv) > { > - lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) || > - lockdep_is_held(&fpriv->minor->dev->master_rwsem)); > + lockdep_assert_held_once(&fpriv->minor->dev->master_rwsem); > > return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; > } > @@ -83,9 +82,9 @@ bool drm_is_current_master(struct drm_file *fpriv) > { > bool ret; > > - spin_lock(&fpriv->master_lookup_lock); > + down_read(&fpriv->minor->dev->master_rwsem); Looking at the 3 patches and the need to have a locked version of pretty much everything I'm wondering: Can't we just drop the spinlock completely, and everywhere we've taking it thus far replace it with a lockdep_assert_held_once? The thing is, if there's any path left that doesn't hold the rwsem in at least read mode we have a bug. And the right way to fix such a bug is to grab the rwsem sufficiently high up in the callchain. That way I think we should be able to avoid all these tedious changes to everything, including touching i915 and vmwgfx drivers. Or am I missing something big time? -Daniel > ret = drm_is_current_master_locked(fpriv); > - spin_unlock(&fpriv->master_lookup_lock); > + up_read(&fpriv->minor->dev->master_rwsem); > > return ret; > } > @@ -120,7 +119,7 @@ int drm_authmagic(struct drm_device *dev, void *data, > DRM_DEBUG("%u\n", auth->magic); > > down_write(&dev->master_rwsem); > - if (unlikely(!drm_is_current_master(file_priv))) { > + if (unlikely(!drm_is_current_master_locked(file_priv))) { > up_write(&dev->master_rwsem); > return -EACCES; > } > @@ -178,9 +177,7 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) > new_master = drm_master_create(dev); > if (!new_master) > return -ENOMEM; > - spin_lock(&fpriv->master_lookup_lock); > fpriv->master = new_master; > - spin_unlock(&fpriv->master_lookup_lock); > > fpriv->is_master = 1; > fpriv->authenticated = 1; > @@ -343,9 +340,7 @@ int drm_master_open(struct drm_file *file_priv) > if (!dev->master) { > ret = drm_new_set_master(dev, file_priv); > } else { > - spin_lock(&file_priv->master_lookup_lock); > file_priv->master = drm_master_get(dev->master); > - spin_unlock(&file_priv->master_lookup_lock); > } > up_write(&dev->master_rwsem); > > @@ -413,13 +408,13 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv) > if (!file_priv) > return NULL; > > - spin_lock(&file_priv->master_lookup_lock); > + down_read(&file_priv->minor->dev->master_rwsem); > if (!file_priv->master) > goto unlock; > master = drm_master_get(file_priv->master); > > unlock: > - spin_unlock(&file_priv->master_lookup_lock); > + up_read(&file_priv->minor->dev->master_rwsem); > return master; > } > EXPORT_SYMBOL(drm_file_get_master); > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > index 90b62f360da1..8c846e0179d7 100644 > --- a/drivers/gpu/drm/drm_file.c > +++ b/drivers/gpu/drm/drm_file.c > @@ -176,7 +176,6 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) > init_waitqueue_head(&file->event_wait); > file->event_space = 4096; /* set aside 4k for event buffer */ > > - spin_lock_init(&file->master_lookup_lock); > mutex_init(&file->event_read_lock); > > if (drm_core_check_feature(dev, DRIVER_GEM)) > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h > index 17f3548c8ed2..5d421f749a17 100644 > --- a/drivers/gpu/drm/drm_internal.h > +++ b/drivers/gpu/drm/drm_internal.h > @@ -132,6 +132,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data, > struct drm_file *filp); > > /* drm_auth.c */ > +bool drm_is_current_master_locked(struct drm_file *fpriv); > int drm_getmagic(struct drm_device *dev, void *data, > struct drm_file *file_priv); > int drm_authmagic(struct drm_device *dev, void *data, > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c > index 8bea39ffc5c0..c728437466c3 100644 > --- a/drivers/gpu/drm/drm_ioctl.c > +++ b/drivers/gpu/drm/drm_ioctl.c > @@ -386,7 +386,7 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f > int if_version, retcode = 0; > > down_write(&dev->master_rwsem); > - if (unlikely(!drm_is_current_master(file_priv))) { > + if (unlikely(!drm_is_current_master_locked(file_priv))) { > retcode = -EACCES; > goto unlock; > } > @@ -540,7 +540,7 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv) > > /* MASTER is only for master or control clients */ > if (unlikely((flags & DRM_MASTER) && > - !drm_is_current_master(file_priv))) > + !drm_is_current_master_locked(file_priv))) > return -EACCES; > > /* Render clients must be explicitly allowed */ > diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c > index 15bf3a3c76d1..0eecf320b1ab 100644 > --- a/drivers/gpu/drm/drm_lease.c > +++ b/drivers/gpu/drm/drm_lease.c > @@ -498,12 +498,12 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, > return PTR_ERR(lessee_file); > > down_read(&dev->master_rwsem); > - if (unlikely(!drm_is_current_master(lessor_priv))) { > + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { > ret = -EACCES; > goto out_file; > } > > - lessor = drm_file_get_master(lessor_priv); > + lessor = lessor_priv->master; > /* Do not allow sub-leases */ > if (lessor->lessor) { > DRM_DEBUG_LEASE("recursive leasing not allowed\n"); > @@ -565,7 +565,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, > /* Hook up the fd */ > fd_install(fd, lessee_file); > > - drm_master_put(&lessor); > up_read(&dev->master_rwsem); > DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); > return 0; > @@ -600,7 +599,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, > if (!drm_core_check_feature(dev, DRIVER_MODESET)) > return -EOPNOTSUPP; > > - lessor = drm_file_get_master(lessor_priv); > + lockdep_assert_held_once(&dev->master_rwsem); > + lessor = lessor_priv->master; > DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id); > > mutex_lock(&dev->mode_config.idr_mutex); > @@ -624,7 +624,6 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, > arg->count_lessees = count; > > mutex_unlock(&dev->mode_config.idr_mutex); > - drm_master_put(&lessor); > > return ret; > } > @@ -650,7 +649,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, > if (!drm_core_check_feature(dev, DRIVER_MODESET)) > return -EOPNOTSUPP; > > - lessee = drm_file_get_master(lessee_priv); > + lockdep_assert_held_once(&dev->master_rwsem); > + lessee = lessee_priv->master; > DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id); > > mutex_lock(&dev->mode_config.idr_mutex); > @@ -678,7 +678,6 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, > arg->count_objects = count; > > mutex_unlock(&dev->mode_config.idr_mutex); > - drm_master_put(&lessee); > > return ret; > } > @@ -703,11 +702,11 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, > return -EOPNOTSUPP; > > down_write(&dev->master_rwsem); > - if (unlikely(!drm_is_current_master(lessor_priv))) { > + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { > ret = -EACCES; > goto unlock; > } > - lessor = drm_file_get_master(lessor_priv); > + lessor = lessor_priv->master; > mutex_lock(&dev->mode_config.idr_mutex); > > lessee = _drm_find_lessee(lessor, arg->lessee_id); > @@ -728,7 +727,6 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, > > fail: > mutex_unlock(&dev->mode_config.idr_mutex); > - drm_master_put(&lessor); > > unlock: > up_write(&dev->master_rwsem); > diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h > index d12bb2ba7814..e2d49fe3e32d 100644 > --- a/include/drm/drm_file.h > +++ b/include/drm/drm_file.h > @@ -227,16 +227,12 @@ struct drm_file { > * @master: > * > * Master this node is currently associated with. Protected by struct > - * &drm_device.master_rwsem, and serialized by @master_lookup_lock. > + * &drm_device.master_rwsem. > * > * Only relevant if drm_is_primary_client() returns true. Note that > * this only matches &drm_device.master if the master is the currently > * active one. > * > - * To update @master, both &drm_device.master_rwsem and > - * @master_lookup_lock need to be held, therefore holding either of > - * them is safe and enough for the read side. > - * > * When dereferencing this pointer, either hold struct > * &drm_device.master_rwsem for the duration of the pointer's use, or > * use drm_file_get_master() if struct &drm_device.master_rwsem is not > @@ -248,9 +244,6 @@ struct drm_file { > */ > struct drm_master *master; > > - /** @master_lock: Serializes @master. */ > - spinlock_t master_lookup_lock; > - > /** @pid: Process that opened this file. */ > struct pid *pid; > > -- > 2.25.1 >
On 26/8/21 9:21 pm, Daniel Vetter wrote: > On Thu, Aug 26, 2021 at 10:01:22AM +0800, Desmond Cheong Zhi Xi wrote: >> Previously, master_lookup_lock was introduced in >> commit 0b0860a3cf5e ("drm: serialize drm_file.master with a new >> spinlock") to serialize accesses to drm_file.master. This then allowed >> us to write drm_file_get_master in commit 56f0729a510f ("drm: protect >> drm_master pointers in drm_lease.c"). >> >> The rationale behind introducing a new spinlock at the time was that >> the other lock that could have been used (drm_device.master_mutex) was >> the outermost lock, so embedding calls to drm_file_get_master and >> drm_is_current_master in various functions easily caused us to invert >> the lock hierarchy. >> >> Following the conversion of master_mutex into a rwsem, and its use to >> plug races with modesetting rights, we've untangled some lock >> hierarchies and removed the need for using drm_file_get_master and the >> unlocked version of drm_is_current_master in multiple places. >> >> Hence, we can take this opportunity to clean up the locking design by >> replacing master_lookup_lock with drm_device.master_rwsem. >> >> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> >> --- >> drivers/gpu/drm/drm_auth.c | 19 +++++++------------ >> drivers/gpu/drm/drm_file.c | 1 - >> drivers/gpu/drm/drm_internal.h | 1 + >> drivers/gpu/drm/drm_ioctl.c | 4 ++-- >> drivers/gpu/drm/drm_lease.c | 18 ++++++++---------- >> include/drm/drm_file.h | 9 +-------- >> 6 files changed, 19 insertions(+), 33 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c >> index f2b2f197052a..232416119407 100644 >> --- a/drivers/gpu/drm/drm_auth.c >> +++ b/drivers/gpu/drm/drm_auth.c >> @@ -61,10 +61,9 @@ >> * trusted clients. >> */ >> >> -static bool drm_is_current_master_locked(struct drm_file *fpriv) >> +bool drm_is_current_master_locked(struct drm_file *fpriv) >> { >> - lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) || >> - lockdep_is_held(&fpriv->minor->dev->master_rwsem)); >> + lockdep_assert_held_once(&fpriv->minor->dev->master_rwsem); >> >> return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; >> } >> @@ -83,9 +82,9 @@ bool drm_is_current_master(struct drm_file *fpriv) >> { >> bool ret; >> >> - spin_lock(&fpriv->master_lookup_lock); >> + down_read(&fpriv->minor->dev->master_rwsem); > > Looking at the 3 patches and the need to have a locked version of pretty > much everything I'm wondering: Can't we just drop the spinlock completely, > and everywhere we've taking it thus far replace it with a > lockdep_assert_held_once? > > The thing is, if there's any path left that doesn't hold the rwsem in at > least read mode we have a bug. And the right way to fix such a bug is to > grab the rwsem sufficiently high up in the callchain. That way I think we > should be able to avoid all these tedious changes to everything, including > touching i915 and vmwgfx drivers. > > Or am I missing something big time? > -Daniel > Thanks for taking a look at all the patches and for the suggestions, Daniel. Just my two cents. I think it makes sense to replace the lock with the lockdep assertion. This avoids the weirdness with the lock being taken both as an outer lock and sometimes as a deeply embedded inner lock. But we'll probably have to fix some stuff because I don't think we always hold the rwsem in the places where the spinlock is grabbed (i.e. when drm_is_current_master or drm_file_get_master is called). I'll split the series as suggested so we can test things up to PATCH 4 ("drm: avoid races with modesetting rights"). For the rest of the series to remove the spinlock, I'll take a closer look and probably send out a patch later this week. Best wishes, Desmond >> ret = drm_is_current_master_locked(fpriv); >> - spin_unlock(&fpriv->master_lookup_lock); >> + up_read(&fpriv->minor->dev->master_rwsem); >> >> return ret; >> } >> @@ -120,7 +119,7 @@ int drm_authmagic(struct drm_device *dev, void *data, >> DRM_DEBUG("%u\n", auth->magic); >> >> down_write(&dev->master_rwsem); >> - if (unlikely(!drm_is_current_master(file_priv))) { >> + if (unlikely(!drm_is_current_master_locked(file_priv))) { >> up_write(&dev->master_rwsem); >> return -EACCES; >> } >> @@ -178,9 +177,7 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) >> new_master = drm_master_create(dev); >> if (!new_master) >> return -ENOMEM; >> - spin_lock(&fpriv->master_lookup_lock); >> fpriv->master = new_master; >> - spin_unlock(&fpriv->master_lookup_lock); >> >> fpriv->is_master = 1; >> fpriv->authenticated = 1; >> @@ -343,9 +340,7 @@ int drm_master_open(struct drm_file *file_priv) >> if (!dev->master) { >> ret = drm_new_set_master(dev, file_priv); >> } else { >> - spin_lock(&file_priv->master_lookup_lock); >> file_priv->master = drm_master_get(dev->master); >> - spin_unlock(&file_priv->master_lookup_lock); >> } >> up_write(&dev->master_rwsem); >> >> @@ -413,13 +408,13 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv) >> if (!file_priv) >> return NULL; >> >> - spin_lock(&file_priv->master_lookup_lock); >> + down_read(&file_priv->minor->dev->master_rwsem); >> if (!file_priv->master) >> goto unlock; >> master = drm_master_get(file_priv->master); >> >> unlock: >> - spin_unlock(&file_priv->master_lookup_lock); >> + up_read(&file_priv->minor->dev->master_rwsem); >> return master; >> } >> EXPORT_SYMBOL(drm_file_get_master); >> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c >> index 90b62f360da1..8c846e0179d7 100644 >> --- a/drivers/gpu/drm/drm_file.c >> +++ b/drivers/gpu/drm/drm_file.c >> @@ -176,7 +176,6 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) >> init_waitqueue_head(&file->event_wait); >> file->event_space = 4096; /* set aside 4k for event buffer */ >> >> - spin_lock_init(&file->master_lookup_lock); >> mutex_init(&file->event_read_lock); >> >> if (drm_core_check_feature(dev, DRIVER_GEM)) >> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h >> index 17f3548c8ed2..5d421f749a17 100644 >> --- a/drivers/gpu/drm/drm_internal.h >> +++ b/drivers/gpu/drm/drm_internal.h >> @@ -132,6 +132,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data, >> struct drm_file *filp); >> >> /* drm_auth.c */ >> +bool drm_is_current_master_locked(struct drm_file *fpriv); >> int drm_getmagic(struct drm_device *dev, void *data, >> struct drm_file *file_priv); >> int drm_authmagic(struct drm_device *dev, void *data, >> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c >> index 8bea39ffc5c0..c728437466c3 100644 >> --- a/drivers/gpu/drm/drm_ioctl.c >> +++ b/drivers/gpu/drm/drm_ioctl.c >> @@ -386,7 +386,7 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f >> int if_version, retcode = 0; >> >> down_write(&dev->master_rwsem); >> - if (unlikely(!drm_is_current_master(file_priv))) { >> + if (unlikely(!drm_is_current_master_locked(file_priv))) { >> retcode = -EACCES; >> goto unlock; >> } >> @@ -540,7 +540,7 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv) >> >> /* MASTER is only for master or control clients */ >> if (unlikely((flags & DRM_MASTER) && >> - !drm_is_current_master(file_priv))) >> + !drm_is_current_master_locked(file_priv))) >> return -EACCES; >> >> /* Render clients must be explicitly allowed */ >> diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c >> index 15bf3a3c76d1..0eecf320b1ab 100644 >> --- a/drivers/gpu/drm/drm_lease.c >> +++ b/drivers/gpu/drm/drm_lease.c >> @@ -498,12 +498,12 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, >> return PTR_ERR(lessee_file); >> >> down_read(&dev->master_rwsem); >> - if (unlikely(!drm_is_current_master(lessor_priv))) { >> + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { >> ret = -EACCES; >> goto out_file; >> } >> >> - lessor = drm_file_get_master(lessor_priv); >> + lessor = lessor_priv->master; >> /* Do not allow sub-leases */ >> if (lessor->lessor) { >> DRM_DEBUG_LEASE("recursive leasing not allowed\n"); >> @@ -565,7 +565,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, >> /* Hook up the fd */ >> fd_install(fd, lessee_file); >> >> - drm_master_put(&lessor); >> up_read(&dev->master_rwsem); >> DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); >> return 0; >> @@ -600,7 +599,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, >> if (!drm_core_check_feature(dev, DRIVER_MODESET)) >> return -EOPNOTSUPP; >> >> - lessor = drm_file_get_master(lessor_priv); >> + lockdep_assert_held_once(&dev->master_rwsem); >> + lessor = lessor_priv->master; >> DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id); >> >> mutex_lock(&dev->mode_config.idr_mutex); >> @@ -624,7 +624,6 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, >> arg->count_lessees = count; >> >> mutex_unlock(&dev->mode_config.idr_mutex); >> - drm_master_put(&lessor); >> >> return ret; >> } >> @@ -650,7 +649,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, >> if (!drm_core_check_feature(dev, DRIVER_MODESET)) >> return -EOPNOTSUPP; >> >> - lessee = drm_file_get_master(lessee_priv); >> + lockdep_assert_held_once(&dev->master_rwsem); >> + lessee = lessee_priv->master; >> DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id); >> >> mutex_lock(&dev->mode_config.idr_mutex); >> @@ -678,7 +678,6 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, >> arg->count_objects = count; >> >> mutex_unlock(&dev->mode_config.idr_mutex); >> - drm_master_put(&lessee); >> >> return ret; >> } >> @@ -703,11 +702,11 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, >> return -EOPNOTSUPP; >> >> down_write(&dev->master_rwsem); >> - if (unlikely(!drm_is_current_master(lessor_priv))) { >> + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { >> ret = -EACCES; >> goto unlock; >> } >> - lessor = drm_file_get_master(lessor_priv); >> + lessor = lessor_priv->master; >> mutex_lock(&dev->mode_config.idr_mutex); >> >> lessee = _drm_find_lessee(lessor, arg->lessee_id); >> @@ -728,7 +727,6 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, >> >> fail: >> mutex_unlock(&dev->mode_config.idr_mutex); >> - drm_master_put(&lessor); >> >> unlock: >> up_write(&dev->master_rwsem); >> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h >> index d12bb2ba7814..e2d49fe3e32d 100644 >> --- a/include/drm/drm_file.h >> +++ b/include/drm/drm_file.h >> @@ -227,16 +227,12 @@ struct drm_file { >> * @master: >> * >> * Master this node is currently associated with. Protected by struct >> - * &drm_device.master_rwsem, and serialized by @master_lookup_lock. >> + * &drm_device.master_rwsem. >> * >> * Only relevant if drm_is_primary_client() returns true. Note that >> * this only matches &drm_device.master if the master is the currently >> * active one. >> * >> - * To update @master, both &drm_device.master_rwsem and >> - * @master_lookup_lock need to be held, therefore holding either of >> - * them is safe and enough for the read side. >> - * >> * When dereferencing this pointer, either hold struct >> * &drm_device.master_rwsem for the duration of the pointer's use, or >> * use drm_file_get_master() if struct &drm_device.master_rwsem is not >> @@ -248,9 +244,6 @@ struct drm_file { >> */ >> struct drm_master *master; >> >> - /** @master_lock: Serializes @master. */ >> - spinlock_t master_lookup_lock; >> - >> /** @pid: Process that opened this file. */ >> struct pid *pid; >> >> -- >> 2.25.1 >> >
On Tue, Aug 31, 2021 at 02:02:39PM +0800, Desmond Cheong Zhi Xi wrote: > On 26/8/21 9:21 pm, Daniel Vetter wrote: > > On Thu, Aug 26, 2021 at 10:01:22AM +0800, Desmond Cheong Zhi Xi wrote: > > > Previously, master_lookup_lock was introduced in > > > commit 0b0860a3cf5e ("drm: serialize drm_file.master with a new > > > spinlock") to serialize accesses to drm_file.master. This then allowed > > > us to write drm_file_get_master in commit 56f0729a510f ("drm: protect > > > drm_master pointers in drm_lease.c"). > > > > > > The rationale behind introducing a new spinlock at the time was that > > > the other lock that could have been used (drm_device.master_mutex) was > > > the outermost lock, so embedding calls to drm_file_get_master and > > > drm_is_current_master in various functions easily caused us to invert > > > the lock hierarchy. > > > > > > Following the conversion of master_mutex into a rwsem, and its use to > > > plug races with modesetting rights, we've untangled some lock > > > hierarchies and removed the need for using drm_file_get_master and the > > > unlocked version of drm_is_current_master in multiple places. > > > > > > Hence, we can take this opportunity to clean up the locking design by > > > replacing master_lookup_lock with drm_device.master_rwsem. > > > > > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > > > --- > > > drivers/gpu/drm/drm_auth.c | 19 +++++++------------ > > > drivers/gpu/drm/drm_file.c | 1 - > > > drivers/gpu/drm/drm_internal.h | 1 + > > > drivers/gpu/drm/drm_ioctl.c | 4 ++-- > > > drivers/gpu/drm/drm_lease.c | 18 ++++++++---------- > > > include/drm/drm_file.h | 9 +-------- > > > 6 files changed, 19 insertions(+), 33 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c > > > index f2b2f197052a..232416119407 100644 > > > --- a/drivers/gpu/drm/drm_auth.c > > > +++ b/drivers/gpu/drm/drm_auth.c > > > @@ -61,10 +61,9 @@ > > > * trusted clients. > > > */ > > > -static bool drm_is_current_master_locked(struct drm_file *fpriv) > > > +bool drm_is_current_master_locked(struct drm_file *fpriv) > > > { > > > - lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) || > > > - lockdep_is_held(&fpriv->minor->dev->master_rwsem)); > > > + lockdep_assert_held_once(&fpriv->minor->dev->master_rwsem); > > > return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; > > > } > > > @@ -83,9 +82,9 @@ bool drm_is_current_master(struct drm_file *fpriv) > > > { > > > bool ret; > > > - spin_lock(&fpriv->master_lookup_lock); > > > + down_read(&fpriv->minor->dev->master_rwsem); > > > > Looking at the 3 patches and the need to have a locked version of pretty > > much everything I'm wondering: Can't we just drop the spinlock completely, > > and everywhere we've taking it thus far replace it with a > > lockdep_assert_held_once? > > > > The thing is, if there's any path left that doesn't hold the rwsem in at > > least read mode we have a bug. And the right way to fix such a bug is to > > grab the rwsem sufficiently high up in the callchain. That way I think we > > should be able to avoid all these tedious changes to everything, including > > touching i915 and vmwgfx drivers. > > > > Or am I missing something big time? > > -Daniel > > > > Thanks for taking a look at all the patches and for the suggestions, Daniel. > > Just my two cents. I think it makes sense to replace the lock with the > lockdep assertion. This avoids the weirdness with the lock being taken both > as an outer lock and sometimes as a deeply embedded inner lock. > > But we'll probably have to fix some stuff because I don't think we always > hold the rwsem in the places where the spinlock is grabbed (i.e. when > drm_is_current_master or drm_file_get_master is called). Yeah right I forgot about that again when coming up with this idea. All the ioctl that read kms state need a read lock too. Maybe those ioctl could just grab the master rwsem themselves? This should work now that we've untangled the drm_global_mutex situation I think. > I'll split the series as suggested so we can test things up to PATCH 4 > ("drm: avoid races with modesetting rights"). For the rest of the series to > remove the spinlock, I'll take a closer look and probably send out a patch > later this week. Sounds great! -Daniel > > Best wishes, > Desmond > > > > ret = drm_is_current_master_locked(fpriv); > > > - spin_unlock(&fpriv->master_lookup_lock); > > > + up_read(&fpriv->minor->dev->master_rwsem); > > > return ret; > > > } > > > @@ -120,7 +119,7 @@ int drm_authmagic(struct drm_device *dev, void *data, > > > DRM_DEBUG("%u\n", auth->magic); > > > down_write(&dev->master_rwsem); > > > - if (unlikely(!drm_is_current_master(file_priv))) { > > > + if (unlikely(!drm_is_current_master_locked(file_priv))) { > > > up_write(&dev->master_rwsem); > > > return -EACCES; > > > } > > > @@ -178,9 +177,7 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) > > > new_master = drm_master_create(dev); > > > if (!new_master) > > > return -ENOMEM; > > > - spin_lock(&fpriv->master_lookup_lock); > > > fpriv->master = new_master; > > > - spin_unlock(&fpriv->master_lookup_lock); > > > fpriv->is_master = 1; > > > fpriv->authenticated = 1; > > > @@ -343,9 +340,7 @@ int drm_master_open(struct drm_file *file_priv) > > > if (!dev->master) { > > > ret = drm_new_set_master(dev, file_priv); > > > } else { > > > - spin_lock(&file_priv->master_lookup_lock); > > > file_priv->master = drm_master_get(dev->master); > > > - spin_unlock(&file_priv->master_lookup_lock); > > > } > > > up_write(&dev->master_rwsem); > > > @@ -413,13 +408,13 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv) > > > if (!file_priv) > > > return NULL; > > > - spin_lock(&file_priv->master_lookup_lock); > > > + down_read(&file_priv->minor->dev->master_rwsem); > > > if (!file_priv->master) > > > goto unlock; > > > master = drm_master_get(file_priv->master); > > > unlock: > > > - spin_unlock(&file_priv->master_lookup_lock); > > > + up_read(&file_priv->minor->dev->master_rwsem); > > > return master; > > > } > > > EXPORT_SYMBOL(drm_file_get_master); > > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > > > index 90b62f360da1..8c846e0179d7 100644 > > > --- a/drivers/gpu/drm/drm_file.c > > > +++ b/drivers/gpu/drm/drm_file.c > > > @@ -176,7 +176,6 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) > > > init_waitqueue_head(&file->event_wait); > > > file->event_space = 4096; /* set aside 4k for event buffer */ > > > - spin_lock_init(&file->master_lookup_lock); > > > mutex_init(&file->event_read_lock); > > > if (drm_core_check_feature(dev, DRIVER_GEM)) > > > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h > > > index 17f3548c8ed2..5d421f749a17 100644 > > > --- a/drivers/gpu/drm/drm_internal.h > > > +++ b/drivers/gpu/drm/drm_internal.h > > > @@ -132,6 +132,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data, > > > struct drm_file *filp); > > > /* drm_auth.c */ > > > +bool drm_is_current_master_locked(struct drm_file *fpriv); > > > int drm_getmagic(struct drm_device *dev, void *data, > > > struct drm_file *file_priv); > > > int drm_authmagic(struct drm_device *dev, void *data, > > > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c > > > index 8bea39ffc5c0..c728437466c3 100644 > > > --- a/drivers/gpu/drm/drm_ioctl.c > > > +++ b/drivers/gpu/drm/drm_ioctl.c > > > @@ -386,7 +386,7 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f > > > int if_version, retcode = 0; > > > down_write(&dev->master_rwsem); > > > - if (unlikely(!drm_is_current_master(file_priv))) { > > > + if (unlikely(!drm_is_current_master_locked(file_priv))) { > > > retcode = -EACCES; > > > goto unlock; > > > } > > > @@ -540,7 +540,7 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv) > > > /* MASTER is only for master or control clients */ > > > if (unlikely((flags & DRM_MASTER) && > > > - !drm_is_current_master(file_priv))) > > > + !drm_is_current_master_locked(file_priv))) > > > return -EACCES; > > > /* Render clients must be explicitly allowed */ > > > diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c > > > index 15bf3a3c76d1..0eecf320b1ab 100644 > > > --- a/drivers/gpu/drm/drm_lease.c > > > +++ b/drivers/gpu/drm/drm_lease.c > > > @@ -498,12 +498,12 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, > > > return PTR_ERR(lessee_file); > > > down_read(&dev->master_rwsem); > > > - if (unlikely(!drm_is_current_master(lessor_priv))) { > > > + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { > > > ret = -EACCES; > > > goto out_file; > > > } > > > - lessor = drm_file_get_master(lessor_priv); > > > + lessor = lessor_priv->master; > > > /* Do not allow sub-leases */ > > > if (lessor->lessor) { > > > DRM_DEBUG_LEASE("recursive leasing not allowed\n"); > > > @@ -565,7 +565,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, > > > /* Hook up the fd */ > > > fd_install(fd, lessee_file); > > > - drm_master_put(&lessor); > > > up_read(&dev->master_rwsem); > > > DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); > > > return 0; > > > @@ -600,7 +599,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, > > > if (!drm_core_check_feature(dev, DRIVER_MODESET)) > > > return -EOPNOTSUPP; > > > - lessor = drm_file_get_master(lessor_priv); > > > + lockdep_assert_held_once(&dev->master_rwsem); > > > + lessor = lessor_priv->master; > > > DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id); > > > mutex_lock(&dev->mode_config.idr_mutex); > > > @@ -624,7 +624,6 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, > > > arg->count_lessees = count; > > > mutex_unlock(&dev->mode_config.idr_mutex); > > > - drm_master_put(&lessor); > > > return ret; > > > } > > > @@ -650,7 +649,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, > > > if (!drm_core_check_feature(dev, DRIVER_MODESET)) > > > return -EOPNOTSUPP; > > > - lessee = drm_file_get_master(lessee_priv); > > > + lockdep_assert_held_once(&dev->master_rwsem); > > > + lessee = lessee_priv->master; > > > DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id); > > > mutex_lock(&dev->mode_config.idr_mutex); > > > @@ -678,7 +678,6 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, > > > arg->count_objects = count; > > > mutex_unlock(&dev->mode_config.idr_mutex); > > > - drm_master_put(&lessee); > > > return ret; > > > } > > > @@ -703,11 +702,11 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, > > > return -EOPNOTSUPP; > > > down_write(&dev->master_rwsem); > > > - if (unlikely(!drm_is_current_master(lessor_priv))) { > > > + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { > > > ret = -EACCES; > > > goto unlock; > > > } > > > - lessor = drm_file_get_master(lessor_priv); > > > + lessor = lessor_priv->master; > > > mutex_lock(&dev->mode_config.idr_mutex); > > > lessee = _drm_find_lessee(lessor, arg->lessee_id); > > > @@ -728,7 +727,6 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, > > > fail: > > > mutex_unlock(&dev->mode_config.idr_mutex); > > > - drm_master_put(&lessor); > > > unlock: > > > up_write(&dev->master_rwsem); > > > diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h > > > index d12bb2ba7814..e2d49fe3e32d 100644 > > > --- a/include/drm/drm_file.h > > > +++ b/include/drm/drm_file.h > > > @@ -227,16 +227,12 @@ struct drm_file { > > > * @master: > > > * > > > * Master this node is currently associated with. Protected by struct > > > - * &drm_device.master_rwsem, and serialized by @master_lookup_lock. > > > + * &drm_device.master_rwsem. > > > * > > > * Only relevant if drm_is_primary_client() returns true. Note that > > > * this only matches &drm_device.master if the master is the currently > > > * active one. > > > * > > > - * To update @master, both &drm_device.master_rwsem and > > > - * @master_lookup_lock need to be held, therefore holding either of > > > - * them is safe and enough for the read side. > > > - * > > > * When dereferencing this pointer, either hold struct > > > * &drm_device.master_rwsem for the duration of the pointer's use, or > > > * use drm_file_get_master() if struct &drm_device.master_rwsem is not > > > @@ -248,9 +244,6 @@ struct drm_file { > > > */ > > > struct drm_master *master; > > > - /** @master_lock: Serializes @master. */ > > > - spinlock_t master_lookup_lock; > > > - > > > /** @pid: Process that opened this file. */ > > > struct pid *pid; > > > -- > > > 2.25.1 > > > > > >
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index f2b2f197052a..232416119407 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -61,10 +61,9 @@ * trusted clients. */ -static bool drm_is_current_master_locked(struct drm_file *fpriv) +bool drm_is_current_master_locked(struct drm_file *fpriv) { - lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) || - lockdep_is_held(&fpriv->minor->dev->master_rwsem)); + lockdep_assert_held_once(&fpriv->minor->dev->master_rwsem); return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; } @@ -83,9 +82,9 @@ bool drm_is_current_master(struct drm_file *fpriv) { bool ret; - spin_lock(&fpriv->master_lookup_lock); + down_read(&fpriv->minor->dev->master_rwsem); ret = drm_is_current_master_locked(fpriv); - spin_unlock(&fpriv->master_lookup_lock); + up_read(&fpriv->minor->dev->master_rwsem); return ret; } @@ -120,7 +119,7 @@ int drm_authmagic(struct drm_device *dev, void *data, DRM_DEBUG("%u\n", auth->magic); down_write(&dev->master_rwsem); - if (unlikely(!drm_is_current_master(file_priv))) { + if (unlikely(!drm_is_current_master_locked(file_priv))) { up_write(&dev->master_rwsem); return -EACCES; } @@ -178,9 +177,7 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) new_master = drm_master_create(dev); if (!new_master) return -ENOMEM; - spin_lock(&fpriv->master_lookup_lock); fpriv->master = new_master; - spin_unlock(&fpriv->master_lookup_lock); fpriv->is_master = 1; fpriv->authenticated = 1; @@ -343,9 +340,7 @@ int drm_master_open(struct drm_file *file_priv) if (!dev->master) { ret = drm_new_set_master(dev, file_priv); } else { - spin_lock(&file_priv->master_lookup_lock); file_priv->master = drm_master_get(dev->master); - spin_unlock(&file_priv->master_lookup_lock); } up_write(&dev->master_rwsem); @@ -413,13 +408,13 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv) if (!file_priv) return NULL; - spin_lock(&file_priv->master_lookup_lock); + down_read(&file_priv->minor->dev->master_rwsem); if (!file_priv->master) goto unlock; master = drm_master_get(file_priv->master); unlock: - spin_unlock(&file_priv->master_lookup_lock); + up_read(&file_priv->minor->dev->master_rwsem); return master; } EXPORT_SYMBOL(drm_file_get_master); diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c index 90b62f360da1..8c846e0179d7 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -176,7 +176,6 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) init_waitqueue_head(&file->event_wait); file->event_space = 4096; /* set aside 4k for event buffer */ - spin_lock_init(&file->master_lookup_lock); mutex_init(&file->event_read_lock); if (drm_core_check_feature(dev, DRIVER_GEM)) diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h index 17f3548c8ed2..5d421f749a17 100644 --- a/drivers/gpu/drm/drm_internal.h +++ b/drivers/gpu/drm/drm_internal.h @@ -132,6 +132,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data, struct drm_file *filp); /* drm_auth.c */ +bool drm_is_current_master_locked(struct drm_file *fpriv); int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv); int drm_authmagic(struct drm_device *dev, void *data, diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index 8bea39ffc5c0..c728437466c3 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -386,7 +386,7 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f int if_version, retcode = 0; down_write(&dev->master_rwsem); - if (unlikely(!drm_is_current_master(file_priv))) { + if (unlikely(!drm_is_current_master_locked(file_priv))) { retcode = -EACCES; goto unlock; } @@ -540,7 +540,7 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv) /* MASTER is only for master or control clients */ if (unlikely((flags & DRM_MASTER) && - !drm_is_current_master(file_priv))) + !drm_is_current_master_locked(file_priv))) return -EACCES; /* Render clients must be explicitly allowed */ diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index 15bf3a3c76d1..0eecf320b1ab 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -498,12 +498,12 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, return PTR_ERR(lessee_file); down_read(&dev->master_rwsem); - if (unlikely(!drm_is_current_master(lessor_priv))) { + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { ret = -EACCES; goto out_file; } - lessor = drm_file_get_master(lessor_priv); + lessor = lessor_priv->master; /* Do not allow sub-leases */ if (lessor->lessor) { DRM_DEBUG_LEASE("recursive leasing not allowed\n"); @@ -565,7 +565,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, /* Hook up the fd */ fd_install(fd, lessee_file); - drm_master_put(&lessor); up_read(&dev->master_rwsem); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); return 0; @@ -600,7 +599,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP; - lessor = drm_file_get_master(lessor_priv); + lockdep_assert_held_once(&dev->master_rwsem); + lessor = lessor_priv->master; DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id); mutex_lock(&dev->mode_config.idr_mutex); @@ -624,7 +624,6 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, arg->count_lessees = count; mutex_unlock(&dev->mode_config.idr_mutex); - drm_master_put(&lessor); return ret; } @@ -650,7 +649,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP; - lessee = drm_file_get_master(lessee_priv); + lockdep_assert_held_once(&dev->master_rwsem); + lessee = lessee_priv->master; DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id); mutex_lock(&dev->mode_config.idr_mutex); @@ -678,7 +678,6 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, arg->count_objects = count; mutex_unlock(&dev->mode_config.idr_mutex); - drm_master_put(&lessee); return ret; } @@ -703,11 +702,11 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, return -EOPNOTSUPP; down_write(&dev->master_rwsem); - if (unlikely(!drm_is_current_master(lessor_priv))) { + if (unlikely(!drm_is_current_master_locked(lessor_priv))) { ret = -EACCES; goto unlock; } - lessor = drm_file_get_master(lessor_priv); + lessor = lessor_priv->master; mutex_lock(&dev->mode_config.idr_mutex); lessee = _drm_find_lessee(lessor, arg->lessee_id); @@ -728,7 +727,6 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, fail: mutex_unlock(&dev->mode_config.idr_mutex); - drm_master_put(&lessor); unlock: up_write(&dev->master_rwsem); diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h index d12bb2ba7814..e2d49fe3e32d 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -227,16 +227,12 @@ struct drm_file { * @master: * * Master this node is currently associated with. Protected by struct - * &drm_device.master_rwsem, and serialized by @master_lookup_lock. + * &drm_device.master_rwsem. * * Only relevant if drm_is_primary_client() returns true. Note that * this only matches &drm_device.master if the master is the currently * active one. * - * To update @master, both &drm_device.master_rwsem and - * @master_lookup_lock need to be held, therefore holding either of - * them is safe and enough for the read side. - * * When dereferencing this pointer, either hold struct * &drm_device.master_rwsem for the duration of the pointer's use, or * use drm_file_get_master() if struct &drm_device.master_rwsem is not @@ -248,9 +244,6 @@ struct drm_file { */ struct drm_master *master; - /** @master_lock: Serializes @master. */ - spinlock_t master_lookup_lock; - /** @pid: Process that opened this file. */ struct pid *pid;
Previously, master_lookup_lock was introduced in commit 0b0860a3cf5e ("drm: serialize drm_file.master with a new spinlock") to serialize accesses to drm_file.master. This then allowed us to write drm_file_get_master in commit 56f0729a510f ("drm: protect drm_master pointers in drm_lease.c"). The rationale behind introducing a new spinlock at the time was that the other lock that could have been used (drm_device.master_mutex) was the outermost lock, so embedding calls to drm_file_get_master and drm_is_current_master in various functions easily caused us to invert the lock hierarchy. Following the conversion of master_mutex into a rwsem, and its use to plug races with modesetting rights, we've untangled some lock hierarchies and removed the need for using drm_file_get_master and the unlocked version of drm_is_current_master in multiple places. Hence, we can take this opportunity to clean up the locking design by replacing master_lookup_lock with drm_device.master_rwsem. Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- drivers/gpu/drm/drm_auth.c | 19 +++++++------------ drivers/gpu/drm/drm_file.c | 1 - drivers/gpu/drm/drm_internal.h | 1 + drivers/gpu/drm/drm_ioctl.c | 4 ++-- drivers/gpu/drm/drm_lease.c | 18 ++++++++---------- include/drm/drm_file.h | 9 +-------- 6 files changed, 19 insertions(+), 33 deletions(-)