On Fri, Dec 5, 2025 at 4:43 AM Boris Brezillon <[email protected]> wrote: > > On Thu, 4 Dec 2025 09:45:45 -0800 > Chia-I Wu <[email protected]> wrote: > > > Commit 506aa8b02a8d6 ("dma-fence: Add safe access helpers and document > > the rules") details the dma-fence safe access rules. The most common > > culprit is that drm_sched_fence_get_timeline_name may race with > > group_free_queue. > > > > Signed-off-by: Chia-I Wu <[email protected]> > > Reviewed-by: Boris Brezillon <[email protected]> > > Reviewed-by: Liviu Dudau <[email protected]> > > Reviewed-by: Steven Price <[email protected]> > > > > --- > > v2: collect R-bs and drop misleading Fixes: tag > > Should we at least > > Cc: [email protected] > > so this gets considered for backporting? This can be considered a follow-up to commit 506aa8b02a8d6. I think
Cc: [email protected] # v6.17+ is appropriate. (Not sure if I should send v3 or leave it to maintainers, because I was once told to never add the line and always leave it to maintainers). To help make the decision, commit 506aa8b02a8d6 itself narrowed the race window greatly. This follow-up closes the remaining case where panthor signals the fence and destroys the group while the consumer holds the rcu read lock. > > > --- > > drivers/gpu/drm/panthor/panthor_sched.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c > > b/drivers/gpu/drm/panthor/panthor_sched.c > > index 33b9ef537e359..a8b1347e4da71 100644 > > --- a/drivers/gpu/drm/panthor/panthor_sched.c > > +++ b/drivers/gpu/drm/panthor/panthor_sched.c > > @@ -23,6 +23,7 @@ > > #include <linux/module.h> > > #include <linux/platform_device.h> > > #include <linux/pm_runtime.h> > > +#include <linux/rcupdate.h> > > > > #include "panthor_devfreq.h" > > #include "panthor_device.h" > > @@ -923,6 +924,9 @@ static void group_release_work(struct work_struct *work) > > release_work); > > u32 i; > > > > + /* dma-fences may still be accessing group->queues under rcu lock. */ > > + synchronize_rcu(); > > + > > for (i = 0; i < group->queue_count; i++) > > group_free_queue(group, group->queues[i]); > > >
