On 05/12/2025 18:45, Chia-I Wu wrote: > 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. >
I've pushed this to drm-misc-next with the Cc tag. Thanks, Steve >> >>> --- >>> 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]); >>> >>
