On 22/10/2025 13:37, Boris Brezillon wrote: > On Wed, 22 Oct 2025 12:30:13 +0200 > Ketil Johnsen <[email protected]> wrote: > >> The function panthor_fw_unplug() will free the FW memory sections. >> The problem is that there could still be pending FW events which are yet >> not handled at this point. process_fw_events_work() can in this case try >> to access said freed memory. >> >> This fix introduces a destroyed state for the panthor_scheduler object, >> and we check for this before processing FW events. >> >> Signed-off-by: Ketil Johnsen <[email protected]> >> Fixes: de85488138247 ("drm/panthor: Add the scheduler logical block") >> --- >> v2: >> - Followed Boris's advice and handle the race purely within the >> scheduler block (by adding a destroyed state) >> --- >> drivers/gpu/drm/panthor/panthor_sched.c | 15 ++++++++++++--- >> 1 file changed, 12 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c >> b/drivers/gpu/drm/panthor/panthor_sched.c >> index 0cc9055f4ee52..4996f987b8183 100644 >> --- a/drivers/gpu/drm/panthor/panthor_sched.c >> +++ b/drivers/gpu/drm/panthor/panthor_sched.c >> @@ -315,6 +315,13 @@ struct panthor_scheduler { >> */ >> struct list_head stopped_groups; >> } reset; >> + >> + /** >> + * @destroyed: Scheduler object is (being) destroyed >> + * >> + * Normal scheduler operations should no longer take place. >> + */ >> + bool destroyed; > > Do we really need a new field for that? Can't we just reset > panthor_device::scheduler to NULL early enough in the unplug path? > I guess it's not that simple if we have works going back to ptdev > and then dereferencing ptdev->scheduler, but I think it's also > fundamentally broken to have scheduler works active after the > scheduler teardown has started, so we might want to add some more > checks in the work callbacks too. > >> }; >> >> /** >> @@ -1765,7 +1772,10 @@ static void process_fw_events_work(struct work_struct >> *work) >> u32 events = atomic_xchg(&sched->fw_events, 0); >> struct panthor_device *ptdev = sched->ptdev; >> >> - mutex_lock(&sched->lock); >> + guard(mutex)(&sched->lock); >> + >> + if (sched->destroyed) >> + return; >> >> if (events & JOB_INT_GLOBAL_IF) { >> sched_process_global_irq_locked(ptdev); >> @@ -1778,8 +1788,6 @@ static void process_fw_events_work(struct work_struct >> *work) >> sched_process_csg_irq_locked(ptdev, csg_id); >> events &= ~BIT(csg_id); >> } >> - >> - mutex_unlock(&sched->lock); >> } >> >> /** >> @@ -3882,6 +3890,7 @@ void panthor_sched_unplug(struct panthor_device *ptdev) >> cancel_delayed_work_sync(&sched->tick_work); >> >> mutex_lock(&sched->lock); >> + sched->destroyed = true; >> if (sched->pm.has_ref) { >> pm_runtime_put(ptdev->base.dev); >> sched->pm.has_ref = false; > > Hm, I'd really like to see a cancel_work_sync(&sched->fw_events_work) > rather than letting the work execute after we've started tearing down > the scheduler object. > > If you follow my suggestion to reset the ptdev->scheduler field, I > guess something like that would do: > > void panthor_sched_unplug(struct panthor_device *ptdev) > { > struct panthor_scheduler *sched = ptdev->scheduler; > > /* We want the schedu */ > WRITE_ONCE(*ptdev->scheduler, NULL); > > cancel_work_sync(&sched->fw_events_work); > cancel_delayed_work_sync(&sched->tick_work); > > mutex_lock(&sched->lock); > if (sched->pm.has_ref) { > pm_runtime_put(ptdev->base.dev); > sched->pm.has_ref = false; > } > mutex_unlock(&sched->lock); > } > > and > > void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events) > { > struct panthor_scheduler *sched = READ_ONCE(*ptdev->scheduler); > > /* Scheduler is not initialized, or it's gone. */ > if (!sched) > return; > > atomic_or(events, &sched->fw_events); > sched_queue_work(sched, fw_events); > }
Note there's also the path of panthor_mmu_irq_handler() calling panthor_sched_report_mmu_fault() which will need to READ_ONCE() as well to be safe. I agree having an extra bool is ugly, but it easier to reason about than the lock-free WRITE_ONCE/READ_ONCE dance. It worries me that this will be regressed in the future. I can't immediately see how to wrap this in a helper to ensure this is kept correct. Thanks, Steve > > > sched_queue_[delayed_]work() could also be automated to issue a drm_WARN_ON() > when it's called and ptdev->scheduler = NULL.
