Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues: - [High] Non-synchronous timer cancellation combined with `synchronize_rcu()` or `kfree_rcu()` leads to a Use-After-Free during monitor teardown. -- --- Patch [5]: [PATCH v6 5/9] rv: Make da_monitor_reset_hook and EVENT_NONE_LBL overridable --- commit 693c5f5465506e090a4b8b44d5e3c72769ec0685 Author: Wen Yang <[email protected]> rv: Make da_monitor_reset_hook and EVENT_NONE_LBL overridable This commit wraps da_monitor_reset_hook and EVENT_NONE_LBL with ifndef guards to allow HA-based monitors to provide their own implementations. It enables monitors like tlob to define custom reset hooks for tasks such as cancelling per-task hrtimers. > diff --git a/include/rv/ha_monitor.h b/include/rv/ha_monitor.h > index e1738d199b289..807b981eb548a 100644 > --- a/include/rv/ha_monitor.h > +++ b/include/rv/ha_monitor.h > @@ -36,8 +36,14 @@ static bool ha_monitor_handle_constraint(struct da_monitor > *da_mon, > da_id_type id); > #define da_monitor_event_hook ha_monitor_handle_constraint > #define da_monitor_init_hook ha_monitor_init_env > + > +/* Overrides must still call ha_monitor_reset_env() or cancel the timer. */ > +#ifndef da_monitor_reset_hook > #define da_monitor_reset_hook ha_monitor_reset_env > +#endif > +#ifndef da_monitor_sync_hook > #define da_monitor_sync_hook() synchronize_rcu() > +#endif [Severity: High] This isn't a bug introduced by this patch, but is it safe to rely on synchronize_rcu() to wait for cancelled timers during monitor teardown? Looking at the global teardown path: include/rv/da_monitor.h:da_monitor_destroy() { ... da_monitor_reset_all(); da_monitor_sync_hook(); ... } And per-object teardown: include/rv/da_monitor.h:da_destroy_storage() { ... da_monitor_reset_hook(&mon_storage->rv.da_mon); hash_del_rcu(&mon_storage->node); if (DA_MON_ALLOCATION_STRATEGY == DA_ALLOC_POOL) call_rcu(&mon_storage->rcu, da_pool_return_cb); else kfree_rcu(mon_storage, rcu); ... } Both paths cancel timers non-synchronously in ha_monitor_reset_env(): include/rv/ha_monitor.h:ha_monitor_reset_env() { ... ha_cancel_timer(ha_mon); ... } They then rely on RCU grace periods to wait for executing callbacks, assuming the callbacks execute within an RCU read-side critical section: include/rv/ha_monitor.h:__ha_monitor_timer_callback() { ... guard(rcu)(); ... } If the timer callback is dispatched but preempted or delayed before entering its RCU read-side critical section, synchronize_rcu() will not wait for it. When the callback resumes, couldn't it access the freed monitor storage and cause a use-after-free? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=5
