From: Wen Yang Date: Mon, 1 Jun 2026 15:38:32 +0000 (+0200) Subject: rv: Fix monitor start ordering and memory ordering for monitoring flag X-Git-Tag: v7.1~23^2~12 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=2b9a8c27417eeef01967c6297def426a44776c04;p=thirdparty%2Fkernel%2Flinux.git rv: Fix monitor start ordering and memory ordering for monitoring flag da_monitor_start() set monitoring=1 before calling da_monitor_init_hook(), may racing with the sched_switch handler: da_monitor_start() sched_switch handler ------------------------- --------------------------------- da_mon->monitoring = 1; if (da_monitoring(da_mon)) /* true */ ha_start_timer_ns(...); /* hrtimer->base == NULL, crash */ da_monitor_init_hook(da_mon); /* hrtimer_setup() sets base */ Fix the ordering and pair with release/acquire semantics: da_monitor_init_hook(da_mon); smp_store_release(&da_mon->monitoring, 1); /* da_monitor_start() */ return smp_load_acquire(&da_mon->monitoring); /* da_monitoring() */ On ARM64 a plain STR + LDR does not form a release-acquire pair, so the load can observe monitoring=1 while hrtimer->base is still NULL. The plain accesses are also data races under KCSAN. Use WRITE_ONCE for the monitoring=0 store in da_monitor_reset() to cover the reset path. Fixes: 792575348ff7 ("rv/include: Add deterministic automata monitor definition via C macros") Signed-off-by: Wen Yang Reviewed-by: Gabriele Monaco Reviewed-by: Nam Cao Link: https://lore.kernel.org/r/20260601153840.124372-6-gmonaco@redhat.com Signed-off-by: Gabriele Monaco --- diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h index a7e1036544066..60dc39f2620a2 100644 --- a/include/rv/da_monitor.h +++ b/include/rv/da_monitor.h @@ -82,7 +82,7 @@ static void react(enum states curr_state, enum events event) static inline void da_monitor_reset(struct da_monitor *da_mon) { da_monitor_reset_hook(da_mon); - da_mon->monitoring = 0; + WRITE_ONCE(da_mon->monitoring, 0); da_mon->curr_state = model_get_initial_state(); } @@ -95,8 +95,9 @@ static inline void da_monitor_reset(struct da_monitor *da_mon) static inline void da_monitor_start(struct da_monitor *da_mon) { da_mon->curr_state = model_get_initial_state(); - da_mon->monitoring = 1; da_monitor_init_hook(da_mon); + /* Pairs with smp_load_acquire in da_monitoring(). */ + smp_store_release(&da_mon->monitoring, 1); } /* @@ -104,7 +105,8 @@ static inline void da_monitor_start(struct da_monitor *da_mon) */ static inline bool da_monitoring(struct da_monitor *da_mon) { - return da_mon->monitoring; + /* Pairs with smp_store_release in da_monitor_start(). */ + return smp_load_acquire(&da_mon->monitoring); } /*