Re: [PATCH v7 02/14] rv: Fix ha_monitor timer and invariant underflow
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From: Gabriele Monaco <gmonaco@redhat.com>
Date: 2026-10-26 09:21:54
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On Mon, 2026-10-12 at 03:39 +0800, wen.yang@linux.dev wrote:
From: Wen Yang <redacted>
ha_start_timer_ns() and ha_start_timer_jiffy() compute the remaining
budget as expire - passed. Once the elapsed time passed exceeds the
budget expire (e.g. a state transition after the invariant should have
fired, before the timer callback ran), the unsigned subtraction
underflows to a huge value and the timer is scheduled far into the
future instead of expiring immediately.
ha_check_invariant_ns() computes store >= time_ns - expire_ns, which
underflows when the system uptime is still below expire_ns (a monitor
armed early in boot with a large budget), reporting a false violation.
Clamp the timer remainder to 0 (fire immediately) when passed >= expire,
and replace the invariant check as store + expire_ns >= time_ns so
neither side can underflow.
Fixes: f5587d1b6ec9 ("rv: Add Hybrid Automata monitor type")
Fixes: ab2900ae252b ("rv: Simplify hybrid automata monitors's clock
variables")
Signed-off-by: Wen Yang <redacted>
---Looks good, thanks Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
quoted hunk ↗ jump to hunk
include/rv/ha_monitor.h | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)diff --git a/include/rv/ha_monitor.h b/include/rv/ha_monitor.h index 93ac99ff7f1d..499ce60779f9 100644 --- a/include/rv/ha_monitor.h +++ b/include/rv/ha_monitor.h@@ -351,7 +351,7 @@ static inline void ha_reset_clk_ns(struct ha_monitor*ha_mon, enum envs env, u64 static inline bool ha_check_invariant_ns(struct ha_monitor *ha_mon, enum envs env, u64 time_ns, u64 expire_ns) { - return READ_ONCE(ha_mon->env_store[env]) >= time_ns - expire_ns; + return READ_ONCE(ha_mon->env_store[env]) + expire_ns >= time_ns; } /* * ha_invariant_passed_ns - prepare the invariant and return the time since reset@@ -410,6 +410,11 @@ static inline void ha_inv_to_guard(struct ha_monitor*ha_mon, enum envs env, WRITE_ONCE(ha_mon->env_store[env], READ_ONCE(ha_mon->env_store[env]) - value); } +static inline u64 ha_time_left(u64 passed, u64 expire) +{ + return passed < expire ? expire - passed : 0; +} + #if HA_TIMER_TYPE == HA_TIMER_WHEEL /* * Helper functions to handle the monitor timer.@@ -439,15 +444,17 @@ static inline void ha_start_timer_jiffy(structha_monitor *ha_mon, enum envs env { u64 passed = ha_invariant_passed_jiffy(ha_mon, env, time_ns); - mod_timer(&ha_mon->timer, get_jiffies_64() + expire - passed); + mod_timer(&ha_mon->timer, + get_jiffies_64() + ha_time_left(passed, expire)); } static inline void ha_start_timer_ns(struct ha_monitor *ha_mon, enum envs env, u64 expire, u64 time_ns) { u64 passed = ha_invariant_passed_ns(ha_mon, env, time_ns); + u64 delay = ha_time_left(passed, expire); ha_start_timer_jiffy(ha_mon, ENV_MAX_STORED, - nsecs_to_jiffies(expire - passed + TICK_NSEC - 1), time_ns); + nsecs_to_jiffies(delay + TICK_NSEC - 1), time_ns); } /* * ha_cancel_timer - Cancel the timer@@ -494,7 +501,8 @@ static inline void ha_start_timer_ns(struct ha_monitor*ha_mon, enum envs env, if (RV_MON_TYPE == RV_MON_PER_CPU) mode |= HRTIMER_MODE_PINNED; - hrtimer_start(&ha_mon->hrtimer, ns_to_ktime(expire - passed), mode); + hrtimer_start(&ha_mon->hrtimer, + ns_to_ktime(ha_time_left(passed, expire)), mode); } static inline void ha_start_timer_jiffy(struct ha_monitor *ha_mon, enum envs env, u64 expire, u64 time_ns)@@ -502,7 +510,8 @@ static inline void ha_start_timer_jiffy(struct ha_monitor*ha_mon, enum envs env u64 passed = ha_invariant_passed_jiffy(ha_mon, env, time_ns); ha_start_timer_ns(ha_mon, ENV_MAX_STORED, - jiffies_to_nsecs(expire - passed), time_ns); + jiffies_to_nsecs(ha_time_left(passed, expire)), + time_ns); } /* * ha_cancel_timer - Cancel the timer