| From | Thomas Gleixner <> | Subject | [patch 06/20] posix-timers: Annotate concurrent access to k_itimer::it_signal | Date | Tue, 25 Apr 2023 20:49:05 +0200 (CEST) |
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k_itimer::it_signal is read lockless in the RCU protected hash lookup, but it can be written concurrently in the timer_create() and timer_delete() path. Annotate these places with READ_ONCE() and WRITE_ONCE()
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- kernel/time/posix-timers.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
--- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -109,9 +109,9 @@ static struct k_itimer *__posix_timers_f { struct k_itimer *timer; - hlist_for_each_entry_rcu(timer, head, t_hash, - lockdep_is_held(&hash_lock)) { - if ((timer->it_signal == sig) && (timer->it_id == id)) + hlist_for_each_entry_rcu(timer, head, t_hash, lockdep_is_held(&hash_lock)) { + /* timer->it_signal can be set concurrently */ + if ((READ_ONCE(timer->it_signal) == sig) && (timer->it_id == id)) return timer; } return NULL; @@ -557,7 +557,7 @@ static int do_timer_create(clockid_t whi spin_lock_irq(¤t->sighand->siglock); /* This makes the timer valid in the hash table */ - new_timer->it_signal = current->signal; + WRITE_ONCE(new_timer->it_signal, current->signal); list_add(&new_timer->list, ¤t->signal->posix_timers); spin_unlock_irq(¤t->sighand->siglock); @@ -1051,10 +1051,10 @@ SYSCALL_DEFINE1(timer_delete, timer_t, t list_del(&timer->list); spin_unlock(¤t->sighand->siglock); /* - * This keeps any tasks waiting on the spin lock from thinking - * they got something (see the lock code above). + * A concurrent lookup could check timer::it_signal lockless. It + * will reevaluate with timer::it_lock held and observe the NULL. */ - timer->it_signal = NULL; + WRITE_ONCE(timer->it_signal, NULL); unlock_timer(timer, flags); release_posix_timer(timer, IT_ID_SET);
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