Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch 09/45] posix-cpu-timers: Fix posix_cpu_timer_get() behaviour | Date | Thu, 29 Jun 2023 20:14:49 +0200 |
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On Tue, Jun 27 2023 at 00:46, Frederic Weisbecker wrote:> On Tue, Jun 06, 2023 at 04:37:33PM +0200, Thomas Gleixner wrote: >> Aside of that posix_cpu_timer_set() pointlessly arms SIGEV_NONE timers >> which are later disarmed when the initial expiry happens. That's bogus and >> just keeping the process wide timer active for nothing. >> >> Cure this by: >> >> 1) Avoiding to arm SIGEV_NONE timers >> >> 2) Forwarding interval timers in posix_cpu_timer_get() >> >> 3) Taking SIGEV_NONE into account when a oneshot timer has expired > > This patch does too many things at once...
Let me try again to split it up. I failed before ...
>> -static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp) >> +static void __posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp, u64 now) >> { >> - clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock); >> - struct cpu_timer *ctmr = &timer->it.cpu; >> - u64 now, expires = cpu_timer_getexpires(ctmr); >> - struct task_struct *p; >> - >> - rcu_read_lock(); >> - p = cpu_timer_task_rcu(timer); >> - if (!p) >> - goto out; >> + bool sigev_none = timer->it_sigev_notify == SIGEV_NONE; >> + u64 expires; >> >> /* >> - * Easy part: convert the reload time. >> + * Make sure that interval timers are moved forward for the >> + * following cases: >> + * - SIGEV_NONE timers which are never armed >> + * - Timers which expired, but the signal has not yet been >> + * delivered >> */ >> - itp->it_interval = ktime_to_timespec64(timer->it_interval); >> - >> - if (!expires) >> - goto out; >> + expires = bump_cpu_timer(timer, now); > > What if the expiration has been reached but we arrived here before > handle_posix_cpu_timers() had a chance? In that case the call to > bump_cpu_timer() may forward the timer and artificially create an > overrun / missed event.
Bah. This clearly misses some conditionals so that it actually handles the cases described in the comment above it...
Thanks,
tglx
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