* Re: timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree
@ 2011-03-11 13:50 Oleg Nesterov
[not found] ` <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
0 siblings, 1 reply; 3+ messages in thread
From: Oleg Nesterov @ 2011-03-11 13:50 UTC (permalink / raw)
To: Alexander Shishkin
Cc: Thomas Gleixner, Alexander Viro, Greg Kroah-Hartman, Feng Tang,
Michael Tokarev, Marcelo Tosatti, John Stultz, Chris Friesen,
Kay Sievers, Kirill A. Shutemov, Artem Bityutskiy, Davide Libenzi,
Michael Kerrisk, linux-api-u79uwXL29TY76Z2rM5mHXA, Andrew Morton,
linux-kernel-u79uwXL29TY76Z2rM5mHXA
> @@ -218,10 +266,12 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf
> * it to the new values.
> */
> for (;;) {
> + spin_lock(¬ifiers_lock);
> spin_lock_irq(&ctx->wqh.lock);
> - if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
> + if (!list_empty(¬ifiers_list) || hrtimer_try_to_cancel(&ctx->tmr) >= 0)
> break;
Confused. Why do we check the global notifiers_list?
IOW. Suppose that this list is not empty and timerfd_settime() is called
without TFD_NOTIFY_CLOCK_SET. Now we are going to reprogramm the timer
without stopping it?
And. What if timerfd_settime(TFD_NOTIFY_CLOCK_SET, utmr => NULL) is called
twice? timerfd_setup() blindly does list_add(), and we corrupt the list, no?
Oleg.
^ permalink raw reply [flat|nested] 3+ messages in thread[parent not found: <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]
* Re: timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree [not found] ` <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> @ 2011-03-11 15:08 ` Alexander Shishkin 2011-03-11 16:23 ` Thomas Gleixner 1 sibling, 0 replies; 3+ messages in thread From: Alexander Shishkin @ 2011-03-11 15:08 UTC (permalink / raw) To: Oleg Nesterov Cc: Thomas Gleixner, Alexander Viro, Greg Kroah-Hartman, Feng Tang, Michael Tokarev, Marcelo Tosatti, John Stultz, Chris Friesen, Kay Sievers, Kirill A. Shutemov, Artem Bityutskiy, Davide Libenzi, Michael Kerrisk, linux-api-u79uwXL29TY76Z2rM5mHXA, Andrew Morton, linux-kernel-u79uwXL29TY76Z2rM5mHXA, Alexander Shishkin On Fri, Mar 11, 2011 at 02:50:23PM +0100, Oleg Nesterov wrote: > > @@ -218,10 +266,12 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf > > * it to the new values. > > */ > > for (;;) { > > + spin_lock(¬ifiers_lock); > > spin_lock_irq(&ctx->wqh.lock); > > - if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) > > + if (!list_empty(¬ifiers_list) || hrtimer_try_to_cancel(&ctx->tmr) >= 0) > > break; > > Confused. Why do we check the global notifiers_list? You're right, it's a bug, should be &ctx->notifiers_list. > IOW. Suppose that this list is not empty and timerfd_settime() is called > without TFD_NOTIFY_CLOCK_SET. Now we are going to reprogramm the timer > without stopping it? > > And. What if timerfd_settime(TFD_NOTIFY_CLOCK_SET, utmr => NULL) is called > twice? timerfd_setup() blindly does list_add(), and we corrupt the list, no? Another catch. There will be a quite a bit of rework required, though, considering tglx's comments. Thanks! -- Alex ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree [not found] ` <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2011-03-11 15:08 ` Alexander Shishkin @ 2011-03-11 16:23 ` Thomas Gleixner 1 sibling, 0 replies; 3+ messages in thread From: Thomas Gleixner @ 2011-03-11 16:23 UTC (permalink / raw) To: Oleg Nesterov Cc: Alexander Shishkin, Alexander Viro, Greg Kroah-Hartman, Feng Tang, Michael Tokarev, Marcelo Tosatti, John Stultz, Chris Friesen, Kay Sievers, Kirill A. Shutemov, Artem Bityutskiy, Davide Libenzi, Michael Kerrisk, linux-api-u79uwXL29TY76Z2rM5mHXA, Andrew Morton, linux-kernel-u79uwXL29TY76Z2rM5mHXA On Fri, 11 Mar 2011, Oleg Nesterov wrote: > > @@ -218,10 +266,12 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf > > * it to the new values. > > */ > > for (;;) { > > + spin_lock(¬ifiers_lock); > > spin_lock_irq(&ctx->wqh.lock); > > - if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) > > + if (!list_empty(¬ifiers_list) || hrtimer_try_to_cancel(&ctx->tmr) >= 0) > > break; > > Confused. Why do we check the global notifiers_list? > > IOW. Suppose that this list is not empty and timerfd_settime() is called > without TFD_NOTIFY_CLOCK_SET. Now we are going to reprogramm the timer > without stopping it? > > And. What if timerfd_settime(TFD_NOTIFY_CLOCK_SET, utmr => NULL) is called > twice? timerfd_setup() blindly does list_add(), and we corrupt the list, no? And why is this hack in -mm at all ? Thanks, tglx ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-03-11 16:23 UTC | newest]
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2011-03-11 13:50 timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree Oleg Nesterov
[not found] ` <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2011-03-11 15:08 ` Alexander Shishkin
2011-03-11 16:23 ` Thomas Gleixner
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