From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261412AbTDKSmo (for ); Fri, 11 Apr 2003 14:42:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261454AbTDKSmo (for ); Fri, 11 Apr 2003 14:42:44 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:54262 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id S261412AbTDKSmk (for ); Fri, 11 Apr 2003 14:42:40 -0400 Message-ID: <3E970F37.7040409@mvista.com> Date: Fri, 11 Apr 2003 11:53:43 -0700 From: george anzinger User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrew Morton CC: davidm@hpl.hp.com, linux-kernel@vger.kernel.org Subject: Re: too much timer simplification... References: <200304110705.h3B75aQt026081@napali.hpl.hp.com> <20030411002816.786296e8.akpm@digeo.com> In-Reply-To: <20030411002816.786296e8.akpm@digeo.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > David Mosberger wrote: > >>It appears to me that this changeset: >> >> http://linux.bkbits.net:8080/linux-2.5/diffs/kernel/timer.c@1.48 >> >>may have gone a little too far. >> >>What I'm seeing is that if someone happens to arm a periodic timer at >>exactly 256 jiffies (as ohci happens to do on platforms with HZ=1024), >>then you end up getting an endless loop of timer activations, causing >>a machine hang. >> >>The problem is that __run_timers updates base->timer_jiffies _before_ >>running the callback routines. If a callback re-arms the timer at >>exactly 256 jiffies, add_timers() will reinsert the timer into the >>list that we're currently processing, which of course will cause the >>timer to expire immediately again, etc., etc., ad naseum... >> > > > OK, well unless George can pull a rabbit out of the hat it may > be best to just revert it. > I think the answer here is to move the whole expired list to a local header and to not look back. I will work this into a patch... -g > This gives us the same algorithm as 2.4, which I think is good. > > > --- 25/kernel/timer.c~timer-simplification-revert 2003-04-11 00:19:48.000000000 -0700 > +++ 25-akpm/kernel/timer.c 2003-04-11 00:19:48.000000000 -0700 > @@ -56,6 +56,7 @@ struct tvec_t_base_s { > spinlock_t lock; > unsigned long timer_jiffies; > struct timer_list *running_timer; > + struct list_head *run_timer_list_running; > tvec_root_t tv1; > tvec_t tv2; > tvec_t tv3; > @@ -100,6 +101,12 @@ static inline void check_timer(struct ti > check_timer_failed(timer); > } > > +/* > + * If a timer handler re-adds the timer with expires == jiffies, the timer > + * running code can lock up. So here we detect that situation and park the > + * timer onto base->run_timer_list_running. It will be added to the main timer > + * structures later, by __run_timers(). > + */ > > static void internal_add_timer(tvec_base_t *base, struct timer_list *timer) > { > @@ -107,7 +114,9 @@ static void internal_add_timer(tvec_base > unsigned long idx = expires - base->timer_jiffies; > struct list_head *vec; > > - if (idx < TVR_SIZE) { > + if (base->run_timer_list_running) { > + vec = base->run_timer_list_running; > + } else if (idx < TVR_SIZE) { > int i = expires & TVR_MASK; > vec = base->tv1.vec + i; > } else if (idx < 1 << (TVR_BITS + TVN_BITS)) { > @@ -397,6 +406,7 @@ static inline void __run_timers(tvec_bas > > spin_lock_irq(&base->lock); > while (time_after_eq(jiffies, base->timer_jiffies)) { > + LIST_HEAD(deferred_timers); > struct list_head *head; > int index = base->timer_jiffies & TVR_MASK; > > @@ -408,7 +418,7 @@ static inline void __run_timers(tvec_bas > (!cascade(base, &base->tv3, INDEX(1))) && > !cascade(base, &base->tv4, INDEX(2))) > cascade(base, &base->tv5, INDEX(3)); > - ++base->timer_jiffies; > + base->run_timer_list_running = &deferred_timers; > repeat: > head = base->tv1.vec + index; > if (!list_empty(head)) { > @@ -427,6 +437,14 @@ repeat: > spin_lock_irq(&base->lock); > goto repeat; > } > + base->run_timer_list_running = NULL; > + ++base->timer_jiffies; > + while (!list_empty(&deferred_timers)) { > + timer = list_entry(deferred_timers.prev, > + struct timer_list, entry); > + list_del(&timer->entry); > + internal_add_timer(base, timer); > + } > } > set_running_timer(base, NULL); > spin_unlock_irq(&base->lock); > > _ > > -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml