linux-kernel - Re: tip/master merge problem?

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Message-ID: <20090102160621.GE1180@elte.hu>
Date:	Fri, 2 Jan 2009 17:06:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: tip/master merge problem?


* Mike Travis <travis@....com> wrote:

> 
> Hi Ingo,
> 
> I found this code snippet in kernel/sched.c in the tip/master tree.  It
> appears to be a merge mistake:  (cut and pasted - no tabs)
> 
> 292                 /*
> 293                  * If this cpu is the one which updates jiffies, then
> 294                  * give up the assignment and let it be taken by the
> 295                  * cpu which runs the tick timer next, which might be
> 296                  * this cpu as well. If we don't drop this here the
> 297                  * jiffies might be stale and do_timer() never
> 298                  * invoked.
> 299                  */
> 300                 if (cpu == tick_do_timer_cpu)
> 301                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
> 302
> 303                 if (delta_jiffies > 1)
> 304
> 305                 /* Skip reprogram of event if its not changed */
> 306                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
> 307                         goto out;
> 308
> 309                         cpumask_set_cpu(cpu, nohz_cpu_mask);
> 
> I think the "Skip reprogram" was inserted into the middle of a previous
> if-then statement.

indeed, this is plain broken. It happened to build and boot but still it's 
broken.

> git blames it on:
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 292)              /*
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 293)               * If this cpu is the one which updates jiffies, then
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 294)               * give up the assignment and let it be taken by the
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 295)               * cpu which runs the tick timer next, which might be
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 296)               * this cpu as well. If we don't drop this here the
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 297)               * jiffies might be stale and do_timer() never
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 298)               * invoked.
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 299)               */
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 300)              if (cpu == tick_do_timer_cpu)
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 301)                      tick_do_timer_cpu = TICK_DO_TIMER_NONE;
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 302)
> 6ba9b346 (Ingo Molnar       2007-02-19 18:11:56 +0000 303)              if (delta_jiffies > 1)
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 304)
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 305)              /* Skip reprogram of event if its not changed */
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 306)              if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 307)                      goto out;
> 00147449 (Woodruff, Richard 2008-12-01 14:18:11 -0800 308)
> 6a7b3dc3 (Rusty Russell     2008-11-25 02:35:04 +1030 309)                      cpumask_set_cpu(cpu, nohz_cpu_mask);
> 
> I've Cc'd both interested parties.

purely my fault. I've zapped that conflict resolution and picked up yours.

	Ingo
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