Commit aa02cd2d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

xtime_lock vs update_process_times 



Commit d3d74453 ("hrtimer: fixup the
HRTIMER_CB_IRQSAFE_NO_SOFTIRQ fallback") broke several archs, and since
only Russell bothered to merge the fix, and Greg to ACK his arch, I'm
sending this for merger.

I have confirmation that the Alpha bit results in a booting kernel.
That leaves: blackfin, frv, sh and sparc untested.

The deadlock in question was found by Russell:

  IRQ handle
    -> timer_tick() - xtime seqlock held for write
      -> update_process_times()
        -> run_local_timers()
          -> hrtimer_run_queues()
            -> hrtimer_get_softirq_time() - tries to get a read lock

Now, Thomas assures me the fix is trivial, only do_timer() needs to be
done under the xtime_lock, and update_process_times() can savely be
removed from under it.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarGreg Ungerer <gerg@uclinux.org>
CC: Richard Henderson <rth@twiddle.net>
CC: Bryan Wu <bryan.wu@analog.com>
CC: David Howells <dhowells@redhat.com>
CC: Paul Mundt <lethal@linux-sh.org>
CC: William Irwin <wli@holomorphy.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Acked-by: default avatarIvan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 10270d48

arch/alpha/kernel/time.c

+8 −7
Original line number Diff line number Diff line
@@ -119,13 +119,8 @@ irqreturn_t timer_interrupt(int irq, void *dev) 
	state.partial_tick = delta & ((1UL << FIX_SHIFT) - 1); 

	nticks = delta >> FIX_SHIFT;



	while (nticks > 0) {

		do_timer(1);

#ifndef CONFIG_SMP

		update_process_times(user_mode(get_irq_regs()));

#endif

		nticks--;

	}

	if (nticks)

		do_timer(nticks);



	/*

	 * If we have an externally synchronized Linux clock, then update
@@ -141,6 +136,12 @@ irqreturn_t timer_interrupt(int irq, void *dev) 
	}



	write_sequnlock(&xtime_lock);



#ifndef CONFIG_SMP

	while (nticks--)

		update_process_times(user_mode(get_irq_regs()));

#endif



	return IRQ_HANDLED;

}

arch/blackfin/kernel/time.c

+5 −3
Original line number Diff line number Diff line
@@ -137,9 +137,6 @@ irqreturn_t timer_interrupt(int irq, void *dummy) 


	do_timer(1);



#ifndef CONFIG_SMP

	update_process_times(user_mode(get_irq_regs()));

#endif

	profile_tick(CPU_PROFILING);



	/*
@@ -161,6 +158,11 @@ irqreturn_t timer_interrupt(int irq, void *dummy) 
			last_rtc_update = xtime.tv_sec - 600;

	}

	write_sequnlock(&xtime_lock);



#ifndef CONFIG_SMP

	update_process_times(user_mode(get_irq_regs()));

#endif



	return IRQ_HANDLED;

}

arch/frv/kernel/time.c

+4 −2
Original line number Diff line number Diff line
@@ -63,6 +63,7 @@ static irqreturn_t timer_interrupt(int irq, void *dummy) 
	/* last time the cmos clock got updated */

	static long last_rtc_update = 0;



	profile_tick(CPU_PROFILING);

	/*

	 * Here we are in the timer irq handler. We just have irqs locally

	 * disabled but we don't know if the timer_bh is running on the other
@@ -73,8 +74,6 @@ static irqreturn_t timer_interrupt(int irq, void *dummy) 
	write_seqlock(&xtime_lock);



	do_timer(1);

	update_process_times(user_mode(get_irq_regs()));

	profile_tick(CPU_PROFILING);



	/*

	 * If we have an externally synchronized Linux clock, then update
@@ -99,6 +98,9 @@ static irqreturn_t timer_interrupt(int irq, void *dummy) 
#endif /* CONFIG_HEARTBEAT */



	write_sequnlock(&xtime_lock);



	update_process_times(user_mode(get_irq_regs()));



	return IRQ_HANDLED;

}

arch/m68knommu/kernel/time.c

+7 −5
Original line number Diff line number Diff line
@@ -42,14 +42,12 @@ irqreturn_t arch_timer_interrupt(int irq, void *dummy) 
	/* last time the cmos clock got updated */

	static long last_rtc_update=0;



	if (current->pid)

		profile_tick(CPU_PROFILING);



	write_seqlock(&xtime_lock);



	do_timer(1);

#ifndef CONFIG_SMP

	update_process_times(user_mode(get_irq_regs()));

#endif

	if (current->pid)

		profile_tick(CPU_PROFILING);



	/*

	 * If we have an externally synchronized Linux clock, then update
@@ -67,6 +65,10 @@ irqreturn_t arch_timer_interrupt(int irq, void *dummy) 
	}



	write_sequnlock(&xtime_lock);



#ifndef CONFIG_SMP

	update_process_times(user_mode(get_irq_regs()));

#endif

	return(IRQ_HANDLED);

}

arch/sh/kernel/timers/timer-cmt.c

+0 −9
Original line number Diff line number Diff line
@@ -100,16 +100,7 @@ static irqreturn_t cmt_timer_interrupt(int irq, void *dev_id) 
	timer_status &= ~0x80;

	ctrl_outw(timer_status, CMT_CMCSR_0);



	/*

	 * Here we are in the timer irq handler. We just have irqs locally

	 * disabled but we don't know if the timer_bh is running on the other

	 * CPU. We need to avoid to SMP race with it. NOTE: we don' t need

	 * the irq version of write_lock because as just said we have irq

	 * locally disabled. -arca

	 */

	write_seqlock(&xtime_lock);

	handle_timer_tick();

	write_sequnlock(&xtime_lock);



	return IRQ_HANDLED;

}

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