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xtime_lock vs update_process_times

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Commit d3d74453c3 ("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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Greg 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: Ingo Molnar <mingo@elte.hu>
Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra
2008-02-13 21:33:16 +01:00
committed by Linus Torvalds
parent 10270d4838
commit aa02cd2d9b
8 changed files with 28 additions and 33 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
arch/frv/kernel/time.c
View File

@@ -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;
}