• Peter Zijlstra's avatar
    xtime_lock vs update_process_times · aa02cd2d
    Peter Zijlstra authored
    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>
    aa02cd2d
pcic.c 26.4 KB