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Date: Sat, 22 Aug 2009 23:14:57 +0200 From: Martin Schwidefsky <schwidefsky@...ibm.com> To: Ingo Molnar <mingo@...e.hu> Cc: mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org, johnstul@...ibm.com, tglx@...utronix.de, linux-tip-commits@...r.kernel.org Subject: Re: [tip:timers/core] x86: Do not unregister PIT clocksource on PIT oneshot setup/shutdown On Sat, 22 Aug 2009 12:35:41 +0200 Ingo Molnar <mingo@...e.hu> wrote: > even after this fix, -tip testing found yet another circular locking > bug, on a 32-bit Core2 laptop: You got to love lockdep .. another ugly one: clocksource_register: has clocksource_mutex, get cpu_add_remove_lock native_cpu_up: has cpu_add_remove_lock, get clocksource_mutex To register a clocksource the clocksource_mutex is acquired and if necessary timekeeping_notify is called to install the clocksource as the timekeeper clock. timekeeping_notify uses stop_machine which needs to take cpu_add_remove_lock mutex. Starting a new cpu is done with the cpu_add_remove_lock mutex held. native_cpu_up checks the tsc of the new cpu and if the tsc is no good clocksource_change_rating is called. Which needs the clocksource_mutex and the deadlock is complete. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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