From 7285dd7fd375763bfb8ab1ac9cf3f1206f503c16 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 28 Aug 2009 20:25:24 +0200 Subject: clocksource: Resolve cpu hotplug dead lock with TSC unstable Martin Schwidefsky analyzed it: 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. The solution is to replace the TSC via the clocksource watchdog mechanism. Mark the TSC as unstable and schedule the watchdog work so it gets removed in the watchdog thread context. Signed-off-by: Thomas Gleixner LKML-Reference: Cc: Martin Schwidefsky Cc: John Stultz --- arch/x86/kernel/tsc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'arch') diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 968425422c46..fc3672a303d6 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -767,12 +767,14 @@ void mark_tsc_unstable(char *reason) { if (!tsc_unstable) { tsc_unstable = 1; - printk("Marking TSC unstable due to %s\n", reason); + printk(KERN_INFO "Marking TSC unstable due to %s\n", reason); /* Change only the rating, when not registered */ if (clocksource_tsc.mult) - clocksource_change_rating(&clocksource_tsc, 0); - else + clocksource_mark_unstable(&clocksource_tsc); + else { + clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE; clocksource_tsc.rating = 0; + } } } -- cgit v1.2.3