From 1be396794897f80bfc8774719ba60309a9e3d374 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Fri, 14 Aug 2009 15:47:20 +0200 Subject: timekeeping: Move reset of cycle_last for tsc clocksource to tsc change_clocksource resets the cycle_last value to zero then sets it to a value read from the clocksource. The reset to zero is required only for the TSC clocksource to make the read_tsc function work after a resume. The reason is that the TSC read function uses cycle_last to detect backwards going TSCs. In the resume case cycle_last contains the TSC value from the last update before the suspend. On resume the TSC starts counting from 0 again and would trip over the cycle_last comparison. This is subtle and surprising. Move the reset to a resume function in the tsc code. Signed-off-by: Martin Schwidefsky Acked-by: Thomas Gleixner Acked-by: John Stultz Cc: Daniel Walker LKML-Reference: <20090814134808.142191175@de.ibm.com> Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tsc.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/x86/kernel/tsc.c') diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 71f4368b357e..968425422c46 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(void) } #endif +static void resume_tsc(void) +{ + clocksource_tsc.cycle_last = 0; +} + static struct clocksource clocksource_tsc = { .name = "tsc", .rating = 300, .read = read_tsc, + .resume = resume_tsc, .mask = CLOCKSOURCE_MASK(64), .shift = 22, .flags = CLOCK_SOURCE_IS_CONTINUOUS | -- cgit v1.2.2 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/x86/kernel/tsc.c') 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 v1.2.2