[PATCH] ia32 sched_clock() deadlock fix

From: Ingo Molnar <mingo@elte.hu>,

Voyager is getting odd deadlocks due to the taking of xtime_lock() in
sched_clock()->get_jiffies_64().

I had this patch queued up to fix a different deadlock, which occurs when we
relax the requirement that TSC's be synchronised across CPUs.  But it will
fix James' deadlock too.

diff --git a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
index 0030d7989fea308a4549a296f4ea665553c4b7c8..cafc53150595d9d6021836909ea85b55bceeaee8 100644 (file)
--- a/arch/i386/kernel/timers/timer_tsc.c
+++ b/arch/i386/kernel/timers/timer_tsc.c
@@ -140,7 +140,8 @@ unsigned long long sched_clock(void)
 #ifndef CONFIG_NUMA
        if (!use_tsc)
 #endif
-               return (unsigned long long)get_jiffies_64() * (1000000000 / HZ);
+               /* no locking but a rare wrong value is not a big deal */
+               return jiffies_64 * (1000000000 / HZ);
 
        /* Read the Time Stamp Counter */
        rdtscll(this_offset);