From 3b950de9c94b4b9fde4f1340358ab52ce0f34be0 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 27 Oct 2010 17:28:35 +0100 Subject: [PATCH] MN10300: Prevent cnt32_to_63() from being preempted in sched_clock() Prevent cnt32_to_63() from being preempted in sched_clock() because it may read its internal counter, get preempted, get delayed for more than the half period of the 'TSC' and then write the internal counter, thus corrupting it. Whilst some callers of sched_clock() have interrupts disabled or hold spinlocks, not all do, and so preemption must be held here. Note that sched_clock() is called from lockdep, but that shouldn't be a problem because although preempt_disable() calls into lockdep, lockdep has a recursion counter to deal with this. Signed-off-by: David Howells --- arch/mn10300/kernel/time.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/mn10300/kernel/time.c b/arch/mn10300/kernel/time.c index 8f7f6d22783..0b5c856b426 100644 --- a/arch/mn10300/kernel/time.c +++ b/arch/mn10300/kernel/time.c @@ -54,6 +54,9 @@ unsigned long long sched_clock(void) unsigned long tsc, tmp; unsigned product[3]; /* 96-bit intermediate value */ + /* cnt32_to_63() is not safe with preemption */ + preempt_disable(); + /* read the TSC value */ tsc = 0 - get_cycles(); /* get_cycles() counts down */ @@ -64,6 +67,8 @@ unsigned long long sched_clock(void) */ tsc64.ll = cnt32_to_63(tsc) & 0x7fffffffffffffffULL; + preempt_enable(); + /* scale the 64-bit TSC value to a nanosecond value via a 96-bit * intermediate */ -- 2.39.2