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authorDave Kleikamp <shaggy@linux.vnet.ibm.com>2008-10-09 14:21:30 -0400
committerIngo Molnar <mingo@elte.hu>2008-10-10 05:17:04 -0400
commit5b7dba4ff834259a5623e03a565748704a8fe449 (patch)
tree8fa9be3a308d1b5f2eb22d0a02dbe887a479ee3e /kernel
parenta5d8c3483a6e19aca95ef6a2c5890e33bfa5b293 (diff)
sched_clock: prevent scd->clock from moving backwards
When sched_clock_cpu() couples the clocks between two cpus, it may increment scd->clock beyond the GTOD tick window that __update_sched_clock() uses to clamp the clock. A later call to __update_sched_clock() may move the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's monotonic property. This patch ensures that scd->clock will not be set backward. Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched_clock.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index e8ab096ddfe3..81787248b60f 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -118,13 +118,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
118 118
119 /* 119 /*
120 * scd->clock = clamp(scd->tick_gtod + delta, 120 * scd->clock = clamp(scd->tick_gtod + delta,
121 * max(scd->tick_gtod, scd->clock), 121 * max(scd->tick_gtod, scd->clock),
122 * scd->tick_gtod + TICK_NSEC); 122 * max(scd->clock, scd->tick_gtod + TICK_NSEC));
123 */ 123 */
124 124
125 clock = scd->tick_gtod + delta; 125 clock = scd->tick_gtod + delta;
126 min_clock = wrap_max(scd->tick_gtod, scd->clock); 126 min_clock = wrap_max(scd->tick_gtod, scd->clock);
127 max_clock = scd->tick_gtod + TICK_NSEC; 127 max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);
128 128
129 clock = wrap_max(clock, min_clock); 129 clock = wrap_max(clock, min_clock);
130 clock = wrap_min(clock, max_clock); 130 clock = wrap_min(clock, max_clock);