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authorGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-04-14 18:21:35 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-04-14 18:21:35 -0700
commit2f093e2aa466d799c0952bfd1c6c68ff5d80fc17 (patch)
treee3d511aca536b7123d256b98a0ef8e74fc219498 /kernel/sched/clock.c
parenta7761027656dc192b59617a6eb961e38097419ce (diff)
parent41ef2d5678d83af030125550329b6ae8b74618fa (diff)
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Merge 3.9-rc7 into char-misc-next
We want the fixes in there. Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/sched/clock.c')
-rw-r--r--kernel/sched/clock.c26
1 files changed, 26 insertions, 0 deletions
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index c685e31492df..c3ae1446461c 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -176,10 +176,36 @@ static u64 sched_clock_remote(struct sched_clock_data *scd)
u64 this_clock, remote_clock;
u64 *ptr, old_val, val;
+#if BITS_PER_LONG != 64
+again:
+ /*
+ * Careful here: The local and the remote clock values need to
+ * be read out atomic as we need to compare the values and
+ * then update either the local or the remote side. So the
+ * cmpxchg64 below only protects one readout.
+ *
+ * We must reread via sched_clock_local() in the retry case on
+ * 32bit as an NMI could use sched_clock_local() via the
+ * tracer and hit between the readout of
+ * the low32bit and the high 32bit portion.
+ */
+ this_clock = sched_clock_local(my_scd);
+ /*
+ * We must enforce atomic readout on 32bit, otherwise the
+ * update on the remote cpu can hit inbetween the readout of
+ * the low32bit and the high 32bit portion.
+ */
+ remote_clock = cmpxchg64(&scd->clock, 0, 0);
+#else
+ /*
+ * On 64bit the read of [my]scd->clock is atomic versus the
+ * update, so we can avoid the above 32bit dance.
+ */
sched_clock_local(my_scd);
again:
this_clock = my_scd->clock;
remote_clock = scd->clock;
+#endif
/*
* Use the opportunity that we have both locks