diff options
| author | Joonsoo Kim <js1304@gmail.com> | 2013-02-09 05:52:45 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-02-28 06:59:04 -0800 |
| commit | 27c303244ef8049be6fd8088230c7f5e02a522b3 (patch) | |
| tree | ccb85f0306747f1b44f919fc798d36bc70d2cd1e | |
| parent | cae53e2a9a03e53152fdd331067923f7d65fc72e (diff) | |
ARM: 7643/1: sched: correct update_sched_clock()
commit 7c4e9ced424be4d36df6a3e3825763e97ee97607 upstream.
If we want load epoch_cyc and epoch_ns atomically,
we should update epoch_cyc_copy first of all.
This notify reader that updating is in progress.
If we update epoch_cyc first like as current implementation,
there is subtle error case.
Look at the below example.
<Initial Condition>
cyc = 9
ns = 900
cyc_copy = 9
== CASE 1 ==
<CPU A = reader> <CPU B = updater>
write cyc = 10
read cyc = 10
read ns = 900
write ns = 1000
write cyc_copy = 10
read cyc_copy = 10
output = (10, 900)
== CASE 2 ==
<CPU A = reader> <CPU B = updater>
read cyc = 9
write cyc = 10
write ns = 1000
read ns = 1000
read cyc_copy = 9
write cyc_copy = 10
output = (9, 1000)
If atomic read is ensured, output should be (9, 900) or (10, 1000).
But, output in example case are not.
So, change updating sequence in order to correct this problem.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/arm/kernel/sched_clock.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c index 27d186abbc06..6bbf936b8354 100644 --- a/arch/arm/kernel/sched_clock.c +++ b/arch/arm/kernel/sched_clock.c @@ -84,11 +84,11 @@ static void notrace update_sched_clock(void) * detectable in cyc_to_fixed_sched_clock(). */ raw_local_irq_save(flags); - cd.epoch_cyc = cyc; + cd.epoch_cyc_copy = cyc; smp_wmb(); cd.epoch_ns = ns; smp_wmb(); - cd.epoch_cyc_copy = cyc; + cd.epoch_cyc = cyc; raw_local_irq_restore(flags); } |