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| author | Joonsoo Kim <js1304@gmail.com> | 2013-02-09 08:52:45 +0400 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2013-02-11 21:33:08 +0400 |
| commit | 7c4e9ced424be4d36df6a3e3825763e97ee97607 (patch) | |
| tree | d4d7622944fb13565d3b4409de9950477c9570a1 /arch/arm | |
| parent | 836dc9e3fbbab0c30aa6e664417225f5c1fb1c39 (diff) | |
| download | linux-7c4e9ced424be4d36df6a3e3825763e97ee97607.tar.xz | |
ARM: 7643/1: sched: correct update_sched_clock()
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.
Cc: <stable@vger.kernel.org>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm')
| -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 fc6692e2b603..bd6f56b9ec21 100644 --- a/arch/arm/kernel/sched_clock.c +++ b/arch/arm/kernel/sched_clock.c @@ -93,11 +93,11 @@ 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); } |