| Submitter | Luis Henriques |
|---|---|
| Date | Feb. 26, 2013, 4:13 p.m. |
| Message ID | <1361895211-28023-1-git-send-email-luis.henriques@canonical.com> |
| Download | mbox | patch |
| Permalink | /patch/223308/ |
| State | New |
| Headers | show |
Comments
Patch
diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c index 27d186a..6bbf936 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); }
This is a note to let you know that I have just added a patch titled ARM: 7643/1: sched: correct update_sched_clock() to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 50a9827bffa5ddd18f72f5b09526775c1b9e068d Mon Sep 17 00:00:00 2001 From: Joonsoo Kim <js1304@gmail.com> Date: Sat, 9 Feb 2013 05:52:45 +0100 Subject: [PATCH] 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: Luis Henriques <luis.henriques@canonical.com> --- arch/arm/kernel/sched_clock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 1.8.1.2