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authorFrederic Weisbecker <fweisbec@gmail.com>2013-07-13 17:10:18 +0200
committerFrederic Weisbecker <fweisbec@gmail.com>2013-08-14 17:14:50 +0200
commit54461562c90e0ac104764c5a9de637fd9151a1c1 (patch)
treedf04e7b576eb54a29e80f9827c73d473c87ec0bf /kernel/sched/cputime.c
parent7621d1f8bcb418e7a7ac583e89e38ec01b7ed182 (diff)
downloadop-kernel-dev-54461562c90e0ac104764c5a9de637fd9151a1c1.zip
op-kernel-dev-54461562c90e0ac104764c5a9de637fd9151a1c1.tar.gz
vtime: Fix racy cputime delta update
get_vtime_delta() must be called under the task vtime_seqlock with the code that does the cputime accounting flush. Otherwise the cputime reader can be fooled and run into a race where it sees the snapshot update but misses the cputime flush. As a result it can report a cputime that is way too short. Fix vtime_account_user() that wasn't complying to that rule. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Kevin Hilman <khilman@linaro.org>
Diffstat (limited to 'kernel/sched/cputime.c')
-rw-r--r--kernel/sched/cputime.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 5f273b47..b62d5c0 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -683,9 +683,10 @@ void vtime_account_irq_exit(struct task_struct *tsk)
void vtime_account_user(struct task_struct *tsk)
{
- cputime_t delta_cpu = get_vtime_delta(tsk);
+ cputime_t delta_cpu;
write_seqlock(&tsk->vtime_seqlock);
+ delta_cpu = get_vtime_delta(tsk);
tsk->vtime_snap_whence = VTIME_SYS;
account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
write_sequnlock(&tsk->vtime_seqlock);
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