Commit-ID: 54461562c90e0ac104764c5a9de637fd9151a1c1
Gitweb: http://git.kernel.org/tip/54461562c90e0ac104764c5a9de637fd9151a1c1
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Sat, 13 Jul 2013 17:10:18 +0200
Committer: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Wed, 14 Aug 2013 17:14:50 +0200
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@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Kevin Hilman <khilman@xxxxxxxxxx>
---
kernel/sched/cputime.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 5f273b4..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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