Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 13/23] vtime: Fix racy cputime delta update | Date | Thu, 1 Aug 2013 02:31:30 +0200 |
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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> --- kernel/sched/cputime.c | 3 ++- 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); -- 1.7.5.4
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