diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2023-02-22 15:46:44 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2023-04-18 16:35:12 +0200 |
| commit | 620a30fa0bd14878891b22bf2261e6ed4587c2b4 (patch) | |
| tree | 9d193dac68bacb68e34c573819d7c570c96dbc6b /kernel/time/tick-sched.h | |
| parent | 07b65a800b6d5b6afbd6a91487b47038eac97c21 (diff) | |
| download | lwn-620a30fa0bd14878891b22bf2261e6ed4587c2b4.tar.gz lwn-620a30fa0bd14878891b22bf2261e6ed4587c2b4.zip | |
timers/nohz: Protect idle/iowait sleep time under seqcount
Reading idle/IO sleep time (eg: from /proc/stat) can race with idle exit
updates because the state machine handling the stats is not atomic and
requires a coherent read batch.
As a result reading the sleep time may report irrelevant or backward
values.
Fix this with protecting the simple state machine within a seqcount.
This is expected to be cheap enough not to add measurable performance
impact on the idle path.
Note this only fixes reader VS writer condition partitially. A race
remains that involves remote updates of the CPU iowait task counter. It
can hardly be fixed.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-4-frederic@kernel.org
Diffstat (limited to 'kernel/time/tick-sched.h')
| -rw-r--r-- | kernel/time/tick-sched.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h index c6663254d17d..5ed5a9d41d5a 100644 --- a/kernel/time/tick-sched.h +++ b/kernel/time/tick-sched.h @@ -75,6 +75,7 @@ struct tick_sched { ktime_t idle_waketime; /* Idle entry */ + seqcount_t idle_sleeptime_seq; ktime_t idle_entrytime; /* Tick stop */ |