Re: [PATCH 1/3] sched: Introduce is_pcpu_safe()
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2021-07-27 16:23:30
Also in:
linux-arm-kernel, lkml
On Wed, Jul 21, 2021 at 12:51:16PM +0100, Valentin Schneider wrote:
Some areas use preempt_disable() + preempt_enable() to safely access per-CPU data. The PREEMPT_RT folks have shown this can also be done by keeping preemption enabled and instead disabling migration (and acquiring a sleepable lock, if relevant). Introduce a helper which checks whether the current task can safely access per-CPU data, IOW if the task's context guarantees the accesses will target a single CPU. This accounts for preemption, CPU affinity, and migrate disable - note that the CPU affinity check also mandates the presence of PF_NO_SETAFFINITY, as otherwise userspace could concurrently render the upcoming per-CPU access(es) unsafe. Signed-off-by: Valentin Schneider <redacted>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
quoted hunk ↗ jump to hunk
--- include/linux/sched.h | 10 ++++++++++ 1 file changed, 10 insertions(+)diff --git a/include/linux/sched.h b/include/linux/sched.h index efdbdf654876..7ce2d5c1ad55 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h@@ -1707,6 +1707,16 @@ static inline bool is_percpu_thread(void) #endif } +/* Is the current task guaranteed not to be migrated elsewhere? */ +static inline bool is_pcpu_safe(void) +{ +#ifdef CONFIG_SMP + return !preemptible() || is_percpu_thread() || current->migration_disabled; +#else + return true; +#endif +} + /* Per-process atomic flags. */ #define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */ #define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */-- 2.25.1