| Message ID | 20210721115118.729943-2-valentin.schneider@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sched: migrate_disable() vs per-CPU access safety checks | expand |
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 <valentin.schneider@arm.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> > --- > 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 >
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 */
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 <valentin.schneider@arm.com> --- include/linux/sched.h | 10 ++++++++++ 1 file changed, 10 insertions(+)