4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [ Upstream commit 66630058e56b26b3a9cf2625e250a8c592dd0207 ] Code which solely needs to prevent migration of a task uses preempt_disable()/enable() pairs. This is the only reliable way to do so as setting the task affinity to a single CPU can be undone by a setaffinity operation from a different task/process. RT provides a seperate migrate_disable/enable() mechanism which does not disable preemption to achieve the semantic requirements of a (almost) fully preemptible kernel. As it is unclear from looking at a given code path whether the intention is to disable preemption or migration, introduce migrate_disable/enable() inline functions which can be used to annotate code which merely needs to disable migration. Map them to preempt_disable/enable() for now. The RT substitution will be provided later. Code which is annotated that way documents that it has no requirement to protect against reentrancy of a preempting task. Either this is not required at all or the call sites are already serialized by other means. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Ben Segall <bsegall@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/878slclv1u.fsf@xxxxxxxxxxxxxxxxxxxxxxx Stable-dep-of: 36c75ce3bd29 ("nd_btt: Make BTT lanes preemptible") Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- include/linux/preempt.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/include/linux/preempt.h b/include/linux/preempt.h index c01813c3fbe93..abeec72b4d359 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -325,4 +325,34 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, #endif +/** + * migrate_disable - Prevent migration of the current task + * + * Maps to preempt_disable() which also disables preemption. Use + * migrate_disable() to annotate that the intent is to prevent migration, + * but not necessarily preemption. + * + * Can be invoked nested like preempt_disable() and needs the corresponding + * number of migrate_enable() invocations. + */ +static __always_inline void migrate_disable(void) +{ + preempt_disable(); +} + +/** + * migrate_enable - Allow migration of the current task + * + * Counterpart to migrate_disable(). + * + * As migrate_disable() can be invoked nested, only the outermost invocation + * reenables migration. + * + * Currently mapped to preempt_enable(). + */ +static __always_inline void migrate_enable(void) +{ + preempt_enable(); +} + #endif /* __LINUX_PREEMPT_H */ -- 2.42.0
