Messages in this thread Patch in this message | | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH v2 1/8] preempt: Provide preempt_[dis|en]able_nested() | Date | Thu, 25 Aug 2022 18:41:24 +0200 |
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From: Thomas Gleixner <tglx@linutronix.de>
On PREEMPT_RT enabled kernels, spinlocks and rwlocks are neither disabling preemption nor interrupts. Though there are a few places which depend on the implicit preemption/interrupt disable of those locks, e.g. seqcount write sections, per CPU statistics updates etc.
To avoid sprinkling CONFIG_PREEMPT_RT conditionals all over the place, add preempt_disable_nested() and preempt_enable_nested() which should be descriptive enough.
Add a lockdep assertion for the !PREEMPT_RT case to catch callers which do not have preemption disabled.
Cc: Ben Segall <bsegall@google.com> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/linux/preempt.h | 42 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+)
diff --git a/include/linux/preempt.h b/include/linux/preempt.h index b4381f255a5ca..0df425bf9bd75 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -421,4 +421,46 @@ static inline void migrate_enable(void) { } #endif /* CONFIG_SMP */ +/** + * preempt_disable_nested - Disable preemption inside a normally preempt disabled section + * + * Use for code which requires preemption protection inside a critical + * section which has preemption disabled implicitly on non-PREEMPT_RT + * enabled kernels, by e.g.: + * - holding a spinlock/rwlock + * - soft interrupt context + * - regular interrupt handlers + * + * On PREEMPT_RT enabled kernels spinlock/rwlock held sections, soft + * interrupt context and regular interrupt handlers are preemptible and + * only prevent migration. preempt_disable_nested() ensures that preemption + * is disabled for cases which require CPU local serialization even on + * PREEMPT_RT. For non-PREEMPT_RT kernels this is a NOP. + * + * The use cases are code sequences which are not serialized by a + * particular lock instance, e.g.: + * - seqcount write side critical sections where the seqcount is not + * associated to a particular lock and therefore the automatic + * protection mechanism does not work. This prevents a live lock + * against a preempting high priority reader. + * - RMW per CPU variable updates like vmstat. + */ +/* Macro to avoid header recursion hell vs. lockdep */ +#define preempt_disable_nested() \ +do { \ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) \ + preempt_disable(); \ + else \ + lockdep_assert_preemption_disabled(); \ +} while (0) + +/** + * preempt_enable_nested - Undo the effect of preempt_disable_nested() + */ +static __always_inline void preempt_enable_nested(void) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); +} + #endif /* __LINUX_PREEMPT_H */ -- 2.37.2
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