From 4fe83223d4202247051abf360f60ee8f355ba3da Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 5 Oct 2011 11:59:38 -0700 Subject: rcu: Merge RCU-bh into RCU-preempt The Linux kernel has long RCU-bh read-side critical sections that intolerably increase scheduling latency under mainline's RCU-bh rules, which include RCU-bh read-side critical sections being non-preemptible. This patch therefore arranges for RCU-bh to be implemented in terms of RCU-preempt for CONFIG_PREEMPT_RT_FULL=y. This has the downside of defeating the purpose of RCU-bh, namely, handling the case where the system is subjected to a network-based denial-of-service attack that keeps at least one CPU doing full-time softirq processing. This issue will be fixed by a later commit. The current commit will need some work to make it appropriate for mainline use, for example, it needs to be extended to cover Tiny RCU. [ paulmck: Added a useful changelog ] Signed-off-by: Thomas Gleixner Signed-off-by: Paul E. McKenney Link: http://lkml.kernel.org/r/20111005185938.GA20403@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner --- include/linux/rcupdate.h | 25 +++++++++++++++++++++++++ include/linux/rcutree.h | 18 ++++++++++++++++-- 2 files changed, 41 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 23a500f70fcf..888d24ac66ba 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -101,6 +101,9 @@ extern void call_rcu(struct rcu_head *head, #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ +#ifdef CONFIG_PREEMPT_RT_FULL +#define call_rcu_bh call_rcu +#else /** * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. @@ -121,6 +124,7 @@ extern void call_rcu(struct rcu_head *head, */ extern void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *head)); +#endif /** * call_rcu_sched() - Queue an RCU for invocation after sched grace period. @@ -190,7 +194,13 @@ static inline int rcu_preempt_depth(void) /* Internal to kernel */ extern void rcu_sched_qs(int cpu); + +#ifndef CONFIG_PREEMPT_RT_FULL extern void rcu_bh_qs(int cpu); +#else +static inline void rcu_bh_qs(int cpu) { } +#endif + extern void rcu_check_callbacks(int cpu, int user); struct notifier_block; extern void rcu_idle_enter(void); @@ -331,7 +341,14 @@ static inline int rcu_read_lock_held(void) * rcu_read_lock_bh_held() is defined out of line to avoid #include-file * hell. */ +#ifdef CONFIG_PREEMPT_RT_FULL +static inline int rcu_read_lock_bh_held(void) +{ + return rcu_read_lock_held(); +} +#else extern int rcu_read_lock_bh_held(void); +#endif /** * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? @@ -780,10 +797,14 @@ static inline void rcu_read_unlock(void) static inline void rcu_read_lock_bh(void) { local_bh_disable(); +#ifdef CONFIG_PREEMPT_RT_FULL + rcu_read_lock(); +#else __acquire(RCU_BH); rcu_lock_acquire(&rcu_bh_lock_map); rcu_lockdep_assert(!rcu_is_cpu_idle(), "rcu_read_lock_bh() used illegally while idle"); +#endif } /* @@ -793,10 +814,14 @@ static inline void rcu_read_lock_bh(void) */ static inline void rcu_read_unlock_bh(void) { +#ifdef CONFIG_PREEMPT_RT_FULL + rcu_read_unlock(); +#else rcu_lockdep_assert(!rcu_is_cpu_idle(), "rcu_read_unlock_bh() used illegally while idle"); rcu_lock_release(&rcu_bh_lock_map); __release(RCU_BH); +#endif local_bh_enable(); } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index e8ee5dd0854c..5b2d03e18c3e 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -57,7 +57,11 @@ static inline void exit_rcu(void) #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ +#ifndef CONFIG_PREEMPT_RT_FULL extern void synchronize_rcu_bh(void); +#else +# define synchronize_rcu_bh() synchronize_rcu() +#endif extern void synchronize_sched_expedited(void); extern void synchronize_rcu_expedited(void); @@ -85,19 +89,29 @@ static inline void synchronize_rcu_bh_expedited(void) } extern void rcu_barrier(void); +#ifdef CONFIG_PREEMPT_RT_FULL +# define rcu_barrier_bh rcu_barrier +#else extern void rcu_barrier_bh(void); +#endif extern void rcu_barrier_sched(void); extern unsigned long rcutorture_testseq; extern unsigned long rcutorture_vernum; extern long rcu_batches_completed(void); -extern long rcu_batches_completed_bh(void); extern long rcu_batches_completed_sched(void); extern void rcu_force_quiescent_state(void); -extern void rcu_bh_force_quiescent_state(void); extern void rcu_sched_force_quiescent_state(void); +#ifndef CONFIG_PREEMPT_RT_FULL +extern void rcu_bh_force_quiescent_state(void); +extern long rcu_batches_completed_bh(void); +#else +# define rcu_bh_force_quiescent_state rcu_force_quiescent_state +# define rcu_batches_completed_bh rcu_batches_completed +#endif + /* A context switch is a grace period for RCU-sched and RCU-bh. */ static inline int rcu_blocking_is_gp(void) { -- cgit v1.2.3