Subject: rcu: Merge RCU-bh into RCU-preempt Date: Wed, 5 Oct 2011 11:59:38 -0700 From: Thomas Gleixner Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.14/older/patches-4.14.15-rt13.tar.xz 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 | 23 +++++++++++++++++++++++ include/linux/rcutree.h | 8 ++++++++ kernel/rcu/rcu.h | 14 +++++++++++--- kernel/rcu/rcutorture.c | 7 +++++++ kernel/rcu/tree.c | 24 ++++++++++++++++++++++++ kernel/rcu/tree.h | 2 ++ kernel/rcu/update.c | 2 ++ 7 files changed, 77 insertions(+), 3 deletions(-) --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -56,7 +56,11 @@ void call_rcu(struct rcu_head *head, rcu #define call_rcu call_rcu_sched #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ +#ifdef CONFIG_PREEMPT_RT_FULL +#define call_rcu_bh call_rcu +#else void call_rcu_bh(struct rcu_head *head, rcu_callback_t func); +#endif void call_rcu_sched(struct rcu_head *head, rcu_callback_t func); void synchronize_sched(void); void rcu_barrier_tasks(void); @@ -113,7 +117,11 @@ static inline int rcu_preempt_depth(void void rcu_init(void); extern int rcu_scheduler_active __read_mostly; void rcu_sched_qs(void); +#ifdef CONFIG_PREEMPT_RT_FULL +static inline void rcu_bh_qs(void) { } +#else void rcu_bh_qs(void); +#endif void rcu_check_callbacks(int user); void rcu_report_dead(unsigned int cpu); void rcu_cpu_starting(unsigned int cpu); @@ -263,7 +271,14 @@ extern struct lockdep_map rcu_sched_lock extern struct lockdep_map rcu_callback_map; int debug_lockdep_rcu_enabled(void); int rcu_read_lock_held(void); +#ifdef CONFIG_PREEMPT_RT_FULL +static inline int rcu_read_lock_bh_held(void) +{ + return rcu_read_lock_held(); +} +#else int rcu_read_lock_bh_held(void); +#endif int rcu_read_lock_sched_held(void); #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ @@ -667,10 +682,14 @@ 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_WARN(!rcu_is_watching(), "rcu_read_lock_bh() used illegally while idle"); +#endif } /* @@ -680,10 +699,14 @@ 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_WARN(!rcu_is_watching(), "rcu_read_unlock_bh() used illegally while idle"); rcu_lock_release(&rcu_bh_lock_map); __release(RCU_BH); +#endif local_bh_enable(); } --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -44,7 +44,11 @@ static inline void rcu_virt_note_context rcu_note_context_switch(false); } +#ifdef CONFIG_PREEMPT_RT_FULL +# define synchronize_rcu_bh synchronize_rcu +#else void synchronize_rcu_bh(void); +#endif void synchronize_sched_expedited(void); void synchronize_rcu_expedited(void); @@ -72,7 +76,11 @@ static inline void synchronize_rcu_bh_ex } void rcu_barrier(void); +#ifdef CONFIG_PREEMPT_RT_FULL +# define rcu_barrier_bh rcu_barrier +#else void rcu_barrier_bh(void); +#endif void rcu_barrier_sched(void); unsigned long get_state_synchronize_rcu(void); void cond_synchronize_rcu(unsigned long oldstate); --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -462,18 +462,26 @@ static inline void show_rcu_gp_kthreads( extern unsigned long rcutorture_testseq; extern unsigned long rcutorture_vernum; unsigned long rcu_batches_started(void); -unsigned long rcu_batches_started_bh(void); unsigned long rcu_batches_started_sched(void); unsigned long rcu_batches_completed(void); -unsigned long rcu_batches_completed_bh(void); unsigned long rcu_batches_completed_sched(void); unsigned long rcu_exp_batches_completed(void); unsigned long rcu_exp_batches_completed_sched(void); unsigned long srcu_batches_completed(struct srcu_struct *sp); void show_rcu_gp_kthreads(void); void rcu_force_quiescent_state(void); -void rcu_bh_force_quiescent_state(void); void rcu_sched_force_quiescent_state(void); + +#ifndef CONFIG_PREEMPT_RT_FULL +void rcu_bh_force_quiescent_state(void); +unsigned long rcu_batches_started_bh(void); +unsigned 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 +# define rcu_batches_started_bh rcu_batches_completed +#endif + #endif /* #else #ifdef CONFIG_TINY_RCU */ #ifdef CONFIG_RCU_NOCB_CPU --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -417,6 +417,7 @@ static struct rcu_torture_ops rcu_ops = .name = "rcu" }; +#ifndef CONFIG_PREEMPT_RT_FULL /* * Definitions for rcu_bh torture testing. */ @@ -456,6 +457,12 @@ static struct rcu_torture_ops rcu_bh_ops .name = "rcu_bh" }; +#else +static struct rcu_torture_ops rcu_bh_ops = { + .ttype = INVALID_RCU_FLAVOR, +}; +#endif + /* * Don't even think about trying any of these in real life!!! * The names includes "busted", and they really means it! --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -243,6 +243,7 @@ void rcu_sched_qs(void) this_cpu_ptr(&rcu_sched_data), true); } +#ifndef CONFIG_PREEMPT_RT_FULL void rcu_bh_qs(void) { RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!"); @@ -253,6 +254,7 @@ void rcu_bh_qs(void) __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false); } } +#endif /* * Steal a bit from the bottom of ->dynticks for idle entry/exit @@ -564,11 +566,13 @@ EXPORT_SYMBOL_GPL(rcu_batches_started_sc /* * Return the number of RCU BH batches started thus far for debug & stats. */ +#ifndef CONFIG_PREEMPT_RT_FULL unsigned long rcu_batches_started_bh(void) { return rcu_bh_state.gpnum; } EXPORT_SYMBOL_GPL(rcu_batches_started_bh); +#endif /* * Return the number of RCU batches completed thus far for debug & stats. @@ -588,6 +592,7 @@ unsigned long rcu_batches_completed_sche } EXPORT_SYMBOL_GPL(rcu_batches_completed_sched); +#ifndef CONFIG_PREEMPT_RT_FULL /* * Return the number of RCU BH batches completed thus far for debug & stats. */ @@ -596,6 +601,7 @@ unsigned long rcu_batches_completed_bh(v return rcu_bh_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); +#endif /* * Return the number of RCU expedited batches completed thus far for @@ -619,6 +625,7 @@ unsigned long rcu_exp_batches_completed_ } EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched); +#ifndef CONFIG_PREEMPT_RT_FULL /* * Force a quiescent state. */ @@ -637,6 +644,13 @@ void rcu_bh_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); +#else +void rcu_force_quiescent_state(void) +{ +} +EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); +#endif + /* * Force a quiescent state for RCU-sched. */ @@ -687,9 +701,11 @@ void rcutorture_get_gp_data(enum rcutort case RCU_FLAVOR: rsp = rcu_state_p; break; +#ifndef CONFIG_PREEMPT_RT_FULL case RCU_BH_FLAVOR: rsp = &rcu_bh_state; break; +#endif case RCU_SCHED_FLAVOR: rsp = &rcu_sched_state; break; @@ -3113,6 +3129,7 @@ void call_rcu_sched(struct rcu_head *hea } EXPORT_SYMBOL_GPL(call_rcu_sched); +#ifndef CONFIG_PREEMPT_RT_FULL /** * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. @@ -3140,6 +3157,7 @@ void call_rcu_bh(struct rcu_head *head, __call_rcu(head, func, &rcu_bh_state, -1, 0); } EXPORT_SYMBOL_GPL(call_rcu_bh); +#endif /* * Queue an RCU callback for lazy invocation after a grace period. @@ -3225,6 +3243,7 @@ void synchronize_sched(void) } EXPORT_SYMBOL_GPL(synchronize_sched); +#ifndef CONFIG_PREEMPT_RT_FULL /** * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. * @@ -3251,6 +3270,7 @@ void synchronize_rcu_bh(void) wait_rcu_gp(call_rcu_bh); } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); +#endif /** * get_state_synchronize_rcu - Snapshot current RCU state @@ -3601,6 +3621,7 @@ static void _rcu_barrier(struct rcu_stat mutex_unlock(&rsp->barrier_mutex); } +#ifndef CONFIG_PREEMPT_RT_FULL /** * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. */ @@ -3609,6 +3630,7 @@ void rcu_barrier_bh(void) _rcu_barrier(&rcu_bh_state); } EXPORT_SYMBOL_GPL(rcu_barrier_bh); +#endif /** * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. @@ -4184,7 +4206,9 @@ void __init rcu_init(void) rcu_bootup_announce(); rcu_init_geometry(); +#ifndef CONFIG_PREEMPT_RT_FULL rcu_init_one(&rcu_bh_state); +#endif rcu_init_one(&rcu_sched_state); if (dump_tree) rcu_dump_rcu_node_tree(&rcu_sched_state); --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -427,7 +427,9 @@ extern struct list_head rcu_struct_flavo */ extern struct rcu_state rcu_sched_state; +#ifndef CONFIG_PREEMPT_RT_FULL extern struct rcu_state rcu_bh_state; +#endif #ifdef CONFIG_PREEMPT_RCU extern struct rcu_state rcu_preempt_state; --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -333,6 +333,7 @@ int rcu_read_lock_held(void) } EXPORT_SYMBOL_GPL(rcu_read_lock_held); +#ifndef CONFIG_PREEMPT_RT_FULL /** * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? * @@ -359,6 +360,7 @@ int rcu_read_lock_bh_held(void) return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); +#endif #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */