From bde6c3aa993066acb0d6ce32ecabe03b9d5df92d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 1 Jul 2014 11:26:57 -0700 Subject: [PATCH] rcu: Provide cond_resched_rcu_qs() to force quiescent states in long loops RCU-tasks requires the occasional voluntary context switch from CPU-bound in-kernel tasks. In some cases, this requires instrumenting cond_resched(). However, there is some reluctance to countenance unconditionally instrumenting cond_resched() (see http://lwn.net/Articles/603252/), so this commit creates a separate cond_resched_rcu_qs() that may be used in place of cond_resched() in locations prone to long-duration in-kernel looping. This commit currently instruments only RCU-tasks. Future possibilities include also instrumenting RCU, RCU-bh, and RCU-sched in order to reduce IPI usage. Signed-off-by: Paul E. McKenney --- fs/file.c | 2 +- include/linux/rcupdate.h | 13 +++++++++++++ kernel/rcu/rcutorture.c | 4 ++-- kernel/rcu/tree.c | 12 ++++++------ kernel/rcu/tree_plugin.h | 2 +- mm/mlock.c | 2 +- 6 files changed, 24 insertions(+), 11 deletions(-) diff --git a/fs/file.c b/fs/file.c index 66923fe3176e..1cafc4c9275b 100644 --- a/fs/file.c +++ b/fs/file.c @@ -367,7 +367,7 @@ static struct fdtable *close_files(struct files_struct * files) struct file * file = xchg(&fdt->fd[i], NULL); if (file) { filp_close(file, files); - cond_resched(); + cond_resched_rcu_qs(); } } i++; diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 3432063f4c87..473350462d04 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -330,6 +330,19 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev, #define rcu_note_voluntary_context_switch(t) do { } while (0) #endif /* #else #ifdef CONFIG_TASKS_RCU */ +/** + * cond_resched_rcu_qs - Report potential quiescent states to RCU + * + * This macro resembles cond_resched(), except that it is defined to + * report potential quiescent states to RCU-tasks even if the cond_resched() + * machinery were to be shut off, as some advocate for PREEMPT kernels. + */ +#define cond_resched_rcu_qs() \ +do { \ + rcu_note_voluntary_context_switch(current); \ + cond_resched(); \ +} while (0) + #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) bool __rcu_is_watching(void); #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */ diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 948a7693748e..178716713e11 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -667,7 +667,7 @@ static int rcu_torture_boost(void *arg) } call_rcu_time = jiffies; } - cond_resched(); + cond_resched_rcu_qs(); stutter_wait("rcu_torture_boost"); if (torture_must_stop()) goto checkwait; @@ -1019,7 +1019,7 @@ rcu_torture_reader(void *arg) __this_cpu_inc(rcu_torture_batch[completed]); preempt_enable(); cur_ops->readunlock(idx); - cond_resched(); + cond_resched_rcu_qs(); stutter_wait("rcu_torture_reader"); } while (!torture_must_stop()); if (irqreader && cur_ops->irq_capable) { diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8ad91d1e317d..e23dad0661e2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1647,7 +1647,7 @@ static int rcu_gp_init(struct rcu_state *rsp) rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); raw_spin_unlock_irq(&rnp->lock); - cond_resched(); + cond_resched_rcu_qs(); } mutex_unlock(&rsp->onoff_mutex); @@ -1736,7 +1736,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) /* smp_mb() provided by prior unlock-lock pair. */ nocb += rcu_future_gp_cleanup(rsp, rnp); raw_spin_unlock_irq(&rnp->lock); - cond_resched(); + cond_resched_rcu_qs(); } rnp = rcu_get_root(rsp); raw_spin_lock_irq(&rnp->lock); @@ -1785,7 +1785,7 @@ static int __noreturn rcu_gp_kthread(void *arg) /* Locking provides needed memory barrier. */ if (rcu_gp_init(rsp)) break; - cond_resched(); + cond_resched_rcu_qs(); flush_signals(current); trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum), @@ -1828,10 +1828,10 @@ static int __noreturn rcu_gp_kthread(void *arg) trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum), TPS("fqsend")); - cond_resched(); + cond_resched_rcu_qs(); } else { /* Deal with stray signal. */ - cond_resched(); + cond_resched_rcu_qs(); flush_signals(current); trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum), @@ -2434,7 +2434,7 @@ static void force_qs_rnp(struct rcu_state *rsp, struct rcu_node *rnp; rcu_for_each_leaf_node(rsp, rnp) { - cond_resched(); + cond_resched_rcu_qs(); mask = 0; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a7997e272564..7672586d3920 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1848,7 +1848,7 @@ static int rcu_oom_notify(struct notifier_block *self, get_online_cpus(); for_each_online_cpu(cpu) { smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); - cond_resched(); + cond_resched_rcu_qs(); } put_online_cpus(); diff --git a/mm/mlock.c b/mm/mlock.c index ce84cb0b83ef..ab3150c26711 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -789,7 +789,7 @@ static int do_mlockall(int flags) /* Ignore errors */ mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); - cond_resched(); + cond_resched_rcu_qs(); } out: return 0;