Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH RFC 4/7] rcu: Move __rcu_read_lock() and __rcu_read_unlock() to per-CPU variables | Date | Sat, 14 Apr 2012 09:20:34 -0700 |
| |
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
This commit is another step towards inlinable __rcu_read_lock() and __rcu_read_unlock() functions for preemptible RCU. This keeps these two functions out of line, but switches them to use the per-CPU variables that are required to export their definitions without requiring that all RCU users include sched.h. These per-CPU variables are saved and restored at context-switch time.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- arch/um/drivers/mconsole_kern.c | 3 +- include/linux/init_task.h | 4 +- include/linux/rcupdate.h | 20 +++++++- include/linux/sched.h | 92 +++++++++++++++++++++++++++++++--- kernel/rcu.h | 4 ++ kernel/rcupdate.c | 54 ++++++++++++++++++-- kernel/rcutiny_plugin.h | 106 ++++++++------------------------------ kernel/rcutree_plugin.h | 85 ++++++++----------------------- kernel/sched/core.c | 3 +- 9 files changed, 209 insertions(+), 162 deletions(-)
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c index f69ff2d..a98693f 100644 --- a/arch/um/drivers/mconsole_kern.c +++ b/arch/um/drivers/mconsole_kern.c @@ -704,8 +704,9 @@ static void stack_proc(void *arg) struct task_struct *from = current, *to = arg; to->thread.saved_task = from; - rcu_switch_from(from); + rcu_switch_from(); switch_to(from, to, from); + rcu_switch_to(); } /* diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 9c66b1a..cdd8436 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -105,8 +105,8 @@ extern struct group_info init_groups; #endif #ifdef CONFIG_PREEMPT_RCU #define INIT_TASK_RCU_PREEMPT(tsk) \ - .rcu_read_lock_nesting = 0, \ - .rcu_read_unlock_special = 0, \ + .rcu_read_lock_nesting_save = 0, \ + .rcu_read_unlock_special_save = 0, \ .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \ INIT_TASK_RCU_TREE_PREEMPT() \ INIT_TASK_RCU_BOOST() diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5a94dcf..89f7e97 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -146,6 +146,9 @@ extern void synchronize_sched(void); DECLARE_PER_CPU(int, rcu_read_lock_nesting); DECLARE_PER_CPU(int, rcu_read_unlock_special); +#ifdef CONFIG_PROVE_RCU +DECLARE_PER_CPU(struct task_struct *, rcu_current_task); +#endif /* #ifdef CONFIG_PROVE_RCU */ extern void __rcu_read_lock(void); extern void __rcu_read_unlock(void); @@ -157,7 +160,22 @@ void synchronize_rcu(void); * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. */ -#define rcu_preempt_depth() (current->rcu_read_lock_nesting) +#define rcu_preempt_depth() (__this_cpu_read(rcu_read_lock_nesting)) + +/* + * Check for a running RCU reader on the current CPU. If used from + * TINY_PREEMPT_RCU, works globally, as there can be but one running + * RCU reader at a time in that case. ;-) + * + * Returns zero if there are no running readers. Returns a positive + * number if there is at least one reader within its RCU read-side + * critical section. Returns a negative number if an outermost reader + * is in the midst of exiting from its RCU read-side critical section + * + * This differs from rcu_preempt_depth() in throwing a build error + * if used from under !CONFIG_PREEMPT_RCU. + */ +#define rcu_preempt_running_reader() (__this_cpu_read(rcu_read_lock_nesting)) #else /* #ifdef CONFIG_PREEMPT_RCU */ diff --git a/include/linux/sched.h b/include/linux/sched.h index a749c9d..65e7023 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1275,8 +1275,8 @@ struct task_struct { cpumask_t cpus_allowed; #ifdef CONFIG_PREEMPT_RCU - int rcu_read_lock_nesting; - char rcu_read_unlock_special; + int rcu_read_lock_nesting_save; + char rcu_read_unlock_special_save; struct list_head rcu_node_entry; #endif /* #ifdef CONFIG_PREEMPT_RCU */ #ifdef CONFIG_TREE_PREEMPT_RCU @@ -1868,8 +1868,8 @@ extern void task_clear_jobctl_pending(struct task_struct *task, static inline void rcu_copy_process(struct task_struct *p) { - p->rcu_read_lock_nesting = 0; - p->rcu_read_unlock_special = 0; + p->rcu_read_lock_nesting_save = 0; + p->rcu_read_unlock_special_save = 0; #ifdef CONFIG_TREE_PREEMPT_RCU p->rcu_blocked_node = NULL; #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ @@ -1879,10 +1879,84 @@ static inline void rcu_copy_process(struct task_struct *p) INIT_LIST_HEAD(&p->rcu_node_entry); } -static inline void rcu_switch_from(struct task_struct *prev) +/* + * Let preemptible RCU know about a switch away from a task. + * + * First, if there is an ongoing RCU read-side critical section, invoke + * rcu_preempt_note_context_switch() to enqueue the task. + * + * We need to save both of the __rcu_read_lock() / __rcu_read_unlock() + * per-CPU variables in either case so that they can be correctly restored + * when this task resumes. + * + * Subsequent RCU read-side critical sections can occur either in the + * architecture switch_to() function or in interrupt handlers. Both + * cases rely on the fact that if rcu_read_unlock_special is zero, then + * rcu_read_lock_nesting must also be zero. Thus, the only way that such + * a critical section can enter rcu_read_unlock_special() is if: + * + * 1. The per-CPU rcu_read_lock_nesting variable was zero, and: + * 2. The critical section took a scheduling-clock interrupt, + * setting the RCU_READ_UNLOCK_NEED_QS bit. + * + * This is harmless. It will cause the CPU to register a quiescent state, + * which is OK because the CPU really is in a quiescent state and if the + * outgoing task was not in a quiescent state, it has already been queued. + * In particular, RCU_READ_UNLOCK_BLOCKED cannot be set because preemption + * is disabled. + * + * If rcu_read_lock_nesting is non-zero, then any subsequent RCU read-side + * critical section will act as if nested, thus refusing to enter the + * rcu_read_unlock_special() function in the first place. + * + * The caller must have disabled preemption. + */ +static inline void rcu_switch_from(void) { - if (prev->rcu_read_lock_nesting != 0) + struct task_struct *t = current; + + if (__this_cpu_read(rcu_read_lock_nesting) != 0) rcu_preempt_note_context_switch(); + t->rcu_read_lock_nesting_save = __this_cpu_read(rcu_read_lock_nesting); + t->rcu_read_unlock_special_save = + __this_cpu_read(rcu_read_unlock_special); +#ifdef CONFIG_PROVE_RCU + barrier(); + /* Idle tasks can have NULL rcu_current_task at boot time. */ + BUG_ON(__this_cpu_read(rcu_current_task) != t && + __this_cpu_read(rcu_current_task) != NULL); + __this_cpu_write(rcu_current_task, NULL); +#endif /* #ifdef CONFIG_PROVE_RCU */ +} + +/* + * Let preemptible RCU know about a switch to a task. + * + * This requires some care in order to preserve the invariant + * mentioned above. First zero rcu_read_unlock_special, then + * restore the value of rcu_read_lock_nesting, and only then restore + * rcu_read_unlock_special_save. (Yes, there is a check in + * rcu_read_unlock_special() that is supposed to prevent interrupt + * handlers from getting to far into that function, but this check + * are unavoidably heuristic in nature.) + * + * The caller must have disabled preemption. + */ +static inline void rcu_switch_to(void) +{ + struct task_struct *t = current; + + __this_cpu_write(rcu_read_unlock_special, 0); + barrier(); /* Ensure ordering to maintain invariant. */ + __this_cpu_write(rcu_read_lock_nesting, t->rcu_read_lock_nesting_save); + barrier(); /* Ensure ordering to maintain invariant. */ + __this_cpu_write(rcu_read_unlock_special, + t->rcu_read_unlock_special_save); +#ifdef CONFIG_PROVE_RCU + barrier(); + BUG_ON(__this_cpu_read(rcu_current_task) != NULL); + __this_cpu_write(rcu_current_task, t); +#endif /* #ifdef CONFIG_PROVE_RCU */ } #else @@ -1891,7 +1965,11 @@ static inline void rcu_copy_process(struct task_struct *p) { } -static inline void rcu_switch_from(struct task_struct *prev) +static inline void rcu_switch_from(void) +{ +} + +static inline void rcu_switch_to(void) { } diff --git a/kernel/rcu.h b/kernel/rcu.h index 8ba99cd..6243d8d 100644 --- a/kernel/rcu.h +++ b/kernel/rcu.h @@ -109,4 +109,8 @@ static inline bool __rcu_reclaim(char *rn, struct rcu_head *head) } } +#ifdef CONFIG_PREEMPT_RCU +extern void rcu_read_unlock_do_special(void); +#endif /* #ifdef CONFIG_PREEMPT_RCU */ + #endif /* __LINUX_RCU_H */ diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 1acf0da..f77a5fc 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -54,6 +54,54 @@ #ifdef CONFIG_PREEMPT_RCU DEFINE_PER_CPU(int, rcu_read_lock_nesting); DEFINE_PER_CPU(int, rcu_read_unlock_special); +#ifdef CONFIG_PROVE_RCU +DEFINE_PER_CPU(struct task_struct *, rcu_current_task); +#endif /* #ifdef CONFIG_PROVE_RCU */ + +/* + * Preemptible-RCU implementation for rcu_read_lock(). Just increment + * the per-CPU rcu_read_lock_nesting: Shared state and per-task state will + * be updated if we block. + */ +void __rcu_read_lock(void) +{ + __this_cpu_inc(rcu_read_lock_nesting); + barrier(); /* Keep code within RCU read-side critical section. */ +} +EXPORT_SYMBOL_GPL(__rcu_read_lock); + +/* + * Tree-preemptible RCU implementation for rcu_read_unlock(). + * Decrement rcu_read_lock_nesting. If the result is zero (outermost + * rcu_read_unlock()) and rcu_read_unlock_special is non-zero, then + * invoke rcu_read_unlock_do_special() to clean up after a context switch + * in an RCU read-side critical section and other special cases. + * Set rcu_read_lock_nesting to a large negative value during cleanup + * in order to ensure that if rcu_read_unlock_special is non-zero, then + * rcu_read_lock_nesting is also non-zero. + */ +void __rcu_read_unlock(void) +{ + if (__this_cpu_read(rcu_read_lock_nesting) != 1) + __this_cpu_dec(rcu_read_lock_nesting); + else { + barrier(); /* critical section before exit code. */ + __this_cpu_write(rcu_read_lock_nesting, INT_MIN); + barrier(); /* assign before ->rcu_read_unlock_special load */ + if (unlikely(__this_cpu_read(rcu_read_unlock_special))) + rcu_read_unlock_do_special(); + barrier(); /* ->rcu_read_unlock_special load before assign */ + __this_cpu_write(rcu_read_lock_nesting, 0); + } +#ifdef CONFIG_PROVE_LOCKING + { + int rln = __this_cpu_read(rcu_read_lock_nesting); + + WARN_ON_ONCE(rln < 0 && rln > INT_MIN / 2); + } +#endif /* #ifdef CONFIG_PROVE_LOCKING */ +} +EXPORT_SYMBOL_GPL(__rcu_read_unlock); /* * Check for a task exiting while in a preemptible-RCU read-side @@ -63,13 +111,11 @@ DEFINE_PER_CPU(int, rcu_read_unlock_special); */ void exit_rcu(void) { - struct task_struct *t = current; - if (likely(list_empty(¤t->rcu_node_entry))) return; - t->rcu_read_lock_nesting = 1; + __this_cpu_write(rcu_read_lock_nesting, 1); barrier(); - t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; + __this_cpu_write(rcu_read_unlock_special, RCU_READ_UNLOCK_BLOCKED); __rcu_read_unlock(); } diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 66a542a..6b416af 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -132,7 +132,6 @@ static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { RCU_TRACE(.rcb.name = "rcu_preempt") }; -static void rcu_read_unlock_do_special(struct task_struct *t); static int rcu_preempted_readers_exp(void); static void rcu_report_exp_done(void); @@ -145,25 +144,6 @@ static int rcu_cpu_blocking_cur_gp(void) } /* - * Check for a running RCU reader. Because there is only one CPU, - * there can be but one running RCU reader at a time. ;-) - * - * Returns zero if there are no running readers. Returns a positive - * number if there is at least one reader within its RCU read-side - * critical section. Returns a negative number if an outermost reader - * is in the midst of exiting from its RCU read-side critical section - * - * Returns zero if there are no running readers. Returns a positive - * number if there is at least one reader within its RCU read-side - * critical section. Returns a negative number if an outermost reader - * is in the midst of exiting from its RCU read-side critical section. - */ -static int rcu_preempt_running_reader(void) -{ - return current->rcu_read_lock_nesting; -} - -/* * Check for preempted RCU readers blocking any grace period. * If the caller needs a reliable answer, it must disable hard irqs. */ @@ -395,7 +375,7 @@ static void rcu_preempt_boost_start_gp(void) * * Unlike the other rcu_*_qs() functions, callers to this function * must disable irqs in order to protect the assignment to - * ->rcu_read_unlock_special. + * rcu_read_unlock_special. * * Because this is a single-CPU implementation, the only way a grace * period can end is if the CPU is in a quiescent state. The reason is @@ -412,7 +392,7 @@ static void rcu_preempt_cpu_qs(void) { /* Record both CPU and task as having responded to current GP. */ rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; - current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; + __get_cpu_var(rcu_read_unlock_special) &= ~RCU_READ_UNLOCK_NEED_QS; /* If there is no GP then there is nothing more to do. */ if (!rcu_preempt_gp_in_progress()) @@ -486,10 +466,12 @@ void rcu_preempt_note_context_switch(void) local_irq_save(flags); /* must exclude scheduler_tick(). */ if (rcu_preempt_running_reader() > 0 && - (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { + (__this_cpu_read(rcu_read_unlock_special) & + RCU_READ_UNLOCK_BLOCKED) == 0) { /* Possibly blocking in an RCU read-side critical section. */ - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; + __get_cpu_var(rcu_read_unlock_special) |= + RCU_READ_UNLOCK_BLOCKED; /* * If this CPU has already checked in, then this task @@ -505,12 +487,12 @@ void rcu_preempt_note_context_switch(void) if (rcu_cpu_blocking_cur_gp()) rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; } else if (rcu_preempt_running_reader() < 0 && - t->rcu_read_unlock_special) { + __this_cpu_read(rcu_read_unlock_special)) { /* * Complete exit from RCU read-side critical section on * behalf of preempted instance of __rcu_read_unlock(). */ - rcu_read_unlock_do_special(t); + rcu_read_unlock_do_special(); } /* @@ -527,23 +509,11 @@ void rcu_preempt_note_context_switch(void) } /* - * Tiny-preemptible RCU implementation for rcu_read_lock(). - * Just increment ->rcu_read_lock_nesting, shared state will be updated - * if we block. - */ -void __rcu_read_lock(void) -{ - current->rcu_read_lock_nesting++; - barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ -} -EXPORT_SYMBOL_GPL(__rcu_read_lock); - -/* * Handle special cases during rcu_read_unlock(), such as needing to * notify RCU core processing or task having blocked during the RCU * read-side critical section. */ -static noinline void rcu_read_unlock_do_special(struct task_struct *t) +void rcu_read_unlock_do_special(void) { int empty; int empty_exp; @@ -567,7 +537,7 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) * If RCU core is waiting for this CPU to exit critical section, * let it know that we have done so. */ - special = t->rcu_read_unlock_special; + special = __this_cpu_read(rcu_read_unlock_special); if (special & RCU_READ_UNLOCK_NEED_QS) rcu_preempt_cpu_qs(); @@ -579,7 +549,10 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) /* Clean up if blocked during RCU read-side critical section. */ if (special & RCU_READ_UNLOCK_BLOCKED) { - t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; + struct task_struct *t = current; + + __get_cpu_var(rcu_read_unlock_special) &= + ~RCU_READ_UNLOCK_BLOCKED; /* * Remove this task from the ->blkd_tasks list and adjust @@ -614,49 +587,17 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) */ if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) rcu_report_exp_done(); - } #ifdef CONFIG_RCU_BOOST - /* Unboost self if was boosted. */ - if (t->rcu_boost_mutex != NULL) { - rbmp = t->rcu_boost_mutex; - t->rcu_boost_mutex = NULL; - rt_mutex_unlock(rbmp); - } + /* Unboost self if was boosted. */ + if (t->rcu_boost_mutex != NULL) { + rbmp = t->rcu_boost_mutex; + t->rcu_boost_mutex = NULL; + rt_mutex_unlock(rbmp); + } #endif /* #ifdef CONFIG_RCU_BOOST */ - local_irq_restore(flags); -} - -/* - * Tiny-preemptible RCU implementation for rcu_read_unlock(). - * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost - * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then - * invoke rcu_read_unlock_do_special() to clean up after a context switch - * in an RCU read-side critical section and other special cases. - */ -void __rcu_read_unlock(void) -{ - struct task_struct *t = current; - - barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ - if (t->rcu_read_lock_nesting != 1) - --t->rcu_read_lock_nesting; - else { - t->rcu_read_lock_nesting = INT_MIN; - barrier(); /* assign before ->rcu_read_unlock_special load */ - if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) - rcu_read_unlock_do_special(t); - barrier(); /* ->rcu_read_unlock_special load before assign */ - t->rcu_read_lock_nesting = 0; - } -#ifdef CONFIG_PROVE_LOCKING - { - int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); - - WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); } -#endif /* #ifdef CONFIG_PROVE_LOCKING */ + local_irq_restore(flags); } -EXPORT_SYMBOL_GPL(__rcu_read_unlock); /* * Check for a quiescent state from the current CPU. When a task blocks, @@ -667,8 +608,6 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock); */ static void rcu_preempt_check_callbacks(void) { - struct task_struct *t = current; - if (rcu_preempt_gp_in_progress() && (!rcu_preempt_running_reader() || !rcu_cpu_blocking_cur_gp())) @@ -679,7 +618,8 @@ static void rcu_preempt_check_callbacks(void) if (rcu_preempt_gp_in_progress() && rcu_cpu_blocking_cur_gp() && rcu_preempt_running_reader() > 0) - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; + __get_cpu_var(rcu_read_unlock_special) |= + RCU_READ_UNLOCK_NEED_QS; } /* diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 76a1ba9..20be289 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -78,7 +78,6 @@ struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); static struct rcu_state *rcu_state = &rcu_preempt_state; -static void rcu_read_unlock_do_special(struct task_struct *t); static int rcu_preempted_readers_exp(struct rcu_node *rnp); /* @@ -126,7 +125,7 @@ EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); * * Unlike the other rcu_*_qs() functions, callers to this function * must disable irqs in order to protect the assignment to - * ->rcu_read_unlock_special. + * rcu_read_unlock_special. */ static void rcu_preempt_qs(int cpu) { @@ -137,7 +136,7 @@ static void rcu_preempt_qs(int cpu) if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; - current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; + __get_cpu_var(rcu_read_unlock_special) &= ~RCU_READ_UNLOCK_NEED_QS; } /* @@ -160,14 +159,16 @@ void rcu_preempt_note_context_switch(void) struct rcu_data *rdp; struct rcu_node *rnp; - if (t->rcu_read_lock_nesting > 0 && - (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { + if (__this_cpu_read(rcu_read_lock_nesting) > 0 && + (__this_cpu_read(rcu_read_unlock_special) & + RCU_READ_UNLOCK_BLOCKED) == 0) { /* Possibly blocking in an RCU read-side critical section. */ rdp = __this_cpu_ptr(rcu_preempt_state.rda); rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; + __get_cpu_var(rcu_read_unlock_special) |= + RCU_READ_UNLOCK_BLOCKED; t->rcu_blocked_node = rnp; /* @@ -208,14 +209,14 @@ void rcu_preempt_note_context_switch(void) ? rnp->gpnum : rnp->gpnum + 1); raw_spin_unlock_irqrestore(&rnp->lock, flags); - } else if (t->rcu_read_lock_nesting < 0 && - t->rcu_read_unlock_special) { + } else if (__this_cpu_read(rcu_read_lock_nesting) < 0 && + __this_cpu_read(rcu_read_unlock_special)) { /* - * Complete exit from RCU read-side critical section on + * Finish the exit from RCU read-side critical section on * behalf of preempted instance of __rcu_read_unlock(). */ - rcu_read_unlock_do_special(t); + rcu_read_unlock_do_special(); } /* @@ -233,18 +234,6 @@ void rcu_preempt_note_context_switch(void) } /* - * Tree-preemptible RCU implementation for rcu_read_lock(). - * Just increment ->rcu_read_lock_nesting, shared state will be updated - * if we block. - */ -void __rcu_read_lock(void) -{ - current->rcu_read_lock_nesting++; - barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ -} -EXPORT_SYMBOL_GPL(__rcu_read_lock); - -/* * Check for preempted RCU readers blocking the current grace period * for the specified rcu_node structure. If the caller needs a reliable * answer, it must hold the rcu_node's ->lock. @@ -310,7 +299,7 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t, * notify RCU core processing or task having blocked during the RCU * read-side critical section. */ -static noinline void rcu_read_unlock_do_special(struct task_struct *t) +void rcu_read_unlock_do_special(void) { int empty; int empty_exp; @@ -333,7 +322,7 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) * If RCU core is waiting for this CPU to exit critical section, * let it know that we have done so. */ - special = t->rcu_read_unlock_special; + special = __this_cpu_read(rcu_read_unlock_special); if (special & RCU_READ_UNLOCK_NEED_QS) { rcu_preempt_qs(smp_processor_id()); } @@ -346,7 +335,10 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) /* Clean up if blocked during RCU read-side critical section. */ if (special & RCU_READ_UNLOCK_BLOCKED) { - t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; + struct task_struct *t = current; + + __get_cpu_var(rcu_read_unlock_special) &= + ~RCU_READ_UNLOCK_BLOCKED; /* * Remove this task from the list it blocked on. The @@ -418,38 +410,6 @@ static noinline void rcu_read_unlock_do_special(struct task_struct *t) } } -/* - * Tree-preemptible RCU implementation for rcu_read_unlock(). - * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost - * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then - * invoke rcu_read_unlock_do_special() to clean up after a context switch - * in an RCU read-side critical section and other special cases. - */ -void __rcu_read_unlock(void) -{ - struct task_struct *t = current; - - if (t->rcu_read_lock_nesting != 1) - --t->rcu_read_lock_nesting; - else { - barrier(); /* critical section before exit code. */ - t->rcu_read_lock_nesting = INT_MIN; - barrier(); /* assign before ->rcu_read_unlock_special load */ - if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) - rcu_read_unlock_do_special(t); - barrier(); /* ->rcu_read_unlock_special load before assign */ - t->rcu_read_lock_nesting = 0; - } -#ifdef CONFIG_PROVE_LOCKING - { - int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); - - WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); - } -#endif /* #ifdef CONFIG_PROVE_LOCKING */ -} -EXPORT_SYMBOL_GPL(__rcu_read_unlock); - #ifdef CONFIG_RCU_CPU_STALL_VERBOSE /* @@ -666,15 +626,14 @@ static void rcu_preempt_cleanup_dead_cpu(int cpu) */ static void rcu_preempt_check_callbacks(int cpu) { - struct task_struct *t = current; - - if (t->rcu_read_lock_nesting == 0) { + if (__this_cpu_read(rcu_read_lock_nesting) == 0) { rcu_preempt_qs(cpu); return; } - if (t->rcu_read_lock_nesting > 0 && - per_cpu(rcu_preempt_data, cpu).qs_pending) - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; + if (__this_cpu_read(rcu_read_lock_nesting) > 0 && + __get_cpu_var(rcu_preempt_data).qs_pending) + __get_cpu_var(rcu_read_unlock_special) |= + RCU_READ_UNLOCK_NEED_QS; } /* diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 10689da..9f10b76 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2051,8 +2051,9 @@ context_switch(struct rq *rq, struct task_struct *prev, #endif /* Here we just switch the register state and the stack. */ - rcu_switch_from(prev); + rcu_switch_from(); switch_to(prev, next, prev); + rcu_switch_to(); barrier(); /* -- 1.7.8
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