rcu: Move synchronize_sched_expedited() to rcutree.c
Now that TREE_RCU and TREE_PREEMPT_RCU no longer do anything different for the single-CPU case, there is no need for multiple definitions of synchronize_sched_expedited(). It is no longer in any sense a plug-in, so move it from kernel/rcutree_plugin.h to kernel/rcutree.c. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
Paul E. McKenney
Родитель
c0d6d01bff
Коммит
3d3b7db0a2
117
kernel/rcutree.c
117
kernel/rcutree.c
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@ -50,6 +50,8 @@
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#include <linux/wait.h>
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#include <linux/kthread.h>
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#include <linux/prefetch.h>
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#include <linux/delay.h>
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#include <linux/stop_machine.h>
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#include "rcutree.h"
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#include <trace/events/rcu.h>
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@ -1918,6 +1920,121 @@ void synchronize_rcu_bh(void)
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
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static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
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static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
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static int synchronize_sched_expedited_cpu_stop(void *data)
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{
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/*
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* There must be a full memory barrier on each affected CPU
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* between the time that try_stop_cpus() is called and the
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* time that it returns.
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*
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* In the current initial implementation of cpu_stop, the
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* above condition is already met when the control reaches
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* this point and the following smp_mb() is not strictly
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* necessary. Do smp_mb() anyway for documentation and
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* robustness against future implementation changes.
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*/
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smp_mb(); /* See above comment block. */
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return 0;
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}
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/*
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* Wait for an rcu-sched grace period to elapse, but use "big hammer"
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* approach to force grace period to end quickly. This consumes
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* significant time on all CPUs, and is thus not recommended for
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* any sort of common-case code.
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*
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* Note that it is illegal to call this function while holding any
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* lock that is acquired by a CPU-hotplug notifier. Failing to
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* observe this restriction will result in deadlock.
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*
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* This implementation can be thought of as an application of ticket
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* locking to RCU, with sync_sched_expedited_started and
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* sync_sched_expedited_done taking on the roles of the halves
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* of the ticket-lock word. Each task atomically increments
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* sync_sched_expedited_started upon entry, snapshotting the old value,
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* then attempts to stop all the CPUs. If this succeeds, then each
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* CPU will have executed a context switch, resulting in an RCU-sched
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* grace period. We are then done, so we use atomic_cmpxchg() to
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* update sync_sched_expedited_done to match our snapshot -- but
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* only if someone else has not already advanced past our snapshot.
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*
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* On the other hand, if try_stop_cpus() fails, we check the value
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* of sync_sched_expedited_done. If it has advanced past our
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* initial snapshot, then someone else must have forced a grace period
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* some time after we took our snapshot. In this case, our work is
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* done for us, and we can simply return. Otherwise, we try again,
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* but keep our initial snapshot for purposes of checking for someone
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* doing our work for us.
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*
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* If we fail too many times in a row, we fall back to synchronize_sched().
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*/
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void synchronize_sched_expedited(void)
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{
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int firstsnap, s, snap, trycount = 0;
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/* Note that atomic_inc_return() implies full memory barrier. */
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firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
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get_online_cpus();
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WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
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/*
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* Each pass through the following loop attempts to force a
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* context switch on each CPU.
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*/
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while (try_stop_cpus(cpu_online_mask,
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synchronize_sched_expedited_cpu_stop,
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NULL) == -EAGAIN) {
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put_online_cpus();
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/* No joy, try again later. Or just synchronize_sched(). */
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if (trycount++ < 10)
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udelay(trycount * num_online_cpus());
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else {
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synchronize_sched();
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return;
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}
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/* Check to see if someone else did our work for us. */
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s = atomic_read(&sync_sched_expedited_done);
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if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
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smp_mb(); /* ensure test happens before caller kfree */
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return;
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}
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/*
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* Refetching sync_sched_expedited_started allows later
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* callers to piggyback on our grace period. We subtract
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* 1 to get the same token that the last incrementer got.
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* We retry after they started, so our grace period works
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* for them, and they started after our first try, so their
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* grace period works for us.
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*/
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get_online_cpus();
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snap = atomic_read(&sync_sched_expedited_started);
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smp_mb(); /* ensure read is before try_stop_cpus(). */
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}
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/*
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* Everyone up to our most recent fetch is covered by our grace
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* period. Update the counter, but only if our work is still
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* relevant -- which it won't be if someone who started later
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* than we did beat us to the punch.
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*/
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do {
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s = atomic_read(&sync_sched_expedited_done);
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if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
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smp_mb(); /* ensure test happens before caller kfree */
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break;
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}
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} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
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put_online_cpus();
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}
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EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
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/*
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* Check to see if there is any immediate RCU-related work to be done
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* by the current CPU, for the specified type of RCU, returning 1 if so.
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@ -25,7 +25,6 @@
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*/
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#include <linux/delay.h>
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#include <linux/stop_machine.h>
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#define RCU_KTHREAD_PRIO 1
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@ -1888,121 +1887,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
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static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
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static int synchronize_sched_expedited_cpu_stop(void *data)
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{
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/*
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* There must be a full memory barrier on each affected CPU
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* between the time that try_stop_cpus() is called and the
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* time that it returns.
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*
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* In the current initial implementation of cpu_stop, the
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* above condition is already met when the control reaches
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* this point and the following smp_mb() is not strictly
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* necessary. Do smp_mb() anyway for documentation and
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* robustness against future implementation changes.
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*/
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smp_mb(); /* See above comment block. */
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return 0;
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}
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/*
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* Wait for an rcu-sched grace period to elapse, but use "big hammer"
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* approach to force grace period to end quickly. This consumes
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* significant time on all CPUs, and is thus not recommended for
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* any sort of common-case code.
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*
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* Note that it is illegal to call this function while holding any
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* lock that is acquired by a CPU-hotplug notifier. Failing to
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* observe this restriction will result in deadlock.
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*
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* This implementation can be thought of as an application of ticket
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* locking to RCU, with sync_sched_expedited_started and
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* sync_sched_expedited_done taking on the roles of the halves
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* of the ticket-lock word. Each task atomically increments
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* sync_sched_expedited_started upon entry, snapshotting the old value,
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* then attempts to stop all the CPUs. If this succeeds, then each
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* CPU will have executed a context switch, resulting in an RCU-sched
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* grace period. We are then done, so we use atomic_cmpxchg() to
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* update sync_sched_expedited_done to match our snapshot -- but
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* only if someone else has not already advanced past our snapshot.
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*
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* On the other hand, if try_stop_cpus() fails, we check the value
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* of sync_sched_expedited_done. If it has advanced past our
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* initial snapshot, then someone else must have forced a grace period
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* some time after we took our snapshot. In this case, our work is
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* done for us, and we can simply return. Otherwise, we try again,
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* but keep our initial snapshot for purposes of checking for someone
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* doing our work for us.
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*
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* If we fail too many times in a row, we fall back to synchronize_sched().
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*/
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void synchronize_sched_expedited(void)
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{
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int firstsnap, s, snap, trycount = 0;
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/* Note that atomic_inc_return() implies full memory barrier. */
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firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
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get_online_cpus();
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WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
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/*
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* Each pass through the following loop attempts to force a
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* context switch on each CPU.
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*/
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while (try_stop_cpus(cpu_online_mask,
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synchronize_sched_expedited_cpu_stop,
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NULL) == -EAGAIN) {
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put_online_cpus();
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/* No joy, try again later. Or just synchronize_sched(). */
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if (trycount++ < 10)
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udelay(trycount * num_online_cpus());
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else {
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synchronize_sched();
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return;
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}
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/* Check to see if someone else did our work for us. */
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s = atomic_read(&sync_sched_expedited_done);
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if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
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smp_mb(); /* ensure test happens before caller kfree */
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return;
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}
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/*
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* Refetching sync_sched_expedited_started allows later
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* callers to piggyback on our grace period. We subtract
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* 1 to get the same token that the last incrementer got.
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* We retry after they started, so our grace period works
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* for them, and they started after our first try, so their
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* grace period works for us.
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*/
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get_online_cpus();
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snap = atomic_read(&sync_sched_expedited_started);
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smp_mb(); /* ensure read is before try_stop_cpus(). */
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}
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/*
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* Everyone up to our most recent fetch is covered by our grace
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* period. Update the counter, but only if our work is still
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* relevant -- which it won't be if someone who started later
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* than we did beat us to the punch.
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*/
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do {
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s = atomic_read(&sync_sched_expedited_done);
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if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
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smp_mb(); /* ensure test happens before caller kfree */
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break;
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}
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} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
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put_online_cpus();
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}
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EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
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#if !defined(CONFIG_RCU_FAST_NO_HZ)
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/*
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