Messages in this thread | | | Date | Thu, 31 Jul 2014 09:58:52 -0700 | From | josh@joshtrip ... | Subject | Re: [PATCH v2 tip/core/rcu 03/10] rcu: Add synchronous grace-period waiting for RCU-tasks |
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On Wed, Jul 30, 2014 at 05:39:35PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > It turns out to be easier to add the synchronous grace-period waiting > functions to RCU-tasks than to work around their absense in rcutorture, > so this commit adds them. The key point is that the existence of > call_rcu_tasks() means that rcutorture needs an rcu_barrier_tasks(). > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
With rcu_barrier_tasks being a trivial wrapper, why not just let rcutorture call synchronize_rcu_tasks directly?
> include/linux/rcupdate.h | 2 ++ > kernel/rcu/update.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 57 insertions(+) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 3299ff98ad03..17c7e25c38be 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -216,6 +216,8 @@ void synchronize_sched(void); > * memory ordering guarantees. > */ > void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head)); > +void synchronize_rcu_tasks(void); > +void rcu_barrier_tasks(void); > > #ifdef CONFIG_PREEMPT_RCU > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > index b92268647a01..c8d304dc6d8a 100644 > --- a/kernel/rcu/update.c > +++ b/kernel/rcu/update.c > @@ -387,6 +387,61 @@ void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp)) > } > EXPORT_SYMBOL_GPL(call_rcu_tasks); > > +/** > + * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. > + * > + * Control will return to the caller some time after a full rcu-tasks > + * grace period has elapsed, in other words after all currently > + * executing rcu-tasks read-side critical sections have elapsed. These > + * read-side critical sections are delimited by calls to schedule(), > + * cond_resched_rcu_qs(), idle execution, userspace execution, calls > + * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). > + * > + * This is a very specialized primitive, intended only for a few uses in > + * tracing and other situations requiring manipulation of function > + * preambles and profiling hooks. The synchronize_rcu_tasks() function > + * is not (yet) intended for heavy use from multiple CPUs. > + * > + * Note that this guarantee implies further memory-ordering guarantees. > + * On systems with more than one CPU, when synchronize_rcu_tasks() returns, > + * each CPU is guaranteed to have executed a full memory barrier since the > + * end of its last RCU-tasks read-side critical section whose beginning > + * preceded the call to synchronize_rcu_tasks(). In addition, each CPU > + * having an RCU-tasks read-side critical section that extends beyond > + * the return from synchronize_rcu_tasks() is guaranteed to have executed > + * a full memory barrier after the beginning of synchronize_rcu_tasks() > + * and before the beginning of that RCU-tasks read-side critical section. > + * Note that these guarantees include CPUs that are offline, idle, or > + * executing in user mode, as well as CPUs that are executing in the kernel. > + * > + * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned > + * to its caller on CPU B, then both CPU A and CPU B are guaranteed > + * to have executed a full memory barrier during the execution of > + * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU > + * (but again only if the system has more than one CPU). > + */ > +void synchronize_rcu_tasks(void) > +{ > + /* Complain if the scheduler has not started. */ > + rcu_lockdep_assert(!rcu_scheduler_active, > + "synchronize_rcu_tasks called too soon"); > + > + /* Wait for the grace period. */ > + wait_rcu_gp(call_rcu_tasks); > +} > + > +/** > + * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. > + * > + * Although the current implementation is guaranteed to wait, it is not > + * obligated to, for example, if there are no pending callbacks. > + */ > +void rcu_barrier_tasks(void) > +{ > + /* There is only one callback queue, so this is easy. ;-) */ > + synchronize_rcu_tasks(); > +} > + > /* RCU-tasks kthread that detects grace periods and invokes callbacks. */ > static int __noreturn rcu_tasks_kthread(void *arg) > { > -- > 1.8.1.5 >
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