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Message-ID: <20120315182159.GJ2381@linux.vnet.ibm.com>
Date: Thu, 15 Mar 2012 11:21:59 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com,
mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, josh@...htriplett.org, niv@...ibm.com,
tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
Valdis.Kletnieks@...edu, dhowells@...hat.com,
eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
patches@...aro.org
Subject: Re: [PATCH RFC] rcu: Make rcu_barrier() less disruptive
On Thu, Mar 15, 2012 at 01:45:27PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > The rcu_barrier() primitive interrupts each and every CPU, registering
> > a callback on every CPU. Once all of these callbacks have been invoked,
> > rcu_barrier() knows that every callback that was registered before
> > the call to rcu_barrier() has also been invoked.
> >
> > However, there is no point in registering a callback on a CPU that
> > currently has no callbacks, most especially if that CPU is in a
> > deep idle state. This commit therefore makes rcu_barrier() avoid
> > interrupting CPUs that have no callbacks. Doing this requires reworking
> > the handling of orphaned callbacks, otherwise callbacks could slip through
> > rcu_barrier()'s net by being orphaned from a CPU that rcu_barrier() had
> > not yet interrupted to a CPU that rcu_barrier() had already interrupted.
> > This reworking was needed anyway to take a first step towards weaning
> > RCU from the CPU_DYING notifier's use of stop_cpu().
>
> Quoting Documentation/RCU/rcubarrier.txt:
>
> "We instead need the rcu_barrier() primitive. This primitive is similar
> to synchronize_rcu(), but instead of waiting solely for a grace
> period to elapse, it also waits for all outstanding RCU callbacks to
> complete. Pseudo-code using rcu_barrier() is as follows:"
>
> The patch you propose seems like a good approach to make rcu_barrier
> less disruptive, but everyone need to be aware that rcu_barrier() would
> quit having the side-effect of doing the equivalent of
> "synchronize_rcu()" from now on: within this new approach, in the case
> where there are no pending callbacks, rcu_barrier() could, AFAIU, return
> without waiting for the current grace period to complete.
>
> Any use of rcu_barrier() that would assume that a synchronize_rcu() is
> implicit with the rcu_barrier() execution would be a bug anyway, but
> those might only show up after this patch is applied. I would therefore
> recommend to audit all rcu_barrier() users to ensure none is expecting
> rcu_barrier to act as a synchronize_rcu before pushing this change.
Good catch!
I am going to chicken out and explicitly wait for a grace period if there
were no callbacks. Having rcu_barrier() very rarely be a quick no-op does
sound like a standing invitation for subtle non-reproducible bugs. ;-)
Thanx, Paul
> Thanks,
>
> Mathieu
>
> >
> > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index 403306b..8269656 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -75,6 +75,8 @@ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
> > .gpnum = -300, \
> > .completed = -300, \
> > .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.onofflock), \
> > + .orphan_nxttail = &structname##_state.orphan_nxtlist, \
> > + .orphan_donetail = &structname##_state.orphan_donelist, \
> > .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.fqslock), \
> > .n_force_qs = 0, \
> > .n_force_qs_ngp = 0, \
> > @@ -145,6 +147,13 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
> > unsigned long rcutorture_testseq;
> > unsigned long rcutorture_vernum;
> >
> > +/* State information for rcu_barrier() and friends. */
> > +
> > +static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
> > +static atomic_t rcu_barrier_cpu_count;
> > +static DEFINE_MUTEX(rcu_barrier_mutex);
> > +static DECLARE_WAIT_QUEUE_HEAD(rcu_barrier_wq);
> > +
> > /*
> > * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
> > * permit this function to be invoked without holding the root rcu_node
> > @@ -1311,7 +1320,60 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
> > #ifdef CONFIG_HOTPLUG_CPU
> >
> > /*
> > - * Move a dying CPU's RCU callbacks to online CPU's callback list.
> > + * Adopt the RCU callbacks from the specified rcu_state structure's
> > + * orphanage. The caller must hold the ->onofflock.
> > + */
> > +static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
> > +{
> > + int i;
> > + struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
> > +
> > + /*
> > + * If there is an rcu_barrier() operation in progress, then
> > + * only the task doing that operation is permitted to adopt
> > + * callbacks. To do otherwise breaks rcu_barrier() and friends
> > + * by causing them to fail to wait for the callbacks in the
> > + * orphanage.
> > + */
> > + if (rsp->rcu_barrier_in_progress &&
> > + rsp->rcu_barrier_in_progress != current)
> > + return;
> > +
> > + /* Do the accounting first. */
> > + rdp->qlen_lazy += rsp->qlen_lazy;
> > + rdp->qlen += rsp->qlen;
> > + rdp->n_cbs_adopted += rsp->qlen;
> > + rsp->qlen_lazy = 0;
> > + rsp->qlen = 0;
> > +
> > + /*
> > + * We do not need a memory barrier here because the only way we
> > + * can get here if there is an rcu_barrier() in flight is if
> > + * we are the task doing the rcu_barrier().
> > + */
> > +
> > + /* First adopt the ready-to-invoke callbacks. */
> > + if (rsp->orphan_donelist != NULL) {
> > + *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
> > + *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
> > + for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
> > + if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
> > + rdp->nxttail[i] = rsp->orphan_donetail;
> > + rsp->orphan_donelist = NULL;
> > + rsp->orphan_donetail = &rsp->orphan_donelist;
> > + }
> > +
> > + /* And then adopt the callbacks that still need a grace period. */
> > + if (rsp->orphan_nxtlist != NULL) {
> > + *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
> > + rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
> > + rsp->orphan_nxtlist = NULL;
> > + rsp->orphan_nxttail = &rsp->orphan_nxtlist;
> > + }
> > +}
> > +
> > +/*
> > + * Move a dying CPU's RCU callbacks to the rcu_state structure's orphanage.
> > * Also record a quiescent state for this CPU for the current grace period.
> > * Synchronization and interrupt disabling are not required because
> > * this function executes in stop_machine() context. Therefore, cleanup
> > @@ -1325,64 +1387,67 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
> > static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
> > {
> > int i;
> > + unsigned long flags;
> > unsigned long mask;
> > - int receive_cpu = cpumask_any(cpu_online_mask);
> > + bool orphaned = 0;
> > struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
> > - struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
> > RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */
> >
> > - /* First, adjust the counts. */
> > + /* Move the callbacks to the orphanage under ->onofflock protection. */
> > + raw_spin_lock_irqsave(&rsp->onofflock, flags);
> > +
> > + /* First adjust the counts. */
> > if (rdp->nxtlist != NULL) {
> > - receive_rdp->qlen_lazy += rdp->qlen_lazy;
> > - receive_rdp->qlen += rdp->qlen;
> > + rsp->qlen_lazy += rdp->qlen_lazy;
> > + rsp->qlen += rdp->qlen;
> > + rdp->n_cbs_orphaned += rdp->qlen;
> > rdp->qlen_lazy = 0;
> > rdp->qlen = 0;
> > + orphaned = 1;
> > }
> >
> > /*
> > - * Next, move ready-to-invoke callbacks to be invoked on some
> > - * other CPU. These will not be required to pass through another
> > - * grace period: They are done, regardless of CPU.
> > + * Next, move those callbacks still needing a grace period to
> > + * the orphanage, where some other CPU will pick them up.
> > + * Some of the callbacks might have gone partway through a grace
> > + * period, but that is too bad. They get to start over because we
> > + * cannot assume that grace periods are synchronized across CPUs.
> > + * We don't bother updating the ->nxttail[] array yet, instead
> > + * we just reset the whole thing later on.
> > */
> > - if (rdp->nxtlist != NULL &&
> > - rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) {
> > - struct rcu_head *oldhead;
> > - struct rcu_head **oldtail;
> > - struct rcu_head **newtail;
> > -
> > - oldhead = rdp->nxtlist;
> > - oldtail = receive_rdp->nxttail[RCU_DONE_TAIL];
> > - rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
> > - *rdp->nxttail[RCU_DONE_TAIL] = *oldtail;
> > - *receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead;
> > - newtail = rdp->nxttail[RCU_DONE_TAIL];
> > - for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) {
> > - if (receive_rdp->nxttail[i] == oldtail)
> > - receive_rdp->nxttail[i] = newtail;
> > - if (rdp->nxttail[i] == newtail)
> > - rdp->nxttail[i] = &rdp->nxtlist;
> > - }
> > + if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
> > + *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
> > + rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
> > + *rdp->nxttail[RCU_DONE_TAIL] = NULL;
> > }
> >
> > /*
> > - * Finally, put the rest of the callbacks at the end of the list.
> > - * The ones that made it partway through get to start over: We
> > - * cannot assume that grace periods are synchronized across CPUs.
> > - * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
> > - * this does not seem compelling. Not yet, anyway.)
> > + * Then move the ready-to-invoke callbacks to the orphanage,
> > + * where some other CPU will pick them up. These will not be
> > + * required to pass though another grace period: They are done.
> > */
> > if (rdp->nxtlist != NULL) {
> > - *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
> > - receive_rdp->nxttail[RCU_NEXT_TAIL] =
> > - rdp->nxttail[RCU_NEXT_TAIL];
> > - receive_rdp->n_cbs_adopted += rdp->qlen;
> > - rdp->n_cbs_orphaned += rdp->qlen;
> > -
> > - rdp->nxtlist = NULL;
> > - for (i = 0; i < RCU_NEXT_SIZE; i++)
> > - rdp->nxttail[i] = &rdp->nxtlist;
> > + *rsp->orphan_donetail = rdp->nxtlist;
> > + rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
> > }
> >
> > + /* Finally, initialize the rcu_data structure's list to empty. */
> > + rdp->nxtlist = NULL;
> > + for (i = 0; i < RCU_NEXT_SIZE; i++)
> > + rdp->nxttail[i] = &rdp->nxtlist;
> > +
> > + /*
> > + * Wait up the rcu_barrier() task if there is one and if we
> > + * actually sent anything to the orphanage. Except that we
> > + * must delay the wakeup until ->onofflock is released to
> > + * avoid deadlock.
> > + */
> > + if (!rsp->rcu_barrier_in_progress)
> > + orphaned = 0;
> > + raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> > + if (orphaned)
> > + wake_up(&rcu_barrier_wq);
> > +
> > /*
> > * Record a quiescent state for the dying CPU. This is safe
> > * only because we have already cleared out the callbacks.
> > @@ -1415,11 +1480,14 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
> > rcu_stop_cpu_kthread(cpu);
> > rcu_node_kthread_setaffinity(rnp, -1);
> >
> > - /* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */
> > + /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
> >
> > /* Exclude any attempts to start a new grace period. */
> > raw_spin_lock_irqsave(&rsp->onofflock, flags);
> >
> > + /* Collect the dead CPU's callbacks. */
> > + rcu_adopt_orphan_cbs(rsp);
> > +
> > /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
> > mask = rdp->grpmask; /* rnp->grplo is constant. */
> > do {
> > @@ -1456,6 +1524,10 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
> >
> > #else /* #ifdef CONFIG_HOTPLUG_CPU */
> >
> > +static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
> > +{
> > +}
> > +
> > static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
> > {
> > }
> > @@ -1524,9 +1596,6 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
> > rcu_is_callbacks_kthread());
> >
> > /* Update count, and requeue any remaining callbacks. */
> > - rdp->qlen_lazy -= count_lazy;
> > - rdp->qlen -= count;
> > - rdp->n_cbs_invoked += count;
> > if (list != NULL) {
> > *tail = rdp->nxtlist;
> > rdp->nxtlist = list;
> > @@ -1536,6 +1605,10 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
> > else
> > break;
> > }
> > + smp_mb(); /* List handling before counting for rcu_barrier(). */
> > + rdp->qlen_lazy -= count_lazy;
> > + rdp->qlen -= count;
> > + rdp->n_cbs_invoked += count;
> >
> > /* Reinstate batch limit if we have worked down the excess. */
> > if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
> > @@ -1824,13 +1897,14 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
> > rdp = this_cpu_ptr(rsp->rda);
> >
> > /* Add the callback to our list. */
> > - *rdp->nxttail[RCU_NEXT_TAIL] = head;
> > - rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
> > rdp->qlen++;
> > if (lazy)
> > rdp->qlen_lazy++;
> > else
> > rcu_idle_count_callbacks_posted();
> > + smp_mb(); /* Count before adding callback for rcu_barrier(). */
> > + *rdp->nxttail[RCU_NEXT_TAIL] = head;
> > + rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
> >
> > if (__is_kfree_rcu_offset((unsigned long)func))
> > trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
> > @@ -2169,15 +2243,10 @@ static int rcu_cpu_has_callbacks(int cpu)
> > rcu_preempt_cpu_has_callbacks(cpu);
> > }
> >
> > -static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
> > -static atomic_t rcu_barrier_cpu_count;
> > -static DEFINE_MUTEX(rcu_barrier_mutex);
> > -static struct completion rcu_barrier_completion;
> > -
> > static void rcu_barrier_callback(struct rcu_head *notused)
> > {
> > if (atomic_dec_and_test(&rcu_barrier_cpu_count))
> > - complete(&rcu_barrier_completion);
> > + wake_up(&rcu_barrier_wq);
> > }
> >
> > /*
> > @@ -2203,27 +2272,121 @@ static void _rcu_barrier(struct rcu_state *rsp,
> > void (*call_rcu_func)(struct rcu_head *head,
> > void (*func)(struct rcu_head *head)))
> > {
> > - BUG_ON(in_interrupt());
> > + int cpu;
> > + unsigned long flags;
> > + struct rcu_data *rdp;
> > + struct rcu_head rh;
> > +
> > + init_rcu_head_on_stack(&rh);
> > +
> > /* Take mutex to serialize concurrent rcu_barrier() requests. */
> > mutex_lock(&rcu_barrier_mutex);
> > - init_completion(&rcu_barrier_completion);
> > +
> > + smp_mb(); /* Prevent any prior operations from leaking in. */
> > +
> > /*
> > - * Initialize rcu_barrier_cpu_count to 1, then invoke
> > - * rcu_barrier_func() on each CPU, so that each CPU also has
> > - * incremented rcu_barrier_cpu_count. Only then is it safe to
> > - * decrement rcu_barrier_cpu_count -- otherwise the first CPU
> > - * might complete its grace period before all of the other CPUs
> > - * did their increment, causing this function to return too
> > - * early. Note that on_each_cpu() disables irqs, which prevents
> > - * any CPUs from coming online or going offline until each online
> > - * CPU has queued its RCU-barrier callback.
> > + * Initialize the count to one rather than to zero in order to
> > + * avoid a too-soon return to zero in case of a short grace period
> > + * (or preemption of this task). Also flag this task as doing
> > + * an rcu_barrier(). This will prevent anyone else from adopting
> > + * orphaned callbacks, which could cause otherwise failure if a
> > + * CPU went offline and quickly came back online. To see this,
> > + * consider the following sequence of events:
> > + *
> > + * 1. We cause CPU 0 to post an rcu_barrier_callback() callback.
> > + * 2. CPU 1 goes offline, orphaning its callbacks.
> > + * 3. CPU 0 adopts CPU 1's orphaned callbacks.
> > + * 4. CPU 1 comes back online.
> > + * 5. We cause CPU 1 to post an rcu_barrier_callback() callback.
> > + * 6. Both rcu_barrier_callback() callbacks are invoked, awakening
> > + * us -- but before CPU 1's orphaned callbacks are invoked!!!
> > */
> > atomic_set(&rcu_barrier_cpu_count, 1);
> > - on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
> > - if (atomic_dec_and_test(&rcu_barrier_cpu_count))
> > - complete(&rcu_barrier_completion);
> > - wait_for_completion(&rcu_barrier_completion);
> > + raw_spin_lock_irqsave(&rsp->onofflock, flags);
> > + rsp->rcu_barrier_in_progress = current;
> > + raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> > +
> > + /*
> > + * Force every CPU with callbacks to register a new callback
> > + * that will tell us when all the preceding callbacks have
> > + * been invoked. If an offline CPU has callbacks, wait for
> > + * it to either come back online or to finish orphaning those
> > + * callbacks.
> > + */
> > + for_each_possible_cpu(cpu) {
> > + preempt_disable();
> > + rdp = per_cpu_ptr(rsp->rda, cpu);
> > + if (cpu_is_offline(cpu)) {
> > + preempt_enable();
> > + while (cpu_is_offline(cpu) &&
> > + ACCESS_ONCE(rdp->qlen))
> > + schedule_timeout_interruptible(1);
> > + } else if (ACCESS_ONCE(rdp->qlen)) {
> > + smp_call_function_single(cpu, rcu_barrier_func,
> > + (void *)call_rcu_func, 1);
> > + preempt_enable();
> > + }
> > + }
> > +
> > + /*
> > + * Force any ongoing CPU-hotplug operations to complete,
> > + * so that any callbacks from the outgoing CPUs are now in
> > + * the orphanage.
> > + */
> > + cpu_maps_update_begin();
> > + cpu_maps_update_done();
> > +
> > + /*
> > + * Now that all online CPUs have rcu_barrier_callback() callbacks
> > + * posted, we can adopt all of the orphaned callbacks and place
> > + * an rcu_barrier_callback() callback after them. When that is done,
> > + * we are guaranteed to have an rcu_barrier_callback() callback
> > + * following every callback that could possibly have been
> > + * registered before _rcu_barrier() was called.
> > + */
> > + raw_spin_lock_irqsave(&rsp->onofflock, flags);
> > + rcu_adopt_orphan_cbs(rsp);
> > + atomic_inc(&rcu_barrier_cpu_count);
> > + call_rcu_func(&rh, rcu_barrier_callback);
> > + raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> > +
> > + /*
> > + * Now that we have an rcu_barrier_callback() callback on each
> > + * CPU, and thus each counted, remove the initial count.
> > + */
> > + atomic_dec(&rcu_barrier_cpu_count);
> > + smp_mb__after_atomic_dec();
> > +
> > + /*
> > + * Loop waiting for all rcu_barrier_callback() callbacks to be
> > + * invoked. Adopt any orphaned callbacks in the meantime, just
> > + * in case one of the rcu_barrier_callback() callbacks is orphaned.
> > + */
> > + while (atomic_read(&rcu_barrier_cpu_count) > 0) {
> > + wait_event(rcu_barrier_wq,
> > + atomic_read(&rcu_barrier_cpu_count) == 0 ||
> > + ACCESS_ONCE(rsp->qlen));
> > + if (ACCESS_ONCE(rsp->qlen)) {
> > + raw_spin_lock_irqsave(&rsp->onofflock, flags);
> > + rcu_adopt_orphan_cbs(rsp);
> > + raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> > + }
> > + }
> > +
> > + /*
> > + * Done, so let others adopt orphaned callbacks. But avoid
> > + * indefinite postponement of any additional orphans by adopting
> > + * one more time.
> > + */
> > + raw_spin_lock_irqsave(&rsp->onofflock, flags);
> > + rcu_adopt_orphan_cbs(rsp);
> > + rsp->rcu_barrier_in_progress = NULL;
> > + raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> > +
> > + /* Other rcu_barrier() invocations can now safely proceed. */
> > mutex_unlock(&rcu_barrier_mutex);
> > +
> > + destroy_rcu_head_on_stack(&rh);
> > }
> >
> > /**
> > diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> > index 36ca28e..1e49c56 100644
> > --- a/kernel/rcutree.h
> > +++ b/kernel/rcutree.h
> > @@ -371,6 +371,17 @@ struct rcu_state {
> >
> > raw_spinlock_t onofflock; /* exclude on/offline and */
> > /* starting new GP. */
> > + struct rcu_head *orphan_nxtlist; /* Orphaned callbacks that */
> > + /* need a grace period. */
> > + struct rcu_head **orphan_nxttail; /* Tail of above. */
> > + struct rcu_head *orphan_donelist; /* Orphaned callbacks that */
> > + /* are ready to invoke. */
> > + struct rcu_head **orphan_donetail; /* Tail of above. */
> > + long qlen_lazy; /* Number of lazy callbacks. */
> > + long qlen; /* Total number of callbacks. */
> > + struct task_struct *rcu_barrier_in_progress;
> > + /* Task doing rcu_barrier(), */
> > + /* or NULL if no barrier. */
> > raw_spinlock_t fqslock; /* Only one task forcing */
> > /* quiescent states. */
> > unsigned long jiffies_force_qs; /* Time at which to invoke */
> > diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
> > index ed459ed..d4bc16d 100644
> > --- a/kernel/rcutree_trace.c
> > +++ b/kernel/rcutree_trace.c
> > @@ -271,13 +271,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
> >
> > gpnum = rsp->gpnum;
> > seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x "
> > - "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu\n",
> > + "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
> > rsp->completed, gpnum, rsp->fqs_state,
> > (long)(rsp->jiffies_force_qs - jiffies),
> > (int)(jiffies & 0xffff),
> > rsp->n_force_qs, rsp->n_force_qs_ngp,
> > rsp->n_force_qs - rsp->n_force_qs_ngp,
> > - rsp->n_force_qs_lh);
> > + rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen);
> > for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) {
> > if (rnp->level != level) {
> > seq_puts(m, "\n");
> >
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>
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