rcu: Make rcu_barrier() less disruptive (b1420f1c) · Commits · 戴 / test

kernel/rcutree.c

+209 −86

Original line number	Diff line number	Diff line
		@@ -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 struct completion rcu_barrier_completion;

		/*
		* 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
		@@ -1311,95 +1320,133 @@ 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.
		* 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
		* operations that might block must be done later from the CPU_DEAD
		* notifier.
		*
		* Note that the outgoing CPU's bit has already been cleared in the
		* cpu_online_mask. This allows us to randomly pick a callback
		* destination from the bits set in that mask.
		* Send the specified CPU's RCU callbacks to the orphanage. The
		* specified CPU must be offline, and the caller must hold the
		* ->onofflock.
		*/
		static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
		static void
		rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
		struct rcu_node rnp, struct rcu_data rdp)
		{
		int i;
		unsigned long mask;
		int receive_cpu = cpumask_any(cpu_online_mask);
		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. */
		/*
		* Orphan the callbacks. First adjust the counts. This is safe
		* because ->onofflock excludes _rcu_barrier()'s adoption of
		* the callbacks, thus no memory barrier is required.
		*/
		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;
		}

		/*
		* 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;
		*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;
		}

		/*
		* Record a quiescent state for the dying CPU. This is safe
		* only because we have already cleared out the callbacks.
		* (Otherwise, the RCU core might try to schedule the invocation
		* of callbacks on this now-offline CPU, which would be bad.)
		* Adopt the RCU callbacks from the specified rcu_state structure's
		* orphanage. The caller must hold the ->onofflock.
		*/
		mask = rdp->grpmask; /* rnp->grplo is constant. */
		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;
		}
		}

		/*
		* Trace the fact that this CPU is going offline.
		*/
		static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
		{
		RCU_TRACE(unsigned long mask);
		RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
		RCU_TRACE(struct rcu_node *rnp = rdp->mynode);

		RCU_TRACE(mask = rdp->grpmask);
		trace_rcu_grace_period(rsp->name,
		rnp->gpnum + 1 - !!(rnp->qsmask & mask),
		"cpuofl");
		rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
		/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
		}

		/*
		* The CPU has been completely removed, and some other CPU is reporting
		* this fact from process context. Do the remainder of the cleanup.
		* this fact from process context. Do the remainder of the cleanup,
		* including orphaning the outgoing CPU's RCU callbacks, and also
		* adopting them, if there is no _rcu_barrier() instance running.
		* There can only be one CPU hotplug operation at a time, so no other
		* CPU can be attempting to update rcu_cpu_kthread_task.
		*/
		@@ -1409,17 +1456,21 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
		unsigned long mask;
		int need_report = 0;
		struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
		struct rcu_node rnp = rdp->mynode; / Outgoing CPU's rnp. */
		struct rcu_node rnp = rdp->mynode; / Outgoing CPU's rdp & rnp. */

		/* Adjust any no-longer-needed kthreads. */
		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);

		/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
		rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
		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 +1507,10 @@ 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 +1579,6 @@ 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 +1588,10 @@ 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 +1880,14 @@ __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,
		@@ -2169,11 +2226,10 @@ 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;

		/*
		* RCU callback function for _rcu_barrier(). If we are last, wake
		* up the task executing _rcu_barrier().
		*/
		static void rcu_barrier_callback(struct rcu_head *notused)
		{
		if (atomic_dec_and_test(&rcu_barrier_cpu_count))
		@@ -2203,27 +2259,94 @@ 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!!!
		*/
		init_completion(&rcu_barrier_completion);
		atomic_set(&rcu_barrier_cpu_count, 1);
		on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
		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();
		} else {
		preempt_enable();
		}
		}

		/*
		* 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);
		rsp->rcu_barrier_in_progress = NULL;
		raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
		atomic_inc(&rcu_barrier_cpu_count);
		smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */
		call_rcu_func(&rh, rcu_barrier_callback);

		/*
		* Now that we have an rcu_barrier_callback() callback on each
		* CPU, and thus each counted, remove the initial count.
		*/
		if (atomic_dec_and_test(&rcu_barrier_cpu_count))
		complete(&rcu_barrier_completion);

		/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
		wait_for_completion(&rcu_barrier_completion);

		/* Other rcu_barrier() invocations can now safely proceed. */
		mutex_unlock(&rcu_barrier_mutex);

		destroy_rcu_head_on_stack(&rh);
		}

		/**

kernel/rcutree.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -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 */

kernel/rcutree_trace.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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");

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