Commit e7d8842e authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

rcu: Apply results of code inspection of kernel/rcutree_plugin.h 



o Drop the calls to cpu_quiet() from the online/offline code.
  These are unnecessary, since force_quiescent_state() will
  clean up, and removing them simplifies the code a bit.

o Add a warning to check that we don't enqueue the same blocked
  task twice onto the ->blocked_tasks[] lists.

o Rework the phase computation in rcu_preempt_note_context_switch()
  to be more readable, as suggested by Josh Triplett.

o Disable irqs to close a race between the scheduling clock
  interrupt and rcu_preempt_note_context_switch() WRT the
  ->rcu_read_unlock_special field.

o Add comments to rnp->lock acquisition and release within
  rcu_read_unlock_special() noting that irqs are already
  disabled.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference: <12532926201851-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 28ecd580

kernel/rcutree.c

+5 −22
Original line number Diff line number Diff line
@@ -767,10 +767,10 @@ cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, 


/*

 * Record a quiescent state for the specified CPU, which must either be

 * the current CPU or an offline CPU.  The lastcomp argument is used to

 * make sure we are still in the grace period of interest.  We don't want

 * to end the current grace period based on quiescent states detected in

 * an earlier grace period!

 * the current CPU.  The lastcomp argument is used to make sure we are

 * still in the grace period of interest.  We don't want to end the current

 * grace period based on quiescent states detected in an earlier grace

 * period!

 */

static void

cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
@@ -805,7 +805,6 @@ cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp) 
		 * This GP can't end until cpu checks in, so all of our

		 * callbacks can be processed during the next GP.

		 */

		rdp = rsp->rda[smp_processor_id()];

		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];



		cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */
@@ -881,9 +880,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) 


	spin_unlock(&rsp->onofflock);		/* irqs remain disabled. */



	/* Being offline is a quiescent state, so go record it. */

	cpu_quiet(cpu, rsp, rdp, lastcomp);



	/*

	 * Move callbacks from the outgoing CPU to the running CPU.

	 * Note that the outgoing CPU is now quiscent, so it is now
@@ -1448,20 +1444,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable) 
		rnp = rnp->parent;

	} while (rnp != NULL && !(rnp->qsmaskinit & mask));



	spin_unlock(&rsp->onofflock);		/* irqs remain disabled. */



	/*

	 * A new grace period might start here.  If so, we will be part of

	 * it, and its gpnum will be greater than ours, so we will

	 * participate.  It is also possible for the gpnum to have been

	 * incremented before this function was called, and the bitmasks

	 * to not be filled out until now, in which case we will also

	 * participate due to our gpnum being behind.

	 */



	/* Since it is coming online, the CPU is in a quiescent state. */

	cpu_quiet(cpu, rsp, rdp, lastcomp);

	local_irq_restore(flags);

	spin_unlock_irqrestore(&rsp->onofflock, flags);

}



static void __cpuinit rcu_online_cpu(int cpu)

kernel/rcutree_plugin.h

+6 −4
Original line number Diff line number Diff line
@@ -117,9 +117,9 @@ static void rcu_preempt_note_context_switch(int cpu) 
		 * on line!

		 */

		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);

		phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);

		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));

		phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;

		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);

		smp_mb();  /* Ensure later ctxt swtch seen after above. */

		spin_unlock_irqrestore(&rnp->lock, flags);

	}
@@ -133,7 +133,9 @@ static void rcu_preempt_note_context_switch(int cpu) 
	 * means that we continue to block the current grace period.

	 */

	rcu_preempt_qs(cpu);

	local_irq_save(flags);

	t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;

	local_irq_restore(flags);

}



/*
@@ -189,10 +191,10 @@ static void rcu_read_unlock_special(struct task_struct *t) 
		 */

		for (;;) {

			rnp = t->rcu_blocked_node;

			spin_lock(&rnp->lock);

			spin_lock(&rnp->lock);  /* irqs already disabled. */

			if (rnp == t->rcu_blocked_node)

				break;

			spin_unlock(&rnp->lock);

			spin_unlock(&rnp->lock);  /* irqs remain disabled. */

		}

		empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);

		list_del_init(&t->rcu_node_entry);

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