rcu: Fix note_new_gpnum() uses of ->gpnum (9160306e) · Commits · 戴 / test

Impose a clear locking design on the note_new_gpnum() function's use of the ->gpnum counter. This is done by updating rdp->gpnum only from the corresponding leaf rcu_node structure's rnp->gpnum field, and even then only under the protection of that same rcu_node structure's ->lock field. Performance and scalability are maintained using a form of double-checked locking, and excessive spinning is avoided by use of the spin_trylock() function. The use of spin_trylock() is safe due to the fact that CPUs who fail to acquire this lock will try again later. The hierarchical nature of the rcu_node data structure limits contention (which could be limited further if need be using the RCU_FANOUT kernel parameter). Without this patch, obscure but quite possible races could result in a quiescent state that occurred during one grace period to be accounted to the following grace period, causing this following grace period to end prematurely. Not good! Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com 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 Cc: dhowells@redhat.com Cc: <stable@kernel.org> # .32.x LKML-Reference: <12571987492350-git-send-email-> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/rcutree.c

+27 −5

Original line number	Diff line number	Diff line
		@@ -540,13 +540,33 @@ static void check_cpu_stall(struct rcu_state rsp, struct rcu_data rdp)
		/*
		* Update CPU-local rcu_data state to record the newly noticed grace period.
		* This is used both when we started the grace period and when we notice
		* that someone else started the grace period.
		* that someone else started the grace period. The caller must hold the
		* ->lock of the leaf rcu_node structure corresponding to the current CPU,
		* and must have irqs disabled.
		*/
		static void note_new_gpnum(struct rcu_state rsp, struct rcu_data rdp)
		static void __note_new_gpnum(struct rcu_state rsp, struct rcu_node rnp, struct rcu_data *rdp)
		{
		if (rdp->gpnum != rnp->gpnum) {
		rdp->qs_pending = 1;
		rdp->passed_quiesc = 0;
		rdp->gpnum = rsp->gpnum;
		rdp->gpnum = rnp->gpnum;
		}
		}

		static void note_new_gpnum(struct rcu_state rsp, struct rcu_data rdp)
		{
		unsigned long flags;
		struct rcu_node *rnp;

		local_irq_save(flags);
		rnp = rdp->mynode;
		if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) \|\| /* outside lock. */
		!spin_trylock(&rnp->lock)) { /* irqs already off, retry later. */
		local_irq_restore(flags);
		return;
		}
		__note_new_gpnum(rsp, rnp, rdp);
		spin_unlock_irqrestore(&rnp->lock, flags);
		}

		/*
		@@ -637,6 +657,9 @@ rcu_start_gp_per_cpu(struct rcu_state rsp, struct rcu_node rnp, struct rcu_dat
		*/
		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
		rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

		/* Set state so that this CPU will detect the next quiescent state. */
		__note_new_gpnum(rsp, rnp, rdp);
		}

		/*
		@@ -664,7 +687,6 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
		rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
		record_gp_stall_check_time(rsp);
		dyntick_record_completed(rsp, rsp->completed - 1);
		note_new_gpnum(rsp, rdp);

		/* Special-case the common single-level case. */
		if (NUM_RCU_NODES == 1) {

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