linux-kernel - [PATCH v2 21/45] block: Use get/put_online_cpus

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Message-ID: <20130625202924.16593.95312.stgit@srivatsabhat.in.ibm.com>
Date:	Wed, 26 Jun 2013 01:59:24 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org, laijs@...fujitsu.com
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, sbw@....edu, fweisbec@...il.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	srivatsa.bhat@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v2 21/45] block: Use get/put_online_cpus_atomic() to prevent
 CPU offline

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 block/blk-softirq.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 467c8de..bbab3d3 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -58,6 +58,7 @@ static void trigger_softirq(void *data)
  */
 static int raise_blk_irq(int cpu, struct request *rq)
 {
+	get_online_cpus_atomic();
 	if (cpu_online(cpu)) {
 		struct call_single_data *data = &rq->csd;
 
@@ -66,8 +67,10 @@ static int raise_blk_irq(int cpu, struct request *rq)
 		data->flags = 0;
 
 		__smp_call_function_single(cpu, data, 0);
+		put_online_cpus_atomic();
 		return 0;
 	}
+	put_online_cpus_atomic();
 
 	return 1;
 }

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