linux-kernel - [PATCH v5 22/45] infiniband: ehca: Use get/put_online_cpus

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Date:	Tue, 22 Jan 2013 13:09:13 +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
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, rjw@...k.pl, sbw@....edu,
	fweisbec@...il.com, linux@....linux.org.uk,
	nikunj@...ux.vnet.ibm.com, srivatsa.bhat@...ux.vnet.ibm.com,
	linux-pm@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v5 22/45] infiniband: ehca: 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 preempt_disable() or local_irq_disable() 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: Roland Dreier <roland@...nel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 drivers/infiniband/hw/ehca/ehca_irq.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c
index 8615d7c..d61936c 100644
--- a/drivers/infiniband/hw/ehca/ehca_irq.c
+++ b/drivers/infiniband/hw/ehca/ehca_irq.c
@@ -43,6 +43,7 @@
 
 #include <linux/slab.h>
 #include <linux/smpboot.h>
+#include <linux/cpu.h>
 
 #include "ehca_classes.h"
 #include "ehca_irq.h"
@@ -653,6 +654,9 @@ void ehca_tasklet_eq(unsigned long data)
 	ehca_process_eq((struct ehca_shca*)data, 1);
 }
 
+/*
+ * Must be called under get_online_cpus_atomic() and put_online_cpus_atomic().
+ */
 static int find_next_online_cpu(struct ehca_comp_pool *pool)
 {
 	int cpu;
@@ -703,6 +707,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
 	int cq_jobs;
 	unsigned long flags;
 
+	get_online_cpus_atomic();
 	cpu_id = find_next_online_cpu(pool);
 	BUG_ON(!cpu_online(cpu_id));
 
@@ -720,6 +725,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
 		BUG_ON(!cct || !thread);
 	}
 	__queue_comp_task(__cq, cct, thread);
+	put_online_cpus_atomic();
 }
 
 static void run_comp_task(struct ehca_cpu_comp_task *cct)
@@ -759,6 +765,7 @@ static void comp_task_park(unsigned int cpu)
 	list_splice_init(&cct->cq_list, &list);
 	spin_unlock_irq(&cct->task_lock);
 
+	get_online_cpus_atomic();
 	cpu = find_next_online_cpu(pool);
 	target = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
 	thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu);
@@ -768,6 +775,7 @@ static void comp_task_park(unsigned int cpu)
 		__queue_comp_task(cq, target, thread);
 	}
 	spin_unlock_irq(&target->task_lock);
+	put_online_cpus_atomic();
 }
 
 static void comp_task_stop(unsigned int cpu, bool online)

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