linux-kernel - [PATCH tip/core/rcu 31/45] torture: Notice if an all-zero cpumask is passed inside a critical section

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Message-Id: <1398731133-18925-31-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Mon, 28 Apr 2014 17:25:19 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	oleg@...hat.com, sbw@....edu,
	Iulia Manda <iulia.manda21@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 31/45] torture: Notice if an all-zero cpumask is passed inside a critical section

From: Iulia Manda <iulia.manda21@...il.com>

In torture_shuffle_tasks function, the check if an all-zero mask can
be passed to set_cpus_allowed_ptr() is redundant after clearing the
shuffle_idle_cpu bit. If the mask had more than one bit set, after
clearing a bit it has at least one bit set. If the mask had only
one bit set, a check is made at the beginning, where the function
returns, as there is no need to shuffle only one cpu.

Also, this code is executed inside a critical section, delimited by
get_online_cpus(), and put_online_cpus(), preventing CPUs from leaving between
the check of num_online_cpus and the calls to set_cpus_allowed_ptr() function.

Signed-off-by: Iulia Manda <iulia.manda21@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/torture.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/torture.c b/kernel/torture.c
index bd768effba9a..c1d57e83e8fe 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -335,13 +335,8 @@ static void torture_shuffle_tasks(void)
 	shuffle_idle_cpu = cpumask_next(shuffle_idle_cpu, shuffle_tmp_mask);
 	if (shuffle_idle_cpu >= nr_cpu_ids)
 		shuffle_idle_cpu = -1;
-	if (shuffle_idle_cpu != -1) {
+	else
 		cpumask_clear_cpu(shuffle_idle_cpu, shuffle_tmp_mask);
-		if (cpumask_empty(shuffle_tmp_mask)) {
-			put_online_cpus();
-			return;
-		}
-	}
 
 	mutex_lock(&shuffle_task_mutex);
 	list_for_each_entry(stp, &shuffle_task_list, st_l)
-- 
1.8.1.5

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