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SubjectRe: [PATCH] sched: missing locking in sched_domains code
Subject: [PATCH] sched: fix locking in arch_reinit_sched_domains

From: Heiko Carstens <heiko.carstens@de.ibm.com>

Concurrent calls to detach_destroy_domains and arch_init_sched_domains
were prevented by the old scheduler subsystem cpu hotplug mutex. When
this got converted to get_online_cpus() the locking got broken.
Unlike before now several processes can concurrently enter the critical
sections that were protected by the old lock.

So use the already present doms_cur_mutex to protect these sections again.

Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
kernel/sched.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -311,6 +311,16 @@ static DEFINE_SPINLOCK(task_group_lock);
/* doms_cur_mutex serializes access to doms_cur[] array */
static DEFINE_MUTEX(doms_cur_mutex);

+static inline void lock_doms_cur(void)
+{
+ mutex_lock(&doms_cur_mutex);
+}
+
+static inline void unlock_doms_cur(void)
+{
+ mutex_unlock(&doms_cur_mutex);
+}
+
#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_USER_SCHED
# define INIT_TASK_GROUP_LOAD (2*NICE_0_LOAD)
@@ -358,21 +368,9 @@ static inline void set_task_rq(struct ta
#endif
}

-static inline void lock_doms_cur(void)
-{
- mutex_lock(&doms_cur_mutex);
-}
-
-static inline void unlock_doms_cur(void)
-{
- mutex_unlock(&doms_cur_mutex);
-}
-
#else

static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
-static inline void lock_doms_cur(void) { }
-static inline void unlock_doms_cur(void) { }

#endif /* CONFIG_GROUP_SCHED */

@@ -7813,8 +7811,10 @@ int arch_reinit_sched_domains(void)
int err;

get_online_cpus();
+ lock_doms_cur();
detach_destroy_domains(&cpu_online_map);
err = arch_init_sched_domains(&cpu_online_map);
+ unlock_doms_cur();
put_online_cpus();

return err;

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