[patch 9/9] oom: do not take callback_mutex

[David Rientjes <rientjes@google.com>]

Since no task descriptor's 'cpuset' field is dereferenced in the
execution of the OOM killer anymore, it is no longer necessary to take
callback_mutex.

Cc: Andrea Arcangeli <andrea@suse.de>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 include/linux/cpuset.h |    6 ------
 kernel/cpuset.c        |   27 ---------------------------
 mm/oom_kill.c          |    3 ---
 3 files changed, 0 insertions(+), 36 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -59,9 +59,6 @@ extern void __cpuset_memory_pressure_bump(void);
 extern const struct file_operations proc_cpuset_operations;
 extern char *cpuset_task_status_allowed(struct task_struct *task, char *buffer);
 
-extern void cpuset_lock(void);
-extern void cpuset_unlock(void);
-
 extern int cpuset_mem_spread_node(void);
 
 static inline int cpuset_do_page_mem_spread(void)
@@ -128,9 +125,6 @@ static inline char *cpuset_task_status_allowed(struct task_struct *task,
 	return buffer;
 }
 
-static inline void cpuset_lock(void) {}
-static inline void cpuset_unlock(void) {}
-
 static inline int cpuset_mem_spread_node(void)
 {
 	return 0;
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2501,33 +2501,6 @@ int __cpuset_zone_allowed_hardwall(struct zone *z, gfp_t gfp_mask)
 }
 
 /**
- * cpuset_lock - lock out any changes to cpuset structures
- *
- * The out of memory (oom) code needs to mutex_lock cpusets
- * from being changed while it scans the tasklist looking for a
- * task in an overlapping cpuset.  Expose callback_mutex via this
- * cpuset_lock() routine, so the oom code can lock it, before
- * locking the task list.  The tasklist_lock is a spinlock, so
- * must be taken inside callback_mutex.
- */
-
-void cpuset_lock(void)
-{
-	mutex_lock(&callback_mutex);
-}
-
-/**
- * cpuset_unlock - release lock on cpuset changes
- *
- * Undo the lock taken in a previous cpuset_lock() call.
- */
-
-void cpuset_unlock(void)
-{
-	mutex_unlock(&callback_mutex);
-}
-
-/**
  * cpuset_mem_spread_node() - On which node to begin search for a page
  *
  * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -470,7 +470,6 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
 	 * NUMA) that may require different handling.
 	 */
 	constraint = constrained_alloc(zonelist, gfp_mask);
-	cpuset_lock();
 	read_lock(&tasklist_lock);
 
 	switch (constraint) {
@@ -502,7 +501,6 @@ retry:
 		/* Found nothing?!?! Either we hang forever, or we panic. */
 		if (!p) {
 			read_unlock(&tasklist_lock);
-			cpuset_unlock();
 			panic("Out of memory and no killable processes...\n");
 		}
 
@@ -515,7 +513,6 @@ retry:
 
 out:
 	read_unlock(&tasklist_lock);
-	cpuset_unlock();
 
 	/*
 	 * Give "p" a good chance of killing itself before we

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