oom: print triggering task's cpuset and mems allowed

When cpusets are enabled, it's necessary to print the triggering task's
set of allowable nodes so the subsequently printed meminfo can be
interpreted correctly.

We also print the task's cpuset name for informational purposes.

[rientjes@google.com: task lock current before dereferencing cpuset]
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cpuset.h

@@ -78,6 +78,8 @@ extern int current_cpuset_is_being_rebound(void);
 
 extern void rebuild_sched_domains(void);
 
+extern void cpuset_print_task_mems_allowed(struct task_struct *p);
+
 #else /* !CONFIG_CPUSETS */
 
 static inline int cpuset_init_early(void) { return 0; }
@@ -159,6 +161,10 @@ static inline void rebuild_sched_domains(void)
 	partition_sched_domains(1, NULL, NULL);
 }
 
+static inline void cpuset_print_task_mems_allowed(struct task_struct *p)
+{
+}
+
 #endif /* !CONFIG_CPUSETS */
 
 #endif /* _LINUX_CPUSET_H */

kernel/cpuset.c

@@ -239,6 +239,17 @@ static struct cpuset top_cpuset = {
 
 static DEFINE_MUTEX(callback_mutex);
 
+/*
+ * cpuset_buffer_lock protects both the cpuset_name and cpuset_nodelist
+ * buffers.  They are statically allocated to prevent using excess stack
+ * when calling cpuset_print_task_mems_allowed().
+ */
+#define CPUSET_NAME_LEN		(128)
+#define	CPUSET_NODELIST_LEN	(256)
+static char cpuset_name[CPUSET_NAME_LEN];
+static char cpuset_nodelist[CPUSET_NODELIST_LEN];
+static DEFINE_SPINLOCK(cpuset_buffer_lock);
+
 /*
  * This is ugly, but preserves the userspace API for existing cpuset
  * users. If someone tries to mount the "cpuset" filesystem, we
@@ -2356,6 +2367,29 @@ int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
 	return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
 }
 
+/**
+ * cpuset_print_task_mems_allowed - prints task's cpuset and mems_allowed
+ * @task: pointer to task_struct of some task.
+ *
+ * Description: Prints @task's name, cpuset name, and cached copy of its
+ * mems_allowed to the kernel log.  Must hold task_lock(task) to allow
+ * dereferencing task_cs(task).
+ */
+void cpuset_print_task_mems_allowed(struct task_struct *tsk)
+{
+	struct dentry *dentry;
+
+	dentry = task_cs(tsk)->css.cgroup->dentry;
+	spin_lock(&cpuset_buffer_lock);
+	snprintf(cpuset_name, CPUSET_NAME_LEN,
+		 dentry ? (const char *)dentry->d_name.name : "/");
+	nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
+			   tsk->mems_allowed);
+	printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
+	       tsk->comm, cpuset_name, cpuset_nodelist);
+	spin_unlock(&cpuset_buffer_lock);
+}
+
 /*
  * Collection of memory_pressure is suppressed unless
  * this flag is enabled by writing "1" to the special

mm/oom_kill.c

@@ -392,6 +392,9 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		printk(KERN_WARNING "%s invoked oom-killer: "
 			"gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
 			current->comm, gfp_mask, order, current->oomkilladj);
+		task_lock(current);
+		cpuset_print_task_mems_allowed(current);
+		task_unlock(current);
 		dump_stack();
 		show_mem();
 		if (sysctl_oom_dump_tasks)