oom: dump stack and VM state when oom killer panics

The oom killer header, including information such as the allocation order
and gfp mask, current's cpuset and memory controller, call trace, and VM
state information is currently only shown when the oom killer has selected
a task to kill.

This information is omitted, however, when the oom killer panics either
because of panic_on_oom sysctl settings or when no killable task was
found.  It is still relevant to know crucial pieces of information such as
the allocation order and VM state when diagnosing such issues, especially
at boot.

This patch displays the oom killer header whenever it panics so that bug
reports can include pertinent information to debug the issue, if possible.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -337,6 +337,21 @@ static void dump_tasks(const struct mem_cgroup *mem)
 	} while_each_thread(g, p);
 }
 
+static void dump_header(gfp_t gfp_mask, int order, struct mem_cgroup *mem)
+{
+	pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
+		"oom_adj=%d\n",
+		current->comm, gfp_mask, order, current->signal->oom_adj);
+	task_lock(current);
+	cpuset_print_task_mems_allowed(current);
+	task_unlock(current);
+	dump_stack();
+	mem_cgroup_print_oom_info(mem, current);
+	show_mem();
+	if (sysctl_oom_dump_tasks)
+		dump_tasks(mem);
+}
+
 /*
  * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
@@ -395,20 +410,8 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 {
 	struct task_struct *c;
 
-	if (printk_ratelimit()) {
-		printk(KERN_WARNING "%s invoked oom-killer: "
-			"gfp_mask=0x%x, order=%d, oom_adj=%d\n",
-			current->comm, gfp_mask, order,
-			current->signal->oom_adj);
-		task_lock(current);
-		cpuset_print_task_mems_allowed(current);
-		task_unlock(current);
-		dump_stack();
-		mem_cgroup_print_oom_info(mem, current);
-		show_mem();
-		if (sysctl_oom_dump_tasks)
-			dump_tasks(mem);
-	}
+	if (printk_ratelimit())
+		dump_header(gfp_mask, order, mem);
 
 	/*
 	 * If the task is already exiting, don't alarm the sysadmin or kill
@@ -544,6 +547,7 @@ retry:
 	/* Found nothing?!?! Either we hang forever, or we panic. */
 	if (!p) {
 		read_unlock(&tasklist_lock);
+		dump_header(gfp_mask, order, NULL);
 		panic("Out of memory and no killable processes...\n");
 	}
 
@@ -609,8 +613,10 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
 		/* Got some memory back in the last second. */
 		return;
 
-	if (sysctl_panic_on_oom == 2)
+	if (sysctl_panic_on_oom == 2) {
+		dump_header(gfp_mask, order, NULL);
 		panic("out of memory. Compulsory panic_on_oom is selected.\n");
+	}
 
 	/*
 	 * Check if there were limitations on the allocation (only relevant for
@@ -626,8 +632,10 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
 		break;
 
 	case CONSTRAINT_NONE:
-		if (sysctl_panic_on_oom)
+		if (sysctl_panic_on_oom) {
+			dump_header(gfp_mask, order, NULL);
 			panic("out of memory. panic_on_oom is selected\n");
+		}
 		/* Fall-through */
 	case CONSTRAINT_CPUSET:
 		__out_of_memory(gfp_mask, order);