oom: extract panic helper function

There are various points in the oom killer where the kernel must determine
whether to panic or not.  It's better to extract this to a helper function
to remove all the confusion as to its semantics.

Also fix a call to dump_header() where tasklist_lock is not read- locked,
as required.

There's no functional change with this patch.

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

2 files changed, 30 insertions, 24 deletions

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 537662315627..3ae6d94d0540 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -22,6 +22,7 @@ enum oom_constraint {
         CONSTRAINT_NONE,
         CONSTRAINT_CPUSET,
         CONSTRAINT_MEMORY_POLICY,
+        CONSTRAINT_MEMCG,
 };
 
 extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 01b5e01e52cb..fca886d8b5fb 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -521,17 +521,40 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
         return oom_kill_task(victim);
 }
 
+/*
+ * Determines whether the kernel must panic because of the panic_on_oom sysctl.
+ */
+static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
+                                int order)
+{
+        if (likely(!sysctl_panic_on_oom))
+                return;
+        if (sysctl_panic_on_oom != 2) {
+                /*
+                 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
+                 * does not panic for cpuset, mempolicy, or memcg allocation
+                 * failures.
+                 */
+                if (constraint != CONSTRAINT_NONE)
+                        return;
+        }
+        read_lock(&tasklist_lock);
+        dump_header(NULL, gfp_mask, order, NULL);
+        read_unlock(&tasklist_lock);
+        panic("Out of memory: %s panic_on_oom is enabled\n",
+                sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
+}
+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
 {
         unsigned long points = 0;
         struct task_struct *p;
 
-        if (sysctl_panic_on_oom == 2)
-                panic("out of memory(memcg). panic_on_oom is selected.\n");
+        check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0);
         read_lock(&tasklist_lock);
 retry:
-        p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
+        p = select_bad_process(&points, mem, CONSTRAINT_MEMCG, NULL);
         if (!p || PTR_ERR(p) == -1UL)
                 goto out;
 
@@ -632,8 +655,8 @@ retry:
 
         /* Found nothing?!?! Either we hang forever, or we panic. */
         if (!p) {
-                read_unlock(&tasklist_lock);
                 dump_header(NULL, gfp_mask, order, NULL);
+                read_unlock(&tasklist_lock);
                 panic("Out of memory and no killable processes...\n");
         }
 
@@ -655,9 +678,7 @@ void pagefault_out_of_memory(void)
                 /* Got some memory back in the last second. */
                 return;
 
-        if (sysctl_panic_on_oom)
-                panic("out of memory from page fault. panic_on_oom is selected.\n");
-
+        check_panic_on_oom(CONSTRAINT_NONE, 0, 0);
         read_lock(&tasklist_lock);
         /* unknown gfp_mask and order */
         __out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
@@ -704,29 +725,13 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                 return;
         }
 
-        if (sysctl_panic_on_oom == 2) {
-                dump_header(NULL, 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
          * NUMA) that may require different handling.
          */
         constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
+        check_panic_on_oom(constraint, gfp_mask, order);
         read_lock(&tasklist_lock);
-        if (unlikely(sysctl_panic_on_oom)) {
-                /*
-                 * panic_on_oom only affects CONSTRAINT_NONE, the kernel
-                 * should not panic for cpuset or mempolicy induced memory
-                 * failures.
-                 */
-                if (constraint == CONSTRAINT_NONE) {
-                        dump_header(NULL, gfp_mask, order, NULL);
-                        read_unlock(&tasklist_lock);
-                        panic("Out of memory: panic_on_oom is enabled\n");
-                }
-        }
         __out_of_memory(gfp_mask, order, constraint, nodemask);
         read_unlock(&tasklist_lock);