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>

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 5376623..3ae6d94 100644 (file)
--- 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 01b5e01..fca886d 100644 (file)
--- 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);