mm, oom: do not panic for oom kills triggered from sysrq

Sysrq+f is used to kill a process either for debug or when the VM is otherwise unresponsive. It is not intended to trigger a panic when no process may be killed. Avoid panicking the system for sysrq+f when no processes are killed. Signed-off-by: David Rientjes <[email protected]> Suggested-by: Michal Hocko <[email protected]> Cc: Sergey Senozhatsky <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
CamonZ · Sep 8, 2015 · 071a4be · 071a4be
1 parent 54e9e29
commit 071a4be
Show file tree

Hide file tree

Showing 2 changed files with 7 additions and 3 deletions.
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
@@ -75,7 +75,8 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 
 'e'     - Send a SIGTERM to all processes, except for init.
 
-'f'	- Will call oom_kill to kill a memory hog process.
+'f'	- Will call the oom killer to kill a memory hog process, but do not
+	  panic if nothing can be killed.
 
 'g'	- Used by kgdb (kernel debugger)
 

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
@@ -607,6 +607,9 @@ void check_panic_on_oom(struct oom_control *oc, enum oom_constraint constraint,
 		if (constraint != CONSTRAINT_NONE)
 			return;
 	}
+	/* Do not panic for oom kills triggered by sysrq */
+	if (oc->order == -1)
+		return;
 	dump_header(oc, NULL, memcg);
 	panic("Out of memory: %s panic_on_oom is enabled\n",
 		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
@@ -686,11 +689,11 @@ bool out_of_memory(struct oom_control *oc)
 
 	p = select_bad_process(oc, &points, totalpages);
 	/* Found nothing?!?! Either we hang forever, or we panic. */
-	if (!p) {
+	if (!p && oc->order != -1) {
 		dump_header(oc, NULL, NULL);
 		panic("Out of memory and no killable processes...\n");
 	}
-	if (p != (void *)-1UL) {
+	if (p && p != (void *)-1UL) {
 		oom_kill_process(oc, p, points, totalpages, NULL,
 				 "Out of memory");
 		killed = 1;