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 <rientjes@google.com>
Suggested-by: Michal Hocko <mhocko@suse.cz>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 7 insertions, 3 deletions

diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 267f39386f99..13f5619b2203 100644
--- 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
index 77adc8e876aa..91dd59f63910 100644
--- 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;