linux-kernel - [patch v3 3/3] mm, oom: do not panic for oom kills triggered from sysrq

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Message-ID: <alpine.DEB.2.10.1507081642250.16585@chino.kir.corp.google.com>
Date:	Wed, 8 Jul 2015 16:42:47 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [patch v3 3/3] 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.

Suggested-by: Michal Hocko <mhocko@...e.cz>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 v2: no change
 v3: fix title per Hillf

 Documentation/sysrq.txt | 3 ++-
 mm/oom_kill.c           | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
--- 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
--- 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;
--
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