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

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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>
This commit is contained in:
David Rientjes 2015-09-08 15:00:42 -07:00 • committed by Linus Torvalds
parent 54e9e29132
commit 071a4befeb
2 changed files with 7 additions and 3 deletions
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3
Documentation/sysrq.txt
View file

@ -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. '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) 'g' - Used by kgdb (kernel debugger)

7
mm/oom_kill.c
View file

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