> 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@xxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> 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");
> }
Given sysctl_panic_on_oom checked, AFAICU there seems
no chance for panic, no matter -1 or not.
> - 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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