// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/oom_kill.c
 *
 *  Copyright (C)  1998,2000  Rik van Riel
 *	Thanks go out to Claus Fischer for some serious inspiration and
 *	for goading me into coding this file...
 *  Copyright (C)  2010  Google, Inc.
 *	Rewritten by David Rientjes
 *
 *  The routines in this file are used to kill a process when
 *  we're seriously out of memory. This gets called from __alloc_pages()
 *  in mm/page_alloc.c when we really run out of memory.
 *
 *  Since we won't call these routines often (on a well-configured
 *  machine) this file will double as a 'coding guide' and a signpost
 *  for newbie kernel hackers. It features several pointers to major
 *  kernel subsystems and hints as to where to find out what things do.
 */

/*
 * Official Linux v6.18: mm/oom_kill.c
 * https://github.com/torvalds/linux/blob/v6.18/mm/oom_kill.c#L1023
 * Complete upstream scope, not an elided book-code reconstruction.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

static void oom_kill_process(struct oom_control *oc, const char *message)
{
	struct task_struct *victim = oc->chosen;
	struct mem_cgroup *oom_group;
	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
					      DEFAULT_RATELIMIT_BURST);

	/*
	 * If the task is already exiting, don't alarm the sysadmin or kill
	 * its children or threads, just give it access to memory reserves
	 * so it can die quickly
	 */
	task_lock(victim);
	if (task_will_free_mem(victim)) {
		mark_oom_victim(victim);
		queue_oom_reaper(victim);
		task_unlock(victim);
		put_task_struct(victim);
		return;
	}
	task_unlock(victim);

	if (__ratelimit(&oom_rs)) {
		dump_header(oc);
		dump_oom_victim(oc, victim);
	}

	/*
	 * Do we need to kill the entire memory cgroup?
	 * Or even one of the ancestor memory cgroups?
	 * Check this out before killing the victim task.
	 */
	oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);

	__oom_kill_process(victim, message);

	/*
	 * If necessary, kill all tasks in the selected memory cgroup.
	 */
	if (oom_group) {
		memcg_memory_event(oom_group, MEMCG_OOM_GROUP_KILL);
		mem_cgroup_print_oom_group(oom_group);
		mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
				      (void *)message);
		mem_cgroup_put(oom_group);
	}
}