// 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#L618
 * Complete upstream scope, not an elided book-code reconstruction.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

static void oom_reap_task(struct task_struct *tsk)
{
	int attempts = 0;
	struct mm_struct *mm = tsk->signal->oom_mm;

	/* Retry the mmap_read_trylock(mm) a few times */
	while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
		schedule_timeout_idle(HZ/10);

	if (attempts <= MAX_OOM_REAP_RETRIES ||
	    mm_flags_test(MMF_OOM_SKIP, mm))
		goto done;

	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
		task_pid_nr(tsk), tsk->comm);
	sched_show_task(tsk);
	debug_show_all_locks();

done:
	tsk->oom_reaper_list = NULL;

	/*
	 * Hide this mm from OOM killer because it has been either reaped or
	 * somebody can't call mmap_write_unlock(mm).
	 */
	mm_flags_set(MMF_OOM_SKIP, mm);

	/* Drop a reference taken by queue_oom_reaper */
	put_task_struct(tsk);
}