Commit d73d0035 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Andrew Morton
Browse files

memcg: mm_update_next_owner: move for_each_thread() into try_to_set_owner() 

mm_update_next_owner() checks the children / real_parent->children to
avoid the "everything else" loop in the likely case, but this won't work
if a child/sibling has a zombie leader with ->mm == NULL.

Move the for_each_thread() logic into try_to_set_owner(), if nothing else
this makes the children/siblings/everything searches more consistent.

Link: https://lkml.kernel.org/r/20240626152930.GA17936@redhat.com


Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jinliang Zheng <alexjlzheng@tencent.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Tycho Andersen <tandersen@netflix.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 2a22b773

kernel/exit.c

+24 −16
Original line number Diff line number Diff line
@@ -440,7 +440,7 @@ static void coredump_task_exit(struct task_struct *tsk) 


#ifdef CONFIG_MEMCG

/* drops tasklist_lock if succeeds */

static bool try_to_set_owner(struct task_struct *tsk, struct mm_struct *mm)

static bool __try_to_set_owner(struct task_struct *tsk, struct mm_struct *mm)

{

	bool ret = false;
@@ -456,12 +456,28 @@ static bool try_to_set_owner(struct task_struct *tsk, struct mm_struct *mm) 
	return ret;

}



static bool try_to_set_owner(struct task_struct *g, struct mm_struct *mm)

{

	struct task_struct *t;



	for_each_thread(g, t) {

		struct mm_struct *t_mm = READ_ONCE(t->mm);

		if (t_mm == mm) {

			if (__try_to_set_owner(t, mm))

				return true;

		} else if (t_mm)

			break;

	}



	return false;

}



/*

 * A task is exiting.   If it owned this mm, find a new owner for the mm.

 */

void mm_update_next_owner(struct mm_struct *mm)

{

	struct task_struct *c, *g, *p = current;

	struct task_struct *g, *p = current;



	/*

	 * If the exiting or execing task is not the owner, it's
@@ -483,19 +499,17 @@ void mm_update_next_owner(struct mm_struct *mm) 
	/*

	 * Search in the children

	 */

	list_for_each_entry(c, &p->children, sibling) {

		if (c->mm == mm && try_to_set_owner(c, mm))

	list_for_each_entry(g, &p->children, sibling) {

		if (try_to_set_owner(g, mm))

			goto ret;

	}



	/*

	 * Search in the siblings

	 */

	list_for_each_entry(c, &p->real_parent->children, sibling) {

		if (c->mm == mm && try_to_set_owner(c, mm))

	list_for_each_entry(g, &p->real_parent->children, sibling) {

		if (try_to_set_owner(g, mm))

			goto ret;

	}



	/*

	 * Search through everything else, we should not get here often.

	 */
@@ -504,14 +518,8 @@ void mm_update_next_owner(struct mm_struct *mm) 
			break;

		if (g->flags & PF_KTHREAD)

			continue;

		for_each_thread(g, c) {

			struct mm_struct *c_mm = READ_ONCE(c->mm);

			if (c_mm == mm) {

				if (try_to_set_owner(c, mm))

		if (try_to_set_owner(g, mm))

			goto ret;

			} else if (c_mm)

				break;

		}

	}

	read_unlock(&tasklist_lock);

	/*