Commit 60f21a26 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup, sched_ext: Include exiting tasks in cgroup iter 



a72f73c4 ("cgroup: Don't expose dead tasks in cgroup") made
css_task_iter_advance() skip exiting tasks so cgroup.procs stays consistent
with waitpid() visibility. Unfortunately, this broke scx_task_iter.

scx_task_iter walks either scx_tasks (global) or a cgroup subtree via
css_task_iter() and the two modes are expected to cover the same set of
tasks. After the above change the cgroup-scoped mode silently skips tasks
past exit_signals() that are still on scx_tasks.

scx_sub_enable_workfn()'s abort path is one of the symptoms: an exiting
SCX_TASK_SUB_INIT task can race past the cgroup iter leaking
__scx_init_task() state. Other iterations share the same gap.

Add CSS_TASK_ITER_WITH_DEAD to opt out of the skip and use it from
scx_task_iter().

Fixes: b0e4c2f8 ("sched_ext: Implement cgroup subtree iteration for scx_task_iter")
Reported-by: default avatarCheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent d99f7a32

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ struct kernel_clone_args; 
enum css_task_iter_flags {

	CSS_TASK_ITER_PROCS    = (1U << 0),  /* walk only threadgroup leaders */

	CSS_TASK_ITER_THREADED = (1U << 1),  /* walk all threaded css_sets in the domain */

	CSS_TASK_ITER_WITH_DEAD = (1U << 2),  /* include exiting tasks */

	CSS_TASK_ITER_SKIPPED  = (1U << 16), /* internal flags */

};

kernel/cgroup/cgroup.c

+5 −3
Original line number Diff line number Diff line
@@ -5059,10 +5059,12 @@ static void css_task_iter_advance(struct css_task_iter *it) 


	task = list_entry(it->task_pos, struct task_struct, cg_list);

	/*

	 * Hide tasks that are exiting but not yet removed. Keep zombie

	 * leaders with live threads visible.

	 * Hide tasks that are exiting but not yet removed by default. Keep

	 * zombie leaders with live threads visible. Usages that need to walk

	 * every existing task can opt out via CSS_TASK_ITER_WITH_DEAD.

	 */

	if ((task->flags & PF_EXITING) && !atomic_read(&task->signal->live))

	if (!(it->flags & CSS_TASK_ITER_WITH_DEAD) &&

	    (task->flags & PF_EXITING) && !atomic_read(&task->signal->live))

		goto repeat;



	if (it->flags & CSS_TASK_ITER_PROCS) {

kernel/sched/ext.c

+4 −2
Original line number Diff line number Diff line
@@ -766,7 +766,8 @@ static void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp) 
		lockdep_assert_held(&cgroup_mutex);

		iter->cgrp = cgrp;

		iter->css_pos = css_next_descendant_pre(NULL, &iter->cgrp->self);

		css_task_iter_start(iter->css_pos, 0, &iter->css_iter);

		css_task_iter_start(iter->css_pos, CSS_TASK_ITER_WITH_DEAD,

				    &iter->css_iter);

		return;

	}

#endif
@@ -866,7 +867,8 @@ static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter) 
			iter->css_pos = css_next_descendant_pre(iter->css_pos,

								&iter->cgrp->self);

			if (iter->css_pos)

				css_task_iter_start(iter->css_pos, 0, &iter->css_iter);

				css_task_iter_start(iter->css_pos, CSS_TASK_ITER_WITH_DEAD,

						    &iter->css_iter);

		}

		return NULL;

	}