Commit 6b4576b0 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Reject sub-sched attachment to a disabled parent 



scx_claim_exit() propagates exits to descendants under scx_sched_lock.
A sub-sched being attached concurrently could be missed if it links
after the propagation. Check the parent's exit_kind in scx_link_sched()
under scx_sched_lock to interlock against scx_claim_exit() - either the
parent sees the child in its iteration or the child sees the parent's
non-NONE exit_kind and fails attachment.

Fixes: ebeca1f9 ("sched_ext: Introduce cgroup sub-sched support")
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
parent 6b36c4c2

kernel/sched/ext.c

+16 −0
Original line number Diff line number Diff line
@@ -5247,6 +5247,17 @@ static s32 scx_link_sched(struct scx_sched *sch) 
		s32 ret;



		if (parent) {

			/*

			 * scx_claim_exit() propagates exit_kind transition to

			 * its sub-scheds while holding scx_sched_lock - either

			 * we can see the parent's non-NONE exit_kind or the

			 * parent can shoot us down.

			 */

			if (atomic_read(&parent->exit_kind) != SCX_EXIT_NONE) {

				scx_error(sch, "parent disabled");

				return -ENOENT;

			}



			ret = rhashtable_lookup_insert_fast(&scx_sched_hash,

					&sch->hash_node, scx_sched_hash_params);

			if (ret) {
@@ -5638,6 +5649,11 @@ static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind) 
	 * serialized, running them in separate threads allows parallelizing

	 * ops.exit(), which can take arbitrarily long prolonging bypass mode.

	 *

	 * To guarantee forward progress, this propagation must be in-line so

	 * that ->aborting is synchronously asserted for all sub-scheds. The

	 * propagation is also the interlocking point against sub-sched

	 * attachment. See scx_link_sched().

	 *

	 * This doesn't cause recursions as propagation only takes place for

	 * non-propagation exits.

	 */