From 2935062be77113c1c4565ca9d0c72180449aafee Mon Sep 17 00:00:00 2001 From: Kuba Piecuch Date: Mon, 12 Oct 2026 21:07:46 +0000 Subject: [PATCH] sched_ext: Wait for SCX_OPSS_DISPATCHING before moving tasks off DSQs A task can be found on a non-local DSQ while the CPU which dispatched it is still running ops.dequeue() and hasn't cleared SCX_OPSS_DISPATCHING. The DSQ consume and move paths don't wait for the dispatch to finish and can operate on the task concurrently with the dispatcher. Call scx_wait_dispatching() in scx_move_local_task_to_local_dsq(), unlink_dsq_and_switch_rq_lock() and move_task_between_dsqs() before they operate on the task. In scx_move_local_task_to_local_dsq(), wait before scx_resolve_local_dsq() as it may update p->scx.flags. Fixes: ebf1ccff79c4 ("sched_ext: Fix ops.dequeue() semantics") Fixes: cb86607ada73 ("sched_ext: Don't run ops.dequeue() with a DSQ lock held") Cc: stable@vger.kernel.org # v7.1+ Reviewed-by: Andrea Righi Assisted-by: Claude:claude-opus-5.5 Signed-off-by: Kuba Piecuch Signed-off-by: Tejun Heo --- kernel/sched/ext/ext.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index cf6c9fead433..91120fc17d30 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -2407,11 +2407,14 @@ static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p, int wake_fl void scx_move_local_task_to_local_dsq(struct scx_sched *sch, struct task_struct *p, u64 enq_flags, struct rq *dst_rq) { - struct scx_dispatch_q *dst_dsq = scx_resolve_local_dsq(sch, dst_rq, p, &enq_flags); + struct scx_dispatch_q *dst_dsq; lockdep_assert_rq_held(dst_rq); WARN_ON_ONCE(p->scx.holding_cpu >= 0); + scx_wait_dispatching(p); + + dst_dsq = scx_resolve_local_dsq(sch, dst_rq, p, &enq_flags); if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) dsq_insert_head(dst_dsq, p); @@ -2591,8 +2594,12 @@ static bool unlink_dsq_and_switch_rq_lock(struct task_struct *p, switch_rq_lock(locked_rq, src_rq); /* task_rq couldn't have changed if we're still the holding cpu */ - return likely(p->scx.holding_cpu == cpu) && - !WARN_ON_ONCE(src_rq != task_rq(p)); + if (likely(p->scx.holding_cpu == cpu) && !WARN_ON_ONCE(src_rq != task_rq(p))) { + scx_wait_dispatching(p); + return true; + } + + return false; } static bool consume_remote_task(struct scx_sched *sch, struct rq *this_rq, @@ -2635,6 +2642,8 @@ static struct rq *move_task_between_dsqs(struct scx_sched *sch, lockdep_assert_held(&src_dsq->lock); lockdep_assert_rq_held(src_rq); + scx_wait_dispatching(p); + if (dst_dsq->id == SCX_DSQ_LOCAL) { dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); if (src_rq != dst_rq &&