Commit 57ccf5cc authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Fix enqueue_task_scx() truncation of upper enqueue flags 



enqueue_task_scx() takes int enq_flags from the sched_class interface.
SCX enqueue flags starting at bit 32 (SCX_ENQ_PREEMPT and above) are
silently truncated when passed through activate_task(). extra_enq_flags
was added as a workaround - storing high bits in rq->scx.extra_enq_flags
and OR-ing them back in enqueue_task_scx(). However, the OR target is
still the int parameter, so the high bits are lost anyway.

The current impact is limited as the only affected flag is SCX_ENQ_PREEMPT
which is informational to the BPF scheduler - its loss means the scheduler
doesn't know about preemption but doesn't cause incorrect behavior.

Fix by renaming the int parameter to core_enq_flags and introducing a
u64 enq_flags local that merges both sources. All downstream functions
already take u64 enq_flags.

Fixes: f0e1a064 ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Acked-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 2a0596d5

kernel/sched/ext.c

+2 −3
Original line number Diff line number Diff line
@@ -1470,16 +1470,15 @@ static void clr_task_runnable(struct task_struct *p, bool reset_runnable_at) 
		p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT;

}



static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags)

static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_flags)

{

	struct scx_sched *sch = scx_root;

	int sticky_cpu = p->scx.sticky_cpu;

	u64 enq_flags = core_enq_flags | rq->scx.extra_enq_flags;



	if (enq_flags & ENQUEUE_WAKEUP)

		rq->scx.flags |= SCX_RQ_IN_WAKEUP;



	enq_flags |= rq->scx.extra_enq_flags;



	if (sticky_cpu >= 0)

		p->scx.sticky_cpu = -1;