Commit bd2d7645 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Defer scx_hardlockup() out of NMI 



scx_hardlockup() runs from NMI and eventually calls scx_claim_exit(),
which takes scx_sched_lock. scx_sched_lock isn't NMI-safe and grabbing
it from NMI context can lead to deadlocks.

The hardlockup handler is best-effort recovery and the disable path it
triggers runs off of irq_work anyway. Move the handle_lockup() call into
an irq_work so it runs in IRQ context.

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 510a2705

kernel/sched/ext.c

+27 −6
Original line number Diff line number Diff line
@@ -4940,6 +4940,25 @@ void scx_softlockup(u32 dur_s) 
			smp_processor_id(), dur_s);

}



/*

 * scx_hardlockup() runs from NMI and eventually calls scx_claim_exit(),

 * which takes scx_sched_lock. scx_sched_lock isn't NMI-safe and grabbing

 * it from NMI context can lead to deadlocks. Defer via irq_work; the

 * disable path runs off irq_work anyway.

 */

static atomic_t scx_hardlockup_cpu = ATOMIC_INIT(-1);



static void scx_hardlockup_irq_workfn(struct irq_work *work)

{

	int cpu = atomic_xchg(&scx_hardlockup_cpu, -1);



	if (cpu >= 0 && handle_lockup("hard lockup - CPU %d", cpu))

		printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n",

				cpu);

}



static DEFINE_IRQ_WORK(scx_hardlockup_irq_work, scx_hardlockup_irq_workfn);



/**

 * scx_hardlockup - sched_ext hardlockup handler

 *
@@ -4948,17 +4967,19 @@ void scx_softlockup(u32 dur_s) 
 * Try kicking out the current scheduler in an attempt to recover the system to

 * a good state before taking more drastic actions.

 *

 * Returns %true if sched_ext is enabled and abort was initiated, which may

 * resolve the reported hardlockup. %false if sched_ext is not enabled or

 * someone else already initiated abort.

 * Queues an irq_work; the handle_lockup() call happens in IRQ context (see

 * scx_hardlockup_irq_workfn).

 *

 * Returns %true if sched_ext is enabled and the work was queued, %false

 * otherwise.

 */

bool scx_hardlockup(int cpu)

{

	if (!handle_lockup("hard lockup - CPU %d", cpu))

	if (!rcu_access_pointer(scx_root))

		return false;



	printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n",

			cpu);

	atomic_cmpxchg(&scx_hardlockup_cpu, -1, cpu);

	irq_work_queue(&scx_hardlockup_irq_work);

	return true;

}