Commit 4a6c5607 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: Make sure that wq_unbound_cpumask is never empty 



During boot, depending on how the housekeeping and workqueue.unbound_cpus
masks are set, wq_unbound_cpumask can end up empty. Since 8639eceb
("workqueue: Implement non-strict affinity scope for unbound workqueues"),
this may end up feeding -1 as a CPU number into scheduler leading to oopses.

  BUG: unable to handle page fault for address: ffffffff8305e9c0
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  ...
  Call Trace:
   <TASK>
   select_idle_sibling+0x79/0xaf0
   select_task_rq_fair+0x1cb/0x7b0
   try_to_wake_up+0x29c/0x5c0
   wake_up_process+0x19/0x20
   kick_pool+0x5e/0xb0
   __queue_work+0x119/0x430
   queue_work_on+0x29/0x30
  ...

An empty wq_unbound_cpumask is a clear misconfiguration and already
disallowed once system is booted up. Let's warn on and ignore
unbound_cpumask restrictions which lead to no unbound cpus. While at it,
also remove now unncessary empty check on wq_unbound_cpumask in
wq_select_unbound_cpu().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-and-Tested-by: default avatarYong He <alexyonghe@tencent.com>
Link: http://lkml.kernel.org/r/20231120121623.119780-1-alexyonghe@tencent.com


Fixes: 8639eceb ("workqueue: Implement non-strict affinity scope for unbound workqueues")
Cc: stable@vger.kernel.org # v6.6+
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
parent a12deb44

kernel/workqueue.c

+15 −7
Original line number Diff line number Diff line
@@ -1684,9 +1684,6 @@ static int wq_select_unbound_cpu(int cpu) 
		pr_warn_once("workqueue: round-robin CPU selection forced, expect performance impact\n");

	}



	if (cpumask_empty(wq_unbound_cpumask))

		return cpu;



	new_cpu = __this_cpu_read(wq_rr_cpu_last);

	new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);

	if (unlikely(new_cpu >= nr_cpu_ids)) {
@@ -6515,6 +6512,17 @@ static inline void wq_watchdog_init(void) { } 


#endif	/* CONFIG_WQ_WATCHDOG */



static void __init restrict_unbound_cpumask(const char *name, const struct cpumask *mask)

{

	if (!cpumask_intersects(wq_unbound_cpumask, mask)) {

		pr_warn("workqueue: Restricting unbound_cpumask (%*pb) with %s (%*pb) leaves no CPU, ignoring\n",

			cpumask_pr_args(wq_unbound_cpumask), name, cpumask_pr_args(mask));

		return;

	}



	cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, mask);

}



/**

 * workqueue_init_early - early init for workqueue subsystem

 *
@@ -6534,11 +6542,11 @@ void __init workqueue_init_early(void) 
	BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));



	BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));

	cpumask_copy(wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_WQ));

	cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_DOMAIN));



	cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);

	restrict_unbound_cpumask("HK_TYPE_WQ", housekeeping_cpumask(HK_TYPE_WQ));

	restrict_unbound_cpumask("HK_TYPE_DOMAIN", housekeeping_cpumask(HK_TYPE_DOMAIN));

	if (!cpumask_empty(&wq_cmdline_cpumask))

		cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, &wq_cmdline_cpumask);

		restrict_unbound_cpumask("workqueue.unbound_cpus", &wq_cmdline_cpumask);



	pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);