workqueue: Make sure that wq_unbound_cpumask is never empty

JIRA: https://issues.redhat.com/browse/RHEL-21798
Conflicts: A merge conflict due to missing upstream commit fef59c9
	   ("workqueue: Rename NUMA related names to use pod instead")
	   and two other subsequent workqueue commits.

commit 4a6c560
Author: Tejun Heo <[email protected]>
Date:   Tue, 21 Nov 2023 11:39:36 -1000

    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 8639ece
    ("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: Tejun Heo <[email protected]>
    Reported-and-Tested-by: Yong He <[email protected]>
    Link: http://lkml.kernel.org/r/[email protected]
    Fixes: 8639ece ("workqueue: Implement non-strict affinity scope for unbound workqueues")
    Cc: [email protected] # v6.6+
    Reviewed-by: Waiman Long <[email protected]>

Signed-off-by: Waiman Long <[email protected]>

Author: Waiman-Long

kernel/workqueue.c

@@ -1405,9 +1405,6 @@ static int wq_select_unbound_cpu(int cpu)
 		printed_dbg_warning = true;
 	}
 
-	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)) {
@@ -6048,6 +6045,17 @@ 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);
+}
+
 static void __init wq_numa_init(void)
 {
 	cpumask_var_t *tbl;
@@ -6110,11 +6118,11 @@ 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);