Thanks.

Index: work/mm/percpu.c
===================================================================

--- work.orig/mm/percpu.c
+++ work/mm/percpu.c

@@ -112,7 +112,7 @@ struct pcpu_chunk {
        int                     map_used;       /* # of map entries used before the sentry */
        int                     map_alloc;      /* # of map entries allocated */
        int                     *map;           /* allocation map */
-       struct work_struct      map_extend_work;/* async ->map[] extension */
+       struct list_head        map_extend_list;/* on pcpu_map_extend_chunks */

        void                    *data;          /* chunk data */
        int                     first_free;     /* no free below this */

@@ -162,10 +162,13 @@ static struct pcpu_chunk *pcpu_reserved_
 static int pcpu_reserved_chunk_limit;

 static DEFINE_SPINLOCK(pcpu_lock);     /* all internal data structures */
-static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop */
+static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop, map ext */

 static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */

+/* chunks which need their map areas extended, protected by pcpu_lock */
+static LIST_HEAD(pcpu_map_extend_chunks);
+
 /*
  * The number of empty populated pages, protected by pcpu_lock.  The
  * reserved chunk doesn't contribute to the count.

@@ -395,13 +398,19 @@ static int pcpu_need_to_extend(struct pc
 {
        int margin, new_alloc;

+       lockdep_assert_held(&pcpu_lock);
+
        if (is_atomic) {
                margin = 3;

                if (chunk->map_alloc <
-                   chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW &&
-                   pcpu_async_enabled)
-                       schedule_work(&chunk->map_extend_work);
+                   chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) {
+                       if (list_empty(&chunk->map_extend_list)) {
+                               list_add_tail(&chunk->map_extend_list,
+                                             &pcpu_map_extend_chunks);
+                               pcpu_schedule_balance_work();
+                       }
+               }
        } else {
                margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;
        }

@@ -435,6 +444,8 @@ static int pcpu_extend_area_map(struct p
        size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
        unsigned long flags;

+       lockdep_assert_held(&pcpu_alloc_mutex);
+
        new = pcpu_mem_zalloc(new_size);
        if (!new)
                return -ENOMEM;

@@ -467,20 +478,6 @@ out_unlock:
        return 0;
 }

-static void pcpu_map_extend_workfn(struct work_struct *work)
-{
-       struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk,
-                                               map_extend_work);
-       int new_alloc;
-
-       spin_lock_irq(&pcpu_lock);
-       new_alloc = pcpu_need_to_extend(chunk, false);
-       spin_unlock_irq(&pcpu_lock);
-
-       if (new_alloc)
-               pcpu_extend_area_map(chunk, new_alloc);
-}
-
 /**
  * pcpu_fit_in_area - try to fit the requested allocation in a candidate area
  * @chunk: chunk the candidate area belongs to

@@ -740,7 +737,7 @@ static struct pcpu_chunk *pcpu_alloc_chu
        chunk->map_used = 1;

        INIT_LIST_HEAD(&chunk->list);
-       INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn);
+       INIT_LIST_HEAD(&chunk->map_extend_list);
        chunk->free_size = pcpu_unit_size;
        chunk->contig_hint = pcpu_unit_size;

@@ -895,6 +892,9 @@ static void __percpu *pcpu_alloc(size_t
                return NULL;
        }

+       if (!is_atomic)
+               mutex_lock(&pcpu_alloc_mutex);
+
        spin_lock_irqsave(&pcpu_lock, flags);

        /* serve reserved allocations from the reserved chunk if available */

@@ -967,12 +967,9 @@ restart:
        if (is_atomic)
                goto fail;

-       mutex_lock(&pcpu_alloc_mutex);
-
        if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
                chunk = pcpu_create_chunk();
                if (!chunk) {
-                       mutex_unlock(&pcpu_alloc_mutex);
                        err = "failed to allocate new chunk";
                        goto fail;
                }

@@ -983,7 +980,6 @@ restart:
                spin_lock_irqsave(&pcpu_lock, flags);
        }

-       mutex_unlock(&pcpu_alloc_mutex);
        goto restart;

 area_found:

@@ -993,8 +989,6 @@ area_found:
        if (!is_atomic) {
                int page_start, page_end, rs, re;

-               mutex_lock(&pcpu_alloc_mutex);
-
                page_start = PFN_DOWN(off);
                page_end = PFN_UP(off + size);

@@ -1005,7 +999,6 @@ area_found:

                        spin_lock_irqsave(&pcpu_lock, flags);
                        if (ret) {
-                               mutex_unlock(&pcpu_alloc_mutex);
                                pcpu_free_area(chunk, off, &occ_pages);
                                err = "failed to populate";
                                goto fail_unlock;

@@ -1045,6 +1038,8 @@ fail:
                /* see the flag handling in pcpu_blance_workfn() */
                pcpu_atomic_alloc_failed = true;
                pcpu_schedule_balance_work();
+       } else {
+               mutex_unlock(&pcpu_alloc_mutex);
        }
        return NULL;
 }

@@ -1129,6 +1124,7 @@ static void pcpu_balance_workfn(struct w
                if (chunk == list_first_entry(free_head, struct pcpu_chunk, list))
                        continue;

+               list_del_init(&chunk->map_extend_list);
                list_move(&chunk->list, &to_free);
        }

@@ -1146,6 +1142,24 @@ static void pcpu_balance_workfn(struct w
                pcpu_destroy_chunk(chunk);
        }

+       do {
+               int new_alloc = 0;
+
+               spin_lock_irq(&pcpu_lock);
+
+               chunk = list_first_entry_or_null(&pcpu_map_extend_chunks,
+                                       struct pcpu_chunk, map_extend_list);
+               if (chunk) {
+                       list_del_init(&chunk->map_extend_list);
+                       new_alloc = pcpu_need_to_extend(chunk, false);
+               }
+
+               spin_unlock_irq(&pcpu_lock);
+
+               if (new_alloc)
+                       pcpu_extend_area_map(chunk, new_alloc);
+       } while (chunk);
+
        /*
         * Ensure there are certain number of free populated pages for
         * atomic allocs.  Fill up from the most packed so that atomic

@@ -1644,7 +1658,7 @@ int __init pcpu_setup_first_chunk(const
         */
        schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
        INIT_LIST_HEAD(&schunk->list);
-       INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn);
+       INIT_LIST_HEAD(&schunk->map_extend_list);
        schunk->base_addr = base_addr;
        schunk->map = smap;
        schunk->map_alloc = ARRAY_SIZE(smap);

@@ -1673,7 +1687,7 @@ int __init pcpu_setup_first_chunk(const
        if (dyn_size) {
                dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
                INIT_LIST_HEAD(&dchunk->list);
-               INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn);
+               INIT_LIST_HEAD(&dchunk->map_extend_list);
                dchunk->base_addr = base_addr;
                dchunk->map = dmap;
                dchunk->map_alloc = ARRAY_SIZE(dmap);