Merge branch 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu

Pull percpu fixes from Tejun Heo:
 "While adding GFP_ATOMIC support to the percpu allocator, the
  synchronization for the fast-path which doesn't require external
  allocations was separated into pcpu_lock.

  Unfortunately, it incorrectly decoupled async paths and percpu
  chunks could get destroyed while still being operated on.  This
  contains two patches to fix the bug"

* 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
  percpu: fix synchronization between synchronous map extension and chunk destruction
  percpu: fix synchronization between chunk->map_extend_work and chunk destruction

1 files changed, 44 insertions, 29 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 0c59684f1ff2..9903830aaebb 100644
--- a/mm/percpu.c
+++ b/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_chunk;
 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 pcpu_chunk *chunk, bool is_atomic)
 {
         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 pcpu_chunk *chunk, int new_alloc)
         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_chunk(void)
         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 size, size_t align, bool reserved,
                 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 work_struct *work)
                 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 +1142,25 @@ static void pcpu_balance_workfn(struct work_struct *work)
                 pcpu_destroy_chunk(chunk);
         }
 
+        /* service chunks which requested async area map extension */
+        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 +1659,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
          */
         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 +1688,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
         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);