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

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
  percpu: restructure pcpu_extend_area_map() to fix bugs and improve readability

1 files changed, 81 insertions, 40 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index d90797160c2a..5adfc268b408 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -355,62 +355,86 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
 }
 
 /**
- * pcpu_extend_area_map - extend area map for allocation
- * @chunk: target chunk
+ * pcpu_need_to_extend - determine whether chunk area map needs to be extended
+ * @chunk: chunk of interest
  *
- * Extend area map of @chunk so that it can accomodate an allocation.
- * A single allocation can split an area into three areas, so this
- * function makes sure that @chunk->map has at least two extra slots.
+ * Determine whether area map of @chunk needs to be extended to
+ * accomodate a new allocation.
  *
  * CONTEXT:
- * pcpu_alloc_mutex, pcpu_lock.  pcpu_lock is released and reacquired
- * if area map is extended.
+ * pcpu_lock.
  *
  * RETURNS:
- * 0 if noop, 1 if successfully extended, -errno on failure.
+ * New target map allocation length if extension is necessary, 0
+ * otherwise.
  */
-static int pcpu_extend_area_map(struct pcpu_chunk *chunk, unsigned long *flags)
+static int pcpu_need_to_extend(struct pcpu_chunk *chunk)
 {
         int new_alloc;
-        int *new;
-        size_t size;
 
-        /* has enough? */
         if (chunk->map_alloc >= chunk->map_used + 2)
                 return 0;
 
-        spin_unlock_irqrestore(&pcpu_lock, *flags);
-
         new_alloc = PCPU_DFL_MAP_ALLOC;
         while (new_alloc < chunk->map_used + 2)
                 new_alloc *= 2;
 
-        new = pcpu_mem_alloc(new_alloc * sizeof(new[0]));
-        if (!new) {
-                spin_lock_irqsave(&pcpu_lock, *flags);
+        return new_alloc;
+}
+
+/**
+ * pcpu_extend_area_map - extend area map of a chunk
+ * @chunk: chunk of interest
+ * @new_alloc: new target allocation length of the area map
+ *
+ * Extend area map of @chunk to have @new_alloc entries.
+ *
+ * CONTEXT:
+ * Does GFP_KERNEL allocation.  Grabs and releases pcpu_lock.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
+{
+        int *old = NULL, *new = NULL;
+        size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
+        unsigned long flags;
+
+        new = pcpu_mem_alloc(new_size);
+        if (!new)
                 return -ENOMEM;
-        }
 
-        /*
-         * Acquire pcpu_lock and switch to new area map.  Only free
-         * could have happened inbetween, so map_used couldn't have
-         * grown.
-         */
-        spin_lock_irqsave(&pcpu_lock, *flags);
-        BUG_ON(new_alloc < chunk->map_used + 2);
+        /* acquire pcpu_lock and switch to new area map */
+        spin_lock_irqsave(&pcpu_lock, flags);
+
+        if (new_alloc <= chunk->map_alloc)
+                goto out_unlock;
 
-        size = chunk->map_alloc * sizeof(chunk->map[0]);
-        memcpy(new, chunk->map, size);
+        old_size = chunk->map_alloc * sizeof(chunk->map[0]);
+        memcpy(new, chunk->map, old_size);
 
         /*
          * map_alloc < PCPU_DFL_MAP_ALLOC indicates that the chunk is
          * one of the first chunks and still using static map.
          */
         if (chunk->map_alloc >= PCPU_DFL_MAP_ALLOC)
-                pcpu_mem_free(chunk->map, size);
+                old = chunk->map;
 
         chunk->map_alloc = new_alloc;
         chunk->map = new;
+        new = NULL;
+
+out_unlock:
+        spin_unlock_irqrestore(&pcpu_lock, flags);
+
+        /*
+         * pcpu_mem_free() might end up calling vfree() which uses
+         * IRQ-unsafe lock and thus can't be called under pcpu_lock.
+         */
+        pcpu_mem_free(old, old_size);
+        pcpu_mem_free(new, new_size);
+
         return 0;
 }
 
@@ -1049,7 +1073,7 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved)
         static int warn_limit = 10;
         struct pcpu_chunk *chunk;
         const char *err;
-        int slot, off;
+        int slot, off, new_alloc;
         unsigned long flags;
 
         if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
@@ -1064,14 +1088,25 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved)
         /* serve reserved allocations from the reserved chunk if available */
         if (reserved && pcpu_reserved_chunk) {
                 chunk = pcpu_reserved_chunk;
-                if (size > chunk->contig_hint ||
-                    pcpu_extend_area_map(chunk, &flags) < 0) {
-                        err = "failed to extend area map of reserved chunk";
+
+                if (size > chunk->contig_hint) {
+                        err = "alloc from reserved chunk failed";
                         goto fail_unlock;
                 }
+
+                while ((new_alloc = pcpu_need_to_extend(chunk))) {
+                        spin_unlock_irqrestore(&pcpu_lock, flags);
+                        if (pcpu_extend_area_map(chunk, new_alloc) < 0) {
+                                err = "failed to extend area map of reserved chunk";
+                                goto fail_unlock_mutex;
+                        }
+                        spin_lock_irqsave(&pcpu_lock, flags);
+                }
+
                 off = pcpu_alloc_area(chunk, size, align);
                 if (off >= 0)
                         goto area_found;
+
                 err = "alloc from reserved chunk failed";
                 goto fail_unlock;
         }
@@ -1083,14 +1118,20 @@ restart:
                         if (size > chunk->contig_hint)
                                 continue;
 
-                        switch (pcpu_extend_area_map(chunk, &flags)) {
-                        case 0:
-                                break;
-                        case 1:
-                                goto restart;   /* pcpu_lock dropped, restart */
-                        default:
-                                err = "failed to extend area map";
-                                goto fail_unlock;
+                        new_alloc = pcpu_need_to_extend(chunk);
+                        if (new_alloc) {
+                                spin_unlock_irqrestore(&pcpu_lock, flags);
+                                if (pcpu_extend_area_map(chunk,
+                                                         new_alloc) < 0) {
+                                        err = "failed to extend area map";
+                                        goto fail_unlock_mutex;
+                                }
+                                spin_lock_irqsave(&pcpu_lock, flags);
+                                /*
+                                 * pcpu_lock has been dropped, need to
+                                 * restart cpu_slot list walking.
+                                 */
+                                goto restart;
                         }
 
                         off = pcpu_alloc_area(chunk, size, align);