btrfs: fix race in reada

When inserting into the radix tree returns EEXIST, get the existing
entry without giving up the spinlock in between.
There was a race for both the zones trees and the extent tree.

Signed-off-by: Arne Jansen <sensille@gmx.net>

2 files changed, 23 insertions, 20 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a682c267576d..98ee5a51aa29 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4332,7 +4332,13 @@ static int btrfs_real_readdir(struct file *filp, void *dirent,
                         }
 no_dentry:
                         /* is this a reference to our own snapshot? If so
-                         * skip it
+                         * skip it.
+                         *
+                         * In contrast to old kernels, we insert the snapshot's
+                         * dir item and dir index after it has been created, so
+                         * we won't find a reference to our own snapshot. We
+                         * still keep the following code for backward
+                         * compatibility.
                          */
                         if (location.type == BTRFS_ROOT_ITEM_KEY &&
                             location.objectid == root->root_key.objectid) {
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index dc5d33146fdb..8dec650099c8 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -250,14 +250,12 @@ static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info,
                                           struct btrfs_bio *bbio)
 {
         int ret;
-        int looped = 0;
         struct reada_zone *zone;
         struct btrfs_block_group_cache *cache = NULL;
         u64 start;
         u64 end;
         int i;
 
-again:
         zone = NULL;
         spin_lock(&fs_info->reada_lock);
         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
@@ -274,9 +272,6 @@ again:
                 spin_unlock(&fs_info->reada_lock);
         }
 
-        if (looped)
-                return NULL;
-
         cache = btrfs_lookup_block_group(fs_info, logical);
         if (!cache)
                 return NULL;
@@ -307,13 +302,15 @@ again:
         ret = radix_tree_insert(&dev->reada_zones,
                                 (unsigned long)(zone->end >> PAGE_CACHE_SHIFT),
                                 zone);
-        spin_unlock(&fs_info->reada_lock);
 
-        if (ret) {
+        if (ret == -EEXIST) {
                 kfree(zone);
-                looped = 1;
-                goto again;
+                ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
+                                             logical >> PAGE_CACHE_SHIFT, 1);
+                if (ret == 1)
+                        kref_get(&zone->refcnt);
         }
+        spin_unlock(&fs_info->reada_lock);
 
         return zone;
 }
@@ -323,8 +320,8 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
                                               struct btrfs_key *top, int level)
 {
         int ret;
-        int looped = 0;
         struct reada_extent *re = NULL;
+        struct reada_extent *re_exist = NULL;
         struct btrfs_fs_info *fs_info = root->fs_info;
         struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
         struct btrfs_bio *bbio = NULL;
@@ -335,14 +332,13 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
         int i;
         unsigned long index = logical >> PAGE_CACHE_SHIFT;
 
-again:
         spin_lock(&fs_info->reada_lock);
         re = radix_tree_lookup(&fs_info->reada_tree, index);
         if (re)
                 kref_get(&re->refcnt);
         spin_unlock(&fs_info->reada_lock);
 
-        if (re || looped)
+        if (re)
                 return re;
 
         re = kzalloc(sizeof(*re), GFP_NOFS);
@@ -398,12 +394,15 @@ again:
         /* insert extent in reada_tree + all per-device trees, all or nothing */
         spin_lock(&fs_info->reada_lock);
         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
+        if (ret == -EEXIST) {
+                re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
+                BUG_ON(!re_exist);
+                kref_get(&re_exist->refcnt);
+                spin_unlock(&fs_info->reada_lock);
+                goto error;
+        }
         if (ret) {
                 spin_unlock(&fs_info->reada_lock);
-                if (ret != -ENOMEM) {
-                        /* someone inserted the extent in the meantime */
-                        looped = 1;
-                }
                 goto error;
         }
         for (i = 0; i < nzones; ++i) {
@@ -450,9 +449,7 @@ error:
         }
         kfree(bbio);
         kfree(re);
-        if (looped)
-                goto again;
-        return NULL;
+        return re_exist;
 }
 
 static void reada_kref_dummy(struct kref *kr)