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>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a682c267576db43f1406ca9da0694b64fa95879e..98ee5a51aa29b4497b1c8e36ad82bb1bf24fcc8e 100644 (file)
--- 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 dc5d33146fdbb9f4fb3cf899d78a97ca361b6ac8..8dec650099c8a3d924e778c4b6aa3e89b2c945fb 100644 (file)
--- 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)