Btrfs: add missing read locks in backref.c

iref_to_path and iterate_irefs both increment the eb's refcount to use it
after releasing the path. Both depend on consistent data remaining in the
extent buffer and need a read lock to protect it.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 15 insertions, 2 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index fb56bcc80377..bcec06750232 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -22,6 +22,7 @@
 #include "ulist.h"
 #include "transaction.h"
 #include "delayed-ref.h"
+#include "locking.h"
 
 /*
  * this structure records all encountered refs on the way up to the root
@@ -893,18 +894,22 @@ static char *iref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
         s64 bytes_left = size - 1;
         struct extent_buffer *eb = eb_in;
         struct btrfs_key found_key;
+        int leave_spinning = path->leave_spinning;
 
         if (bytes_left >= 0)
                 dest[bytes_left] = '\0';
 
+        path->leave_spinning = 1;
         while (1) {
                 len = btrfs_inode_ref_name_len(eb, iref);
                 bytes_left -= len;
                 if (bytes_left >= 0)
                         read_extent_buffer(eb, dest + bytes_left,
                                                 (unsigned long)(iref + 1), len);
-                if (eb != eb_in)
+                if (eb != eb_in) {
+                        btrfs_tree_read_unlock_blocking(eb);
                         free_extent_buffer(eb);
+                }
                 ret = inode_ref_info(parent, 0, fs_root, path, &found_key);
                 if (ret > 0)
                         ret = -ENOENT;
@@ -919,8 +924,11 @@ static char *iref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
                 slot = path->slots[0];
                 eb = path->nodes[0];
                 /* make sure we can use eb after releasing the path */
-                if (eb != eb_in)
+                if (eb != eb_in) {
                         atomic_inc(&eb->refs);
+                        btrfs_tree_read_lock(eb);
+                        btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+                }
                 btrfs_release_path(path);
 
                 iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
@@ -931,6 +939,7 @@ static char *iref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
         }
 
         btrfs_release_path(path);
+        path->leave_spinning = leave_spinning;
 
         if (ret)
                 return ERR_PTR(ret);
@@ -1260,6 +1269,7 @@ static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
         struct btrfs_key found_key;
 
         while (!ret) {
+                path->leave_spinning = 1;
                 ret = inode_ref_info(inum, parent ? parent+1 : 0, fs_root, path,
                                         &found_key);
                 if (ret < 0)
@@ -1275,6 +1285,8 @@ static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
                 eb = path->nodes[0];
                 /* make sure we can use eb after releasing the path */
                 atomic_inc(&eb->refs);
+                btrfs_tree_read_lock(eb);
+                btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
                 btrfs_release_path(path);
 
                 item = btrfs_item_nr(eb, slot);
@@ -1293,6 +1305,7 @@ static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
                         len = sizeof(*iref) + name_len;
                         iref = (struct btrfs_inode_ref *)((char *)iref + len);
                 }
+                btrfs_tree_read_unlock_blocking(eb);
                 free_extent_buffer(eb);
         }