ext4: teach ext4_ext_find_extent() to free path on error

Right now, there are a places where it is all to easy to leak memory
on an error path, via a usage like this:

	struct ext4_ext_path *path = NULL

	while (...) {
		...
		path = ext4_ext_find_extent(inode, block, path, 0);
		if (IS_ERR(path)) {
			/* oops, if path was non-NULL before the call to
			   ext4_ext_find_extent, we've leaked it!  :-(  */
			...
			return PTR_ERR(path);
		}
		...
	}

Unfortunately, there some code paths where we are doing the following
instead:

	path = ext4_ext_find_extent(inode, block, orig_path, 0);

and where it's important that we _not_ free orig_path in the case
where ext4_ext_find_extent() returns an error.

So change the function signature of ext4_ext_find_extent() so that it
takes a struct ext4_ext_path ** for its third argument, and by
default, on an error, it will free the struct ext4_ext_path, and then
zero out the struct ext4_ext_path * pointer.  In order to avoid
causing problems, we add a flag EXT4_EX_NOFREE_ON_ERR which causes
ext4_ext_find_extent() to use the original behavior of forcing the
caller to deal with freeing the original path pointer on the error
case.

The goal is to get rid of EXT4_EX_NOFREE_ON_ERR entirely, but this
allows for a gentle transition and makes the patches easier to verify.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 550b4f9..696e51a 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -582,6 +582,7 @@ enum {
  */
 #define EXT4_EX_NOCACHE                                0x0800
 #define EXT4_EX_FORCE_CACHE                    0x1000
+#define EXT4_EX_NOFREE_ON_ERR                  0x2000
 
 /*
  * Flags used by ext4_free_blocks
@@ -2733,7 +2734,7 @@ extern int ext4_ext_insert_extent(handle_t *, struct inode *,
                                  struct ext4_ext_path *,
                                  struct ext4_extent *, int);
 extern struct ext4_ext_path *ext4_ext_find_extent(struct inode *, ext4_lblk_t,
-                                                 struct ext4_ext_path *,
+                                                 struct ext4_ext_path **,
                                                  int flags);
 extern void ext4_ext_drop_refs(struct ext4_ext_path *);
 extern int ext4_ext_check_inode(struct inode *inode);

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index bf205f7..0ced78c 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -855,11 +855,13 @@ int ext4_ext_tree_init(handle_t *handle, struct inode *inode)
 
 struct ext4_ext_path *
 ext4_ext_find_extent(struct inode *inode, ext4_lblk_t block,
-                    struct ext4_ext_path *path, int flags)
+                    struct ext4_ext_path **orig_path, int flags)
 {
        struct ext4_extent_header *eh;
        struct buffer_head *bh;
-       short int depth, i, ppos = 0, alloc = 0;
+       struct ext4_ext_path *path = orig_path ? *orig_path : NULL;
+       short int depth, i, ppos = 0;
+       short free_on_err = (flags & EXT4_EX_NOFREE_ON_ERR) == 0;
        int ret;
 
        eh = ext_inode_hdr(inode);
@@ -871,7 +873,7 @@ ext4_ext_find_extent(struct inode *inode, ext4_lblk_t block,
                                GFP_NOFS);
                if (unlikely(!path))
                        return ERR_PTR(-ENOMEM);
-               alloc = 1;
+               free_on_err = 1;
        }
        path[0].p_hdr = eh;
        path[0].p_bh = NULL;
@@ -923,8 +925,11 @@ ext4_ext_find_extent(struct inode *inode, ext4_lblk_t block,
 
 err:
        ext4_ext_drop_refs(path);
-       if (alloc)
+       if (free_on_err) {
                kfree(path);
+               if (orig_path)
+                       *orig_path = NULL;
+       }
        return ERR_PTR(ret);
 }
 
@@ -1356,7 +1361,7 @@ repeat:
                ext4_ext_drop_refs(path);
                path = ext4_ext_find_extent(inode,
                                    (ext4_lblk_t)le32_to_cpu(newext->ee_block),
-                                   path, gb_flags);
+                                   &path, gb_flags | EXT4_EX_NOFREE_ON_ERR);
                if (IS_ERR(path))
                        err = PTR_ERR(path);
        } else {
@@ -1369,7 +1374,7 @@ repeat:
                ext4_ext_drop_refs(path);
                path = ext4_ext_find_extent(inode,
                                   (ext4_lblk_t)le32_to_cpu(newext->ee_block),
-                                   path, gb_flags);
+                                   &path, gb_flags | EXT4_EX_NOFREE_ON_ERR);
                if (IS_ERR(path)) {
                        err = PTR_ERR(path);
                        goto out;
@@ -2152,7 +2157,7 @@ static int ext4_fill_fiemap_extents(struct inode *inode,
                        path = NULL;
                }
 
-               path = ext4_ext_find_extent(inode, block, path, 0);
+               path = ext4_ext_find_extent(inode, block, &path, 0);
                if (IS_ERR(path)) {
                        up_read(&EXT4_I(inode)->i_data_sem);
                        err = PTR_ERR(path);
@@ -3313,7 +3318,8 @@ static int ext4_split_extent(handle_t *handle,
         * result in split of original leaf or extent zeroout.
         */
        ext4_ext_drop_refs(path);
-       path = ext4_ext_find_extent(inode, map->m_lblk, path, 0);
+       path = ext4_ext_find_extent(inode, map->m_lblk, &path,
+                                   EXT4_EX_NOFREE_ON_ERR);
        if (IS_ERR(path))
                return PTR_ERR(path);
        depth = ext_depth(inode);
@@ -3697,7 +3703,8 @@ static int ext4_convert_initialized_extents(handle_t *handle,
                if (err < 0)
                        goto out;
                ext4_ext_drop_refs(path);
-               path = ext4_ext_find_extent(inode, map->m_lblk, path, 0);
+               path = ext4_ext_find_extent(inode, map->m_lblk, &path,
+                                           EXT4_EX_NOFREE_ON_ERR);
                if (IS_ERR(path)) {
                        err = PTR_ERR(path);
                        goto out;
@@ -3769,7 +3776,8 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle,
                if (err < 0)
                        goto out;
                ext4_ext_drop_refs(path);
-               path = ext4_ext_find_extent(inode, map->m_lblk, path, 0);
+               path = ext4_ext_find_extent(inode, map->m_lblk, &path,
+                                           EXT4_EX_NOFREE_ON_ERR);
                if (IS_ERR(path)) {
                        err = PTR_ERR(path);
                        goto out;

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index c8f895b..5e2465a 100644 (file)
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -37,7 +37,7 @@ get_ext_path(struct inode *inode, ext4_lblk_t lblock,
        int ret = 0;
        struct ext4_ext_path *path;
 
-       path = ext4_ext_find_extent(inode, lblock, *orig_path, EXT4_EX_NOCACHE);
+       path = ext4_ext_find_extent(inode, lblock, orig_path, EXT4_EX_NOCACHE);
        if (IS_ERR(path))
                ret = PTR_ERR(path);
        else if (path[ext_depth(inode)].p_ext == NULL)