Btrfs: use kmalloc instead of stack for backref_ctx

Make sure to never get in trouble due to the backref_ctx
which was on the stack before.

Commit is a result of Arne's review.

Signed-off-by: Alexander Block <ablock84@googlemail.com>

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index a25be0c1a6b9d2ed5ee39f4b06a98e88aecbd018..36711123bdcf071a8db2a9e5d75396207d884b20 100644 (file)
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -1149,7 +1149,7 @@ static int find_extent_clone(struct send_ctx *sctx,
        u64 extent_item_pos;
        struct btrfs_file_extent_item *fi;
        struct extent_buffer *eb = path->nodes[0];
-       struct backref_ctx backref_ctx;
+       struct backref_ctx *backref_ctx = NULL;
        struct clone_root *cur_clone_root;
        struct btrfs_key found_key;
        struct btrfs_path *tmp_path;
@@ -1159,6 +1159,12 @@ static int find_extent_clone(struct send_ctx *sctx,
        if (!tmp_path)
                return -ENOMEM;
 
+       backref_ctx = kmalloc(sizeof(*backref_ctx), GFP_NOFS);
+       if (!backref_ctx) {
+               ret = -ENOMEM;
+               goto out;
+       }
+
        if (data_offset >= ino_size) {
                /*
                 * There may be extents that lie behind the file's size.
@@ -1206,12 +1212,12 @@ static int find_extent_clone(struct send_ctx *sctx,
                cur_clone_root->found_refs = 0;
        }
 
-       backref_ctx.sctx = sctx;
-       backref_ctx.found = 0;
-       backref_ctx.cur_objectid = ino;
-       backref_ctx.cur_offset = data_offset;
-       backref_ctx.found_itself = 0;
-       backref_ctx.extent_len = num_bytes;
+       backref_ctx->sctx = sctx;
+       backref_ctx->found = 0;
+       backref_ctx->cur_objectid = ino;
+       backref_ctx->cur_offset = data_offset;
+       backref_ctx->found_itself = 0;
+       backref_ctx->extent_len = num_bytes;
 
        /*
         * The last extent of a file may be too large due to page alignment.
@@ -1219,7 +1225,7 @@ static int find_extent_clone(struct send_ctx *sctx,
         * __iterate_backrefs work.
         */
        if (data_offset + num_bytes >= ino_size)
-               backref_ctx.extent_len = ino_size - data_offset;
+               backref_ctx->extent_len = ino_size - data_offset;
 
        /*
         * Now collect all backrefs.
@@ -1227,11 +1233,11 @@ static int find_extent_clone(struct send_ctx *sctx,
        extent_item_pos = logical - found_key.objectid;
        ret = iterate_extent_inodes(sctx->send_root->fs_info,
                                        found_key.objectid, extent_item_pos, 1,
-                                       __iterate_backrefs, &backref_ctx);
+                                       __iterate_backrefs, backref_ctx);
        if (ret < 0)
                goto out;
 
-       if (!backref_ctx.found_itself) {
+       if (!backref_ctx->found_itself) {
                /* found a bug in backref code? */
                ret = -EIO;
                printk(KERN_ERR "btrfs: ERROR did not find backref in "
@@ -1246,7 +1252,7 @@ verbose_printk(KERN_DEBUG "btrfs: find_extent_clone: data_offset=%llu, "
                "num_bytes=%llu, logical=%llu\n",
                data_offset, ino, num_bytes, logical);
 
-       if (!backref_ctx.found)
+       if (!backref_ctx->found)
                verbose_printk("btrfs:    no clones found\n");
 
        cur_clone_root = NULL;
@@ -1271,6 +1277,7 @@ verbose_printk(KERN_DEBUG "btrfs: find_extent_clone: data_offset=%llu, "
 
 out:
        btrfs_free_path(tmp_path);
+       kfree(backref_ctx);
        return ret;
 }