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>

1 files changed, 18 insertions, 11 deletions

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index a25be0c1a6b9..36711123bdcf 100644
--- 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;
 }