fs/hfsplus/extents.c: fix concurrent acess of alloc_blocks

Concurrent access to alloc_blocks in hfsplus_inode_info() is protected
by extents_lock mutex.  This patch fixes two instances where
alloc_blocks modification was not protected with this lock.

This fixes possible allocation bitmap corruption in race conditions
while extending and truncating files.

[akpm@linux-foundation.org: take extents_lock before taking a copy of ->alloc_blocks]
[akpm@linux-foundation.org: remove now-unused label `out']
Signed-off-by: Sougata Santra <sougata@tuxera.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfsplus/extents.c

@@ -496,11 +496,13 @@ int hfsplus_file_extend(struct inode *inode)
 			goto insert_extent;
 	}
 out:
-	mutex_unlock(&hip->extents_lock);
 	if (!res) {
 		hip->alloc_blocks += len;
+		mutex_unlock(&hip->extents_lock);
 		hfsplus_mark_inode_dirty(inode, HFSPLUS_I_ALLOC_DIRTY);
+		return 0;
 	}
+	mutex_unlock(&hip->extents_lock);
 	return res;
 
 insert_extent:
@@ -554,11 +556,13 @@ void hfsplus_file_truncate(struct inode *inode)
 
 	blk_cnt = (inode->i_size + HFSPLUS_SB(sb)->alloc_blksz - 1) >>
 			HFSPLUS_SB(sb)->alloc_blksz_shift;
+
+	mutex_lock(&hip->extents_lock);
+
 	alloc_cnt = hip->alloc_blocks;
 	if (blk_cnt == alloc_cnt)
-		goto out;
+		goto out_unlock;
 
-	mutex_lock(&hip->extents_lock);
 	res = hfs_find_init(HFSPLUS_SB(sb)->ext_tree, &fd);
 	if (res) {
 		mutex_unlock(&hip->extents_lock);
@@ -590,10 +594,10 @@ void hfsplus_file_truncate(struct inode *inode)
 		hfs_brec_remove(&fd);
 	}
 	hfs_find_exit(&fd);
-	mutex_unlock(&hip->extents_lock);
 
 	hip->alloc_blocks = blk_cnt;
-out:
+out_unlock:
+	mutex_unlock(&hip->extents_lock);
 	hip->phys_size = inode->i_size;
 	hip->fs_blocks = (inode->i_size + sb->s_blocksize - 1) >>
 		sb->s_blocksize_bits;