diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 8276cc282decb466c360c6d6e1c8a9f31ee73c9d..a975b4147e9179fe6bf3bd1917b48ec8a031110b 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -109,6 +109,7 @@ struct msdos_inode_info {
 	int i_attrs;		/* unused attribute bits */
 	loff_t i_pos;		/* on-disk position of directory entry or 0 */
 	struct hlist_node i_fat_hash;	/* hash by i_location */
+	struct rw_semaphore truncate_lock; /* protect bmap against truncate */
 	struct inode vfs_inode;
 };
 
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 7018e1d8902dee6c4b38f7247a38e9315cba27f5..a4a3a3c06436d79293cc349187f616a3e6e79bd2 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -429,8 +429,10 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
 	}
 
 	if (attr->ia_valid & ATTR_SIZE) {
+		down_write(&MSDOS_I(inode)->truncate_lock);
 		truncate_setsize(inode, attr->ia_size);
 		fat_truncate_blocks(inode, attr->ia_size);
+		up_write(&MSDOS_I(inode)->truncate_lock);
 	}
 
 	setattr_copy(inode, attr);
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index cb8d8391ac0bb67c815e45b90127f89a3f6368f5..3decce46c38f867b46ea77c0bba4d547711aba07 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -224,9 +224,9 @@ static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
 	sector_t blocknr;
 
 	/* fat_get_cluster() assumes the requested blocknr isn't truncated. */
-	down_read(&mapping->host->i_alloc_sem);
+	down_read(&MSDOS_I(mapping->host)->truncate_lock);
 	blocknr = generic_block_bmap(mapping, block, fat_get_block);
-	up_read(&mapping->host->i_alloc_sem);
+	up_read(&MSDOS_I(mapping->host)->truncate_lock);
 
 	return blocknr;
 }
@@ -510,6 +510,8 @@ static struct inode *fat_alloc_inode(struct super_block *sb)
 	ei = kmem_cache_alloc(fat_inode_cachep, GFP_NOFS);
 	if (!ei)
 		return NULL;
+
+	init_rwsem(&ei->truncate_lock);
 	return &ei->vfs_inode;
 }