xfs: preserve i_rdev when recycling a reclaimable inode

Commit 66f364649d870 ("xfs: remove if_rdev") moved storing of rdev
value for special inodes to VFS inodes, but forgot to preserve the
value of i_rdev when recycling a reclaimable xfs_inode.

This was detected by xfstest overlay/017 with inodex=on mount option
and xfs base fs. The test does a lookup of overlay chardev and blockdev
right after drop caches.

Overlayfs inodes hold a reference on underlying xfs inodes when mount
option index=on is configured. If drop caches reclaim xfs inodes, before
it relclaims overlayfs inodes, that can sometimes leave a reclaimable xfs
inode and that test hits that case quite often.

When that happens, the xfs inode cache remains broken (zere i_rdev)
until the next cycle mount or drop caches.

Fixes: 66f364649d870 ("xfs: remove if_rdev")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_icache.c

@@ -295,6 +295,7 @@ xfs_reinit_inode(
 	uint32_t	generation = inode->i_generation;
 	uint64_t	version = inode->i_version;
 	umode_t		mode = inode->i_mode;
+	dev_t		dev = inode->i_rdev;
 
 	error = inode_init_always(mp->m_super, inode);
 
@@ -302,6 +303,7 @@ xfs_reinit_inode(
 	inode->i_generation = generation;
 	inode->i_version = version;
 	inode->i_mode = mode;
+	inode->i_rdev = dev;
 	return error;
 }