xfs: take XFS_MMAPLOCK_EXCL xfs_file_write_zero_eof

xfs_file_write_zero_eof is the only caller of xfs_zero_range that does
not take XFS_MMAPLOCK_EXCL (aka the invalidate lock).  Currently that
is actually the right thing, as an error in the iomap zeroing code will
also take the invalidate_lock to clean up, but to fix that deadlock we
need a consistent locking pattern first.

The only extra thing that XFS_MMAPLOCK_EXCL will lock out are read
pagefaults, which isn't really needed here, but also not actively
harmful.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

fs/xfs/xfs_file.c

@@ -364,6 +364,7 @@ xfs_file_write_zero_eof(
 {
 	struct xfs_inode	*ip = XFS_I(iocb->ki_filp->f_mapping->host);
 	loff_t			isize;
+	int			error;
 
 	/*
 	 * We need to serialise against EOF updates that occur in IO completions
@@ -411,7 +412,12 @@ xfs_file_write_zero_eof(
 	}
 
 	trace_xfs_zero_eof(ip, isize, iocb->ki_pos - isize);
-	return xfs_zero_range(ip, isize, iocb->ki_pos - isize, NULL);
+
+	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
+	error = xfs_zero_range(ip, isize, iocb->ki_pos - isize, NULL);
+	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
+
+	return error;
 }
 
 /*

fs/xfs/xfs_iomap.c

@@ -1449,6 +1449,8 @@ xfs_zero_range(
 {
 	struct inode		*inode = VFS_I(ip);
 
+	xfs_assert_ilocked(ip, XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL);
+
 	if (IS_DAX(inode))
 		return dax_zero_range(inode, pos, len, did_zero,
 				      &xfs_dax_write_iomap_ops);