[PATCH 07/12] xfs: take XFS_MMAPLOCK_EXCL xfs_file_write_zero_eof

[Christoph Hellwig <hch@lst.de>]

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 acrually 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>
---
 fs/xfs/xfs_file.c  | 8 +++++++-
 fs/xfs/xfs_iomap.c | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index a30fda1985e6af..37dc26f51ace65 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -357,6 +357,7 @@ 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
@@ -404,7 +405,12 @@ 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;
 }
 
 /*
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 1e11f48814c0d0..3c98d82c0ad0dc 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1435,6 +1435,8 @@ 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);
-- 
2.45.2