[B][PATCH 5/5] ext4: fix mmap write protection for data=journal mode

[Mauricio Faria de Oliveira]

From: Jan Kara <jack at suse.cz>

BugLink: https://bugs.launchpad.net/bugs/1847340

Commit afb585a97f81 "ext4: data=journal: write-protect pages on
j_submit_inode_data_buffers()") added calls ext4_jbd2_inode_add_write()
to track inode ranges whose mappings need to get write-protected during
transaction commits.  However the added calls use wrong start of a range
(0 instead of page offset) and so write protection is not necessarily
effective.  Use correct range start to fix the problem.

Fixes: afb585a97f81 ("ext4: data=journal: write-protect pages on j_submit_inode_data_buffers()")
Signed-off-by: Jan Kara <jack at suse.cz>
Link: https://lore.kernel.org/r/20201027132751.29858-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
(cherry picked from commit b5b18160a3e7a9f55e3528d77051670cca6d9314)
Signed-off-by: Mauricio Faria de Oliveira <mfo at canonical.com>
---
 fs/ext4/inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fa0d77dade2c..348f941c8531 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2066,7 +2066,7 @@ static int __ext4_journalled_writepage(struct page *page,
 	}
 	if (ret == 0)
 		ret = err;
-	err = ext4_jbd2_inode_add_write(handle, inode, 0, len);
+	err = ext4_jbd2_inode_add_write(handle, inode, page_offset(page), len);
 	if (ret == 0)
 		ret = err;
 	EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
@@ -6324,7 +6324,8 @@ int ext4_page_mkwrite(struct vm_fault *vmf)
 			if (ext4_walk_page_buffers(handle, page_buffers(page),
 					0, len, NULL, write_end_fn))
 				goto out_error;
-			if (ext4_jbd2_inode_add_write(handle, inode, 0, len))
+			if (ext4_jbd2_inode_add_write(handle, inode,
+						      page_offset(page), len))
 				goto out_error;
 			ext4_set_inode_state(inode, EXT4_STATE_JDATA);
 			ret = 0; // ensure return is VM_FAULT_LOCKED.
-- 
2.30.2