On Mon 20-03-23 20:49:07, Zhihao Cheng wrote:
[...]
BTW, I want send another patch as follows:
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..570a687ae847 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
return ext4_write_inline_data_end(inode, pos, len, copied,
page);
start = pos & (PAGE_SIZE - 1);
- end = start + copied - 1;
+ end = start + (copied ? copied - 1 : copied);
/*
* Since we are holding inode lock, we are sure i_disksize <=
@@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
* ext4_da_write_inline_data_end().
*/
new_i_size = pos + copied;
- if (copied && new_i_size > inode->i_size &&
+ if (new_i_size > inode->i_size &&
ext4_da_should_update_i_disksize(page, end))
ext4_update_i_disksize(inode, new_i_size);
This modification handle unconsistent i_size and i_disksize imported by
ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
Paritially written may display a fake inode size for user, for example:
i_disksize=1
generic_perform_write
copied = iov_iter_copy_from_user_atomic(len) // copied = 0
ext4_da_write_end // skip updating i_disksize
generic_write_end
if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
i_size_write(inode, pos + copied); // i_size = 10
}
0 1 10 4096
|_|_______|_________..._____|
| |
i_size pos
Now, user see the i_size is 10 (i_disksize is still 1). After inode
destroyed, user will get the i_size is 1 read from disk.
OK, but shouldn't we rather change generic_write_end() to not increase
i_size if no write happened? Because that is what seems somewhat
problematic...
Honza
After looking through some code, I find some other places have similar
problem:
1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end().
2. The iommap framework, i_size is updated even copied is zero.
3. ubifs_write_end, i_size is updated even copied is zero.
It seems that fixing all places is not an easy work.
Well, yeah, probably not trivial but still desirable ;). Will you look into
that?
Honza
I'am happy to investigate it, maybe it will take some time, and I'm also
glad to help review code if somebody come up a solution firstly.
