On Sun, Dec 5, 2021 at 4:07 PM Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > ---- 在 星期四, 2021-12-02 06:47:25 Amir Goldstein <amir73il@xxxxxxxxx> 撰写 ---- > > On Wed, Dec 1, 2021 at 6:24 PM Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > > > > > ---- 在 星期三, 2021-12-01 21:46:10 Jan Kara <jack@xxxxxxx> 撰写 ---- > > > > On Wed 01-12-21 09:19:17, Amir Goldstein wrote: > > > > > On Wed, Dec 1, 2021 at 8:31 AM Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > > > > > So the final solution to handle all the concerns looks like accurately > > > > > > mark overlay inode diry on modification and re-mark dirty only for > > > > > > mmaped file in ->write_inode(). > > > > > > > > > > > > Hi Miklos, Jan > > > > > > > > > > > > Will you agree with new proposal above? > > > > > > > > > > > > > > > > Maybe you can still pull off a simpler version by remarking dirty only > > > > > writably mmapped upper AND inode_is_open_for_write(upper)? > > > > > > > > Well, if inode is writeably mapped, it must be also open for write, doesn't > > > > it? The VMA of the mapping will hold file open. So remarking overlay inode > > > > dirty during writeback while inode_is_open_for_write(upper) looks like > > > > reasonably easy and presumably there won't be that many inodes open for > > > > writing for this to become big overhead? > > > > I think it should be ok and a good tradeoff of complexity vs. performance. > > IMO, mark dirtiness on write is relatively simple, so I think we can mark the > overlayfs inode dirty during real write behavior and only remark writable mmap > unconditionally in ->write_inode(). > If by "on write" you mean on write/copy_file_range/splice_write/... then yes I agree since we have to cover all other mnt_want_write() cases anyway. > > > > > > > > > > > > If I am not mistaken, if you always mark overlay inode dirty on ovl_flush() > > > > > of FMODE_WRITE file, there is nothing that can make upper inode dirty > > > > > after last close (if upper is not mmaped), so one more inode sync should > > > > > be enough. No? > > > > > > > > But we still need to catch other dirtying events like timestamp updates, > > > > truncate(2) etc. to mark overlay inode dirty. Not sure how reliably that > > > > can be done... > > > > > > > > Oh yeh, we have those as well :) > > All those cases should be covered by ovl_copyattr() that updates the > > ovl inode ctime/mtime, so always dirty in ovl_copyattr() should be good. > > Currently ovl_copyattr() does not cover all the cases, so I think we still need to carefully > check all the places of calling mnt_want_write(). > Careful audit is always good, but if we do not have ovl_copyattr() in a call site that should mark inode dirty, then it sounds like a bug, because ovl inode ctime will not get updated. Do you know of any such cases? Thanks, Amir.
