Re: [PATCH v1 0/5] exfat: fix valid_size handling and locking

[Namjae Jeon]

On Thu, Oct 1, 2026 at 11:53 AM Chi Zhiling <chizhiling@xxxxxxx> wrote:
>
> On 9/30/26 6:01 PM, Namjae Jeon wrote:
> > On Sun, Sep 27, 2026 at 5:04 PM Chi Zhiling <chizhiling@xxxxxxx> wrote:
> >>
> >> From: Chi Zhiling <chizhiling@xxxxxxxxxx>
> >>
> >> valid_size marks the on-disk up-to-date region of an exFAT file. It is
> >> advanced from the write path, from read/zeroing completion, and via
> >> truncate, while it is read without i_rwsem from ->iomap_begin and from bio
> >> completion context. This series fixes several races and stale-data windows
> >> that follow from that split ownership.
> >>
> >> Patches 1-2 are self-contained fixes: an append write may be moved to EOF
> >> by generic_write_checks(), so valid_size must be advanced using the
> >> recalculated position; and exfat_zero_new_range() must mark non-uptodate
> >> pages dirty so the whole page is written back.
> >>
> >> Patches 3-4 are prerequisites for patch 5: truncate now holds the
> >> invalidate lock so it is mutually exclusive with mmap writes, and
> >> valid_size/zeroed_size become atomic so they can be read safely outside
> >> i_rwsem. Patch 5 then takes exfat_page_mkwrite() out from under i_rwsem,
> >> since blocking on the inode lock under mmap_lock could deadlock and its
> >> VM_FAULT_RETRY result is not honored, and advances valid_size under the
> >> folio lock to keep the page cache and valid_size consistent.
> >>
> >> Link: https://lore.kernel.org/exfat/10029d6f-13cc-4d17-a2f9-b093a8339dde@xxxxxxx/T/#t
> >>
> >> Chi Zhiling (5):
> >>    exfat: advance valid_size to EOF for append writes
> >>    exfat: dirty all new pages when extending valid_size
> >>    exfat: hold the invalidate lock while truncating
> >>    exfat: make valid_size and zeroed_size atomic
> >>    exfat: use folio lock to protect valid_size
> > Could you check the review comments from Sashiko ?
> >
> > https://sashiko.dev/#/patchset/20260927080305.831641-1-chizhiling%40163.com
>
> Okay, I’ll take a close look at this review comment.
>
> I also noticed that the comment mentions that concurrent DIO and page
> faults may lead to data corruption. I believe this is a long-standing
> issue, and I don’t currently have a good way to fix it.
Okay, I'll take a look at that. Will you send v2 patchset soon?
Thanks!