Fix potential data loss and corruption due to Incorrect BIO Chain Handling

[Stephen Zhang]

Ming Lei <ming.lei at redhat.com> 于2025年11月23日周日 21:49写道：
>
> On Sat, Nov 22, 2025 at 03:56:58PM +0100, Andreas Gruenbacher wrote:
> > On Sat, Nov 22, 2025 at 1:07 PM Ming Lei <ming.lei at redhat.com> wrote:
> > > > static void bio_chain_endio(struct bio *bio)
> > > > {
> > > >         bio_endio(__bio_chain_endio(bio));
> > > > }
> > >
> > > bio_chain_endio() never gets called really, which can be thought as `flag`,
> >
> > That's probably where this stops being relevant for the problem
> > reported by Stephen Zhang.
> >
> > > and it should have been defined as `WARN_ON_ONCE(1);` for not confusing people.
> >
> > But shouldn't bio_chain_endio() still be fixed to do the right thing
> > if called directly, or alternatively, just BUG()? Warning and still
> > doing the wrong thing seems a bit bizarre.
>
> IMO calling ->bi_end_io() directly shouldn't be encouraged.
>
> The only in-tree direct call user could be bcache, so is this reported
> issue triggered on bcache?
>
> If bcache can't call bio_endio(), I think it is fine to fix
> bio_chain_endio().
>
> >
> > I also see direct bi_end_io calls in erofs_fileio_ki_complete(),
> > erofs_fscache_bio_endio(), and erofs_fscache_submit_bio(), so those
> > are at least confusing.
>
> All looks FS bio(non-chained), so bio_chain_endio() shouldn't be involved
> in erofs code base.
>

Okay, will add that.

Thanks,
Shida

>
> Thanks,
> Ming
>