Re: [PATCH v2 2/3] btrfs: zoned: fix compressed writes

[David Sterba <dsterba@suse.cz>]

On Mon, May 24, 2021 at 09:04:40PM +0800, Qu Wenruo wrote:
> > This is the interesting part, it means we are just one sector beyond the
> > stripe boundary.
> > Definitely a sign of changed bio submission timing.
> >
> > Just like the code:
> >
> > +        if (pg_index == 0 && use_append)
> > +            len = bio_add_zone_append_page(bio, page, PAGE_SIZE, 0);
> > +        else
> > +            len = bio_add_page(bio, page, PAGE_SIZE, 0);
> > +
> >           page->mapping = NULL;
> > -        if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) <
> > -            PAGE_SIZE) {
> > +        if (submit || len < PAGE_SIZE) {
> >
> > The code has changed the timing of bio_add_page().
> >
> > Previously, if we have submit == true, we won't even try to call
> > bio_add_page().
> >
> > But now, we will add the page even we're already at the stripe boundary,
> > thus it causes the extra sector being added to bio, and crosses stripe
> > boundary.
> >
> > This part is already super tricky, thus I refactored
> > submit_extent_page() to do a better job at stripe boundary calculation.
> 
> BTW, I can also reproduce the problem in btrfs/027 using the latest
> misc-next branch.
> 
> Thus to workaround the problem, I'm using the following diff, feel free
> to fold in to the offending patch.

The patch is now in master so we'll need a proper fix.