On Sun, Apr 9, 2023 at 2:18 PM Andres Freund <andres@anarazel.de> wrote:
> On 2023-04-09 13:55:33 +1200, Thomas Munro wrote:
> > I think that particular thing might relate to modifications of the
> > user buffer while a write is in progress (breaking btrfs's internal
> > checksums). I don't think we should ever do that ourselves (not least
> > because it'd break our own checksums). We lock the page during the
> > write so no one can do that, and then we sleep in a synchronous
> > syscall.
>
> Oh, but we actually *do* modify pages while IO is going on. I wonder if you
> hit the jack pot here. The content lock doesn't prevent hint bit
> writes. That's why we copy the page to temporary memory when computing
> checksums.
More like the jackpot hit me.
Woo, I can now reproduce this locally on a loop filesystem.
Previously I had missed a step, the parallel worker seems to be
necessary. More soon.
