Re: read corruption with qemu master io_uring engine / linux master / btrfs(?)

[Filipe Manana <fdmanana@kernel.org>]

On Fri, Jul 01, 2022 at 09:45:04AM +0100, Filipe Manana wrote:
> On Fri, Jul 01, 2022 at 10:25:58AM +0900, Dominique MARTINET wrote:
> > Filipe Manana wrote on Thu, Jun 30, 2022 at 04:10:38PM +0100:
> > > This may prevent the short reads (not tested yet):
> > > 
> > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > > index 7a54f964ff37..42fb56ed0021 100644
> > > --- a/fs/btrfs/inode.c
> > > +++ b/fs/btrfs/inode.c
> > > @@ -7684,7 +7684,7 @@ static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start,
> > >         if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) ||
> > >             em->block_start == EXTENT_MAP_INLINE) {
> > >                 free_extent_map(em);
> > > -               ret = -ENOTBLK;
> > > +               ret = (flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOTBLK;
> > >                 goto unlock_err;
> > >         }
> > >  
> > > Can you give it a try?
> > 
> > This appears to do the trick!
> > I've also removed the first patch and still cannot see any short reads,
> > so this would be enough on its own for my case.
> 
> Great.
> 
> After my last reply, I retried your reproducer (and qemu image file) on a fs
> mounted with -o compress-force=zstd and was able to trigger the short reads
> in less than a minute.
> 
> Witht that patch I can no longer trigger the short reads too (after running
> the reproducer for about 2 hours).
> 
> I'll give it some more testing here along with other minor fixes I have for
> other scenarios. I'll submit a patchset, with this fix included, on monday.

In the meanwhile, I've left the patches staging here:

https://git.kernel.org/pub/scm/linux/kernel/git/fdmanana/linux.git/log/?h=dio_fixes

> 
> I'll add your Tested-by tag for this specific patch.
> 
> Thanks for all the testing and the reproducer!
> 
> 
> > 
> > -- 
> > Dominique