Re: AIO read returns negative number for bytes read

[Jan Kara <jack@suse.cz>]

On Tue 17-11-15 14:52:19, Avi Kivity wrote:
> 
> 
> On 11/16/2015 09:27 PM, Jeff Moyer wrote:
> >Hi Avi,
> >
> >Avi Kivity <avi@scylladb.com> writes:
> >
> >>Due to a bug in my program, I initiated a read beyond
> >>eof. Specifically, the file size is 13002 bytes and the read offset is
> >>13312 (0x3400).
> >>
> >>I would expect such a read to return 0 bytes read, but io_getevents
> >>returns -310, which is suspiciously equal to (13002 - 13312).
> >>
> >>I attach a reproducer.
> >>
> >>4.2.5-201.fc22.x86_64
> >>
> >>Are my expectations incorrect, or is this a bug in aio or xfs?
> >Your expectations are correct.  The bug was introduced by commit
> >9fe55eea7e4b4 (Fix race when checking i_size on direct i/o read).  I've
> >CC'd the patch author and linux-fsdevel.  I'm not sure what the right
> >fix is, given that the size checks were removed from the vfs to fix some
> >race condition.  Unfortunately, the commit message doesn't really do a
> >good job of explaining the race.  In order to save others time, here is
> >a good explanation of the problem that commit is meant to fix, along
> >with a reproducer:
> >   http://marc.info/?l=linux-fsdevel&m=138641356614458&w=2
> >
> >Thanks for the great bug report, and sorry I have no solution to
> >proffer.
> >
> 
> Thanks.  I will await a fix with interest.

Can you please post the reproduce here as well? I couldn't easily find it
with google.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR