Re: [Bug 3317] New: Kernel oops in aio_complete while running AIOapplication

[badari]

Daniel,

aio_complete() gets called only when we are done with this dio.
Other calls to finished_one_bio() should be fine. dio->result
should have the return value we want to send back. The fix
I made is to call aio_complete() only if we have something to
report back.

One problem is, dio->result gets updated for IO errors bur
doesn't get updated for errors from get_user_pages().  Things
should be fine, but I am not really comfortable retruning half
errors thro aio_complete() and other half thro return value
of do_direct_IO(). I guess its okay, since some of the IO errors
can happen only after we submit the bio.

Thanks,
Badari

Daniel McNeil wrote:

> On Fri, 2004-09-03 at 08:52, Badari Pulavarty wrote:
>  
>
> > On Tue, 2004-08-31 at 08:18, Andrew Morton wrote:
> >    
> >
> > > Begin forwarded message:
> > >
> > > Date: Tue, 31 Aug 2004 06:15:18 -0700
> > > From: bugme-daemon@xxxxxxxx
> > > To: bugme-new@xxxxxxxxxxxxxx
> > > Subject: [Bugme-new] [Bug 3317] New: Kernel oops in aio_complete while running AIO application
> > >
> > >
> > > http://bugme.osdl.org/show_bug.cgi?id=3317
> > >
> > >      
> > Hi Andrew,
> >
> > I debugged this some more. Here is whats happening:
> >
> > The test program used program text address as buffer to do the READ to.
> > DIO get_user_pages() returned EFAULT. We called finished_one_bio()
> > as part of dropping the ref. to dio. It called aio_complete().
> > do_direct_IO() returned EFAULT to the caller. aio_run_iocb() expects
> > to see EIOCBQUEUED/RETRY, otherwise it calls aio_complete() with the
> > "ret" value. This is where the second aio_complete() is coming from.
> > So we cleanup "req" and on the next de-ref we get OOPS.
> >
> > The problem here is, finished_one_bio() shouldn't call aio_complete()
> > since no work has been done. I have a fix for this - can you verify this
> > ? I am not really comfortable with this "tweaking". (I am not really
> > sure about IO errors like EIO etc. - if they can lead to calling
> > aio_complete() twice)
> >
> >
> > Fix is to call aio_complete() ONLY if there is something to report.
> > Note the we don't update dio->result with any error codes from
> > get_user_pages(), they just passed as "ret" value from do_direct_IO().
> >
> > Thanks,
> > Badari
> >    
>
> Badari,
>
> This does fix the problem when running on my system (ext3).
>
> One question, finished_one_bio() is called in 3 places,
> are you sure the other places won't be harmed by this
> change?
>
> I'm also looking over the code and will let you know if
> I see any problems.
>
> Daniel
>
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>  

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