end_request error procedure in 2.5?

end_request error procedure in 2.5?

[Peter T. Breuer]

Can someone tell me why this block end_request routine works fine with a
request that isn't errored, but locks the machine a milisecond or two
later if the request is marked for erroring?

call as 

 end_request( req, (req->errors == 0) ? 1 : 0 );
 ..

 static void end_request(struct request *req, int uptodate) {
 struct bio *bio;
 while ((bio = req->bio) != NULL) {
             blk_finished_io(bio_sectors(bio));
             req->bio = bio->bi_next;
             bio->bi_next = NULL;
             bio_endio(bio, uptodate);
     }
     blk_put_request(req);
 }


It works fine except on error.  Kernel 2.5.31.  I understand that
put_request adds the request back to a free list (if gotten from there
via get_request).  The request is ordinary, except out of range ...
it's produced by an e2fsck of the device when the device itself is
unformatted, and the out of range request gets passed to the driver and
is errored there, and "kapow" ..

Peter

Re: end_request error procedure in 2.5?

[Jens Axboe]

On Mon, Sep 16 2002, Peter T. Breuer wrote:
> Can someone tell me why this block end_request routine works fine with a
> request that isn't errored, but locks the machine a milisecond or two
> later if the request is marked for erroring?
> 
> call as 
> 
>  end_request( req, (req->errors == 0) ? 1 : 0 );
>  ..
> 
>  static void end_request(struct request *req, int uptodate) {
>  struct bio *bio;
>  while ((bio = req->bio) != NULL) {
>              blk_finished_io(bio_sectors(bio));
>              req->bio = bio->bi_next;
>              bio->bi_next = NULL;
>              bio_endio(bio, uptodate);
>      }
>      blk_put_request(req);
>  }
> 
> 
> It works fine except on error.  Kernel 2.5.31.  I understand that
> put_request adds the request back to a free list (if gotten from there
> via get_request).  The request is ordinary, except out of range ...
> it's produced by an e2fsck of the device when the device itself is
> unformatted, and the out of range request gets passed to the driver and
> is errored there, and "kapow" ..

The error is most likely in the driver calling end_that_request_first(),
not the function itself. Maybe you can try to do at least some
debugging, I hope you are not expecting anyone to be able to help you
from the above report.

-- 
Jens Axboe

Re: end_request error procedure in 2.5?

[Peter T. Breuer]

"A month of sundays ago Jens Axboe wrote:"
> >  end_request( req, (req->errors == 0) ? 1 : 0 );
> >  ..
> > 
> >  static void end_request(struct request *req, int uptodate) {
> >  struct bio *bio;
> >  while ((bio = req->bio) != NULL) {
> >              blk_finished_io(bio_sectors(bio));
> >              req->bio = bio->bi_next;
> >              bio->bi_next = NULL;
> >              bio_endio(bio, uptodate);
> >      }
> >      blk_put_request(req);
> >  }
> > 
> > 
> > It works fine except on error.  Kernel 2.5.31.  I understand that
> > put_request adds the request back to a free list (if gotten from there
> > via get_request).  The request is ordinary, except out of range ...
> > it's produced by an e2fsck of the device when the device itself is
> > unformatted, and the out of range request gets passed to the driver and
> > is errored there, and "kapow" ..
> 
> The error is most likely in the driver calling end_that_request_first(),

Hmmm ... it's not called. The above is exactly all that is called
and LOCAL_END_REQUEST is set. OK. I see what you are saying. Yes, I
will direct my attention to that function instead ...

 ... and yes, I see a possible path in which the queue spinlock may be
taken twice. OK!

Thanks!

> not the function itself. Maybe you can try to do at least some
> debugging, I hope you are not expecting anyone to be able to help you
> from the above report.

!! :-)

Thanks, yes I know! However, it's taken me about 4 days to get it this
far. As you know, complete lockups are hard to debug! There's a race
condition between the printk appearing on the console and the machine
stopping :-(. 

Thanks again.

Peter

Re: end_request error procedure in 2.5?

[Jens Axboe]

On Mon, Sep 16 2002, Peter T. Breuer wrote:
> "A month of sundays ago Jens Axboe wrote:"
> > >  end_request( req, (req->errors == 0) ? 1 : 0 );
> > >  ..
> > > 
> > >  static void end_request(struct request *req, int uptodate) {
> > >  struct bio *bio;
> > >  while ((bio = req->bio) != NULL) {
> > >              blk_finished_io(bio_sectors(bio));
> > >              req->bio = bio->bi_next;
> > >              bio->bi_next = NULL;
> > >              bio_endio(bio, uptodate);
> > >      }
> > >      blk_put_request(req);
> > >  }
> > > 
> > > 
> > > It works fine except on error.  Kernel 2.5.31.  I understand that
> > > put_request adds the request back to a free list (if gotten from there
> > > via get_request).  The request is ordinary, except out of range ...
> > > it's produced by an e2fsck of the device when the device itself is
> > > unformatted, and the out of range request gets passed to the driver and
> > > is errored there, and "kapow" ..
> > 
> > The error is most likely in the driver calling end_that_request_first(),
> 
> Hmmm ... it's not called. The above is exactly all that is called
> and LOCAL_END_REQUEST is set. OK. I see what you are saying. Yes, I
> will direct my attention to that function instead ...
> 
>  ... and yes, I see a possible path in which the queue spinlock may be
> taken twice. OK!
> 
> Thanks!
> 
> > not the function itself. Maybe you can try to do at least some
> > debugging, I hope you are not expecting anyone to be able to help you
> > from the above report.
> 
> !! :-)
> 
> Thanks, yes I know! However, it's taken me about 4 days to get it this
> far. As you know, complete lockups are hard to debug! There's a race
> condition between the printk appearing on the console and the machine
> stopping :-(. 

NMI watchdog is invaluable for this sort of thing, beats printk by a
wide margin :-). Of course that only works of you have the hardware it
works on, but that's what test machines are for.

-- 
Jens Axboe