[ restoring original recepient list, and thus keeping all your text
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On Sun, 11 Oct 2009, Michael Schmitz wrote:
> > There is a nice gem in drivers/block/ataflop.c::do_fd_request()
> >
> > void do_fd_request(struct request_queue * q)
> > {
> > unsigned long flags;
> >
> > DPRINT(("do_fd_request for pid %d\n",current->pid));
> > while( fdc_busy ) sleep_on( &fdc_wait );
> > fdc_busy = 1;
> > stdma_lock(floppy_irq, NULL);
> >
> > atari_disable_irq( IRQ_MFP_FDC );
> > local_save_flags(flags); /* The request function is
> > called with ints
> > local_irq_disable(); * disabled... so must save the
> > IPL
> > for later */
> > redo_fd_request();
> > local_irq_restore(flags);
> > atari_enable_irq( IRQ_MFP_FDC );
> > }
> >
> > If you look at the code long enough, you will notioce that the
> > local_irq_disable() call is actually commented out. This has been
> > introduced back in 2002 in [1], but as you can see, the same bug has been
> > there even before, with the sti() call being commented out in the very
> > same way :)
> >
> > I am not familiar with the code myself at all, but I guess that the whole
> > stuff can just be removed. Why do we need save_flags/restore_flags at all,
> > without actually disabling the local IRQs afterwards? The
>
> The IRQ source has been disabled in the MFC by the atari_disable_irq(
> IRQ_MFP_FDC ) call just before local_save_flags(flags). For that reason,
> the fact that local_irq_disable is commented out will not usually matter
> (a timer interrupt that would result in retrying the floppy request or
> removing the request from the queue excepted).
>
> I would rather suggest to leave the code in, and fix the buggy comments
> instead.
>
> Note: IDE or SCSI cannot get in the way here -and I haven't seen IDE and
> floppy races in recent kernels. SCSI was pretty broken anyway last time I
> tried
> a few months ago. I cannot run any tests since my PC motherboard or CPU died
> recently.
>
> > redo_fd_request() doesn't seem to do anything that would mess with flags
> > inconsistently.
> >
> > But I'd rather anyone who has touched the surrounding code in past years
> > Ack it. I can then take it through trivial tree or submit to akpm.
>
> The surounding code probably hasn't been touched in ages. The floppy driver
> in
> its current state does work. If redo_fd_request could alter timers ot queues,
> rmoving the locking would be dangerous, no?
The patch is not removing any locking. It only
1) removes the local_irq_disable() that has been commented out for many
years already anyway
2) removes the saving and restoring of CPU flags around do_fd_request(),
which is rather clearly a nop than any kind of "locking"
> > [1] http://lkml.org/lkml/2002/12/27/58
> >
> > Signed-off-by: Jiri Kosina <[email protected]>
>
> NAck for my part.
Please elaborate a little bit more which of the two points above you base
your NACK on.
>
> Michael
>
>
> > ---
> > drivers/block/ataflop.c | 3 ---
> > 1 files changed, 0 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/block/ataflop.c b/drivers/block/ataflop.c
> > index 847a9e5..a5af1d6 100644
> > --- a/drivers/block/ataflop.c
> > +++ b/drivers/block/ataflop.c
> > @@ -1478,10 +1478,7 @@ void do_fd_request(struct request_queue * q)
> > stdma_lock(floppy_irq, NULL);
> >
> > atari_disable_irq( IRQ_MFP_FDC );
> > - local_save_flags(flags); /* The request function is called with
> > ints
> > - local_irq_disable(); * disabled... so must save the IPL for
> > later */
> > redo_fd_request();
> > - local_irq_restore(flags);
> > atari_enable_irq( IRQ_MFP_FDC );
> > }
> >
--
Jiri Kosina
SUSE Labs, Novell Inc.
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