Re: Fwd: [PATCH] [RFC] ataflop: remove buggy IRQ disable from do_fd_request()

[Jens Axboe <jens.axboe@oracle.com>]

On Sun, Oct 11 2009, Michael Schmitz wrote:
> Hi Geert,
> 
> > 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.

What buggy comments? The comments states that interrupts are already
disabled when entering this function, which is correct. The point is
that doing a flags save and then an irq disable is pointless, since we
KNOW that interrupts are already disabled.

-- 
Jens Axboe