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    SubjectRe: [PATCH] [RFC] ataflop: remove buggy IRQ disable from do_fd_request()
    On Fri, 9 Oct 2009, Jens Axboe wrote:

    > On Fri, Oct 09 2009, Jiri Kosina 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
    > > 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.
    >
    > That does look odd. The comment is correct that the function is entered
    > with interrupts disabled (and the queue lock held). So I'd say your
    > patch looks fine, the whole save/restore business looks meaningless.
    >
    > Acked-by: Jens Axboe <jens.axboe@oracle.com>

    Thanks for confirming. I have queued it up in trivial tree.

    --
    Jiri Kosina
    SUSE Labs, Novell Inc.


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