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    SubjectRe: 2.5 Problem Status Report
    On Wed, Sep 11 2002, Oleg Drokin wrote:
    > Hello!
    >
    > On Wed, Sep 11, 2002 at 12:29:26PM +0200, Jens Axboe wrote:
    >
    > > > ok I see the bug. it's due to the imbalanced nature of ide_map_buffer()
    > > > vs ide_unmap_buffer(). i'll cook up a fix right away.
    > > Does this make it work?
    >
    > No. It fails exactly like without the patch.

    Hmm, ok I'll try and reproduce it here then.

    > > --- include/linux/ide.h~ 2002-09-11 12:27:14.000000000 +0200
    > > +++ include/linux/ide.h 2002-09-11 12:27:29.000000000 +0200
    > > @@ -597,9 +597,10 @@
    > > return rq->buffer + task_rq_offset(rq);
    > > }
    > >
    > > -extern inline void ide_unmap_buffer(char *buffer, unsigned long *flags)
    > > +extern inline void ide_unmap_buffer(struct request *rq, char *buffer, unsigned long *flags)
    > > {
    > > - bio_kunmap_irq(buffer, flags);
    > > + if (rq->bio)
    > > + bio_kunmap_irq(buffer, flags);
    > > }
    > >
    > > /*
    >
    > Perhaps you forgot to make sure rq->bio is zeroed on unmapping/freeing?

    rq->bio must not be zeroed or free'd or anything like that. ok I see
    what happens now. does this patch work for you? just back out the other
    patch first (well you don't have to, but might as well).

    # This is a BitKeeper generated patch for the following project:
    # Project Name: Linux kernel tree
    # This patch format is intended for GNU patch command version 2.5 or higher.
    # This patch includes the following deltas:
    # ChangeSet 1.639 -> 1.640
    # include/linux/bio.h 1.17 -> 1.18
    #
    # The following is the BitKeeper ChangeSet Log
    # --------------------------------------------
    # 02/09/11 axboe@burns.home.kernel.dk 1.640
    # clean up with bio_kmap_irq() thing properly. remove the micro optimization
    # of _not_ calling kmap_atomic() if this isn't a highmem page. we could
    # keep that and do the inc_preempt_count() ourselves, but I'm not sure
    # it's worth it and this is cleaner.
    # --------------------------------------------
    #
    diff -Nru a/include/linux/bio.h b/include/linux/bio.h
    --- a/include/linux/bio.h Wed Sep 11 12:57:45 2002
    +++ b/include/linux/bio.h Wed Sep 11 12:57:45 2002
    @@ -215,17 +215,11 @@
    {
    unsigned long addr;

    - local_save_flags(*flags);
    -
    - /*
    - * could be low
    - */
    - if (!PageHighMem(bio_page(bio)))
    - return bio_data(bio);
    -
    /*
    - * it's a highmem page
    + * might not be a highmem page, but the preempt/irq count
    + * balancing is a lot nicer this way
    */
    + local_save_flags(*flags);
    local_irq_disable();
    addr = (unsigned long) kmap_atomic(bio_page(bio), KM_BIO_SRC_IRQ);

    --
    Jens Axboe

    -
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