corruption with mtdblock

[Nicolas Pitre]

On Mon, 6 Nov 2000, David Woodhouse wrote:

> 
> nico at cam.org said:
> >  So in our case, q->head_active is 1 by default.
> > Looking at __make_request() you can see the head of the queue is
> > actually skipped when the queue is unplugged.  It is plugged only when
> > actually empty and no request are processed until it gets unplugged
> > again.  All this is done when io_request_lock is held.  That's why I
> > came to the conclusion that requests don't have to be removed earlier.
> > 
> 
> OK. How about 'plugging'?
> 
> The code looks like this...
> 
>         /*
>          * skip first entry, for devices with active queue head
>          */
>         if (q->head_active && !q->plugged)
>                 head = head->next;
> 
> 
> It may be that if our request function returns without first ending the 
> request (as it does, because all it does is a wake_up()), the queue is 
> 'plugged' to wait for requests to be merged. 

Nope.  The only place where the queue can be plugged is:

        if (list_empty(head)) {
                q->plug_device_fn(q, bh->b_rdev); /* is atomic */

Therefore the queue can't be plugged until we emptied it.

To be sure I tried to disable plugging by providing a dummy plug function
that does nothing.  No difference.


Nicolas



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