Re: [patch] block/IDE/interrupt lockup

[Andrew Morton]

Manfred Spraul wrote:
> 
> > -     spin_unlock_irq(&io_request_lock);
> > +     spin_unlock_irqrestore(&io_request_lock, flags);
> >       rq = kmem_cache_alloc(request_cachep, SLAB_KERNEL);
> 
> Great patch.
> kmem_cache_alloc with SLAB_KERNEL can sleep, i.e. you've just converted
> an obvious bug into a rare, difficult to find bug. What about trying to
> fix it?

Gimme a break, Manfred.  The patch fixes the new bug. Which was
hardly obvious.  The longstanding (as in years-old) bug was
pointed out to the maintainer.  

It may not even be a bug.  Certainly I don't think it's
worth my time to fiddle with it.  But you're at liberty to.

> I agree that this won't happen during boot, but what about a hotplug PCI
> ide controller?

The kernel calls request_irq() inside cli() in lots of places.
That's the same bug: "if you called cli(), how come you're
allowing kmalloc to clear it?".

In 2.4, this is a design wart.  In 2.5, it will go BUG() if
the page allocator performs I/O.

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