Re: [bug, 2.6.26-rc4/rc5] sporadic bootup crashes inblk_lookup_devt()/prepare_namespace()

[Cornelia Huck]

On Mon, 9 Jun 2008 09:15:40 -0700 (PDT),
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> And this is all still ignoring the locking issue, of course. It would be 
> trivial to just remove the block_class_lock, and change
> 
> 	mutex_[un]lock(&block_class_lock);
> 
> into
> 
> 	down|up(&block_class.sem);
> 
> except for _one_ case, which is
> 
> 	bdev_map = kobj_map_init(base_probe, &block_class_lock);
> 
> which really wants a mutex, not a sempahore.
> 
> So to fix that, we'd need to make the class->sem be a mutex, and pass that 
> in. Which is probably a good change too, but makes the whole thing much 
> bigger.

The driver core changes in -next convert class->sem to
class->p->class_mutex, which makes it non-accessible to drivers.
Most of the locking is easily done through converting to the class
iterator functions, but there are some cases where this is not going to
work:

- The {register,unregister}_blkdev() functions, which don't directly
involve the class.
- The iterators for /proc/partitions, which take the lock in
part_start() and give it up again in part_stop().

Maybe we need a possibilty for a driver to lock a class from outside?
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