[dm-devel] [for-4.16 PATCH v3 2/3] block: allow gendisk's request_queue registration to be deferred

[Bart Van Assche]

On Thu, 2018-01-11 at 12:29 -0500, Mike Snitzer wrote:
> On Thu, Jan 11 2018 at 12:18pm -0500,
> Bart Van Assche <Bart.VanAssche at wdc.com> wrote:
> 
> > On Thu, 2018-01-11 at 12:04 -0500, Mike Snitzer wrote:
> > > So my v4, that I'll send out shortly, won't be using test_and_clear_bit()
> > 
> > Please use queue_flag_set(), queue_flag_clear(), queue_flag_test_and_clear() and/or
> > queue_flag_test_and_set() to manipulate queue flags.
> 
> Can you please expand on this?  My patch is only using test_bit().

Hello Mike,

I was referring to the following code, which apparenly is existing code:

        mutex_lock(&q->sysfs_lock);
        queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
        mutex_unlock(&q->sysfs_lock);

The above code is wrong. Other code that changes the queue flags protects
these changes with the the queue lock. The above code should be changed into
the following:

	spin_lock_irq(q->queue_lock);
	queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
	spin_unlock_irq(q->queue_lock);

The only functions from which it is safe to call queue_flag_(set|clear)_unlocked()
without holding the queue lock are blk_alloc_queue_node() and
__blk_release_queue() because for these functions it is guaranteed that no queue
flag changes can happen from another context, e.g. through a blk_set_queue_dying()
call.

Bart.