Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend

On 02/11/2013 06:11 PM, David Howells wrote:

Srivatsa S. Bhat [off-list ref] wrote:

quoted

We can use global rwlocks as shown below safely, without fear of deadlocks:

Readers:

         CPU 0                                CPU 1
         ------                               ------

1.    spin_lock(&random_lock);             read_lock(&my_rwlock);


2.    read_lock(&my_rwlock);               spin_lock(&random_lock);

The lock order on CPU 0 is unsafe if CPU2 can do:

	write_lock(&my_rwlock);
	spin_lock(&random_lock);

and on CPU 1 if CPU2 can do:

	spin_lock(&random_lock);
	write_lock(&my_rwlock);

Right..

I presume you were specifically excluding these situations?

Yes.. Those cases are simple to find out and fix (by changing the
lock ordering). My main problem was with CPU 0 and CPU 1 as shown above..
... and using a global rwlock helps ease that part out.

Regards,
Srivatsa S. Bhat