Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writerlock backend
From: Srivatsa S. Bhat
Date: Mon Feb 11 2013 - 07:58:22 EST
On 02/11/2013 06:11 PM, David Howells wrote:
> Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote:
>> We can use global rwlocks as shown below safely, without fear of deadlocks:
>> 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:
> and on CPU 1 if CPU2 can do:
> 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.
Srivatsa S. Bhat
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