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Re: locking order between softnet_lock and the kernel lock

Greg Troxel <> writes:

> Thor Lancelot Simon <> writes:
>> On Mon, Mar 26, 2012 at 02:38:44PM -0400, Beverly Schwartz wrote:
>>> Here at BBN, we are getting a hang with heavy use of networking code
>>> and looking for possible deadlocks.  We've made modifications to the
>>> kernel.  I'm trying to understand the lock order invariants to make
>>> sure we have applied it correctly to our code.
>> Generally speaking, I don't think we require locks to be released
>> in order - though of course it is good practice.
> I'd agree with that, but I think Bev is concerned about two locks A and
> B where the taking order is A then B and
> take A
> take B
> release A
> *
> take A
> and if someone else grabs A at *, then the other is waiting for B and we
> are waiting for B.   So out of order releasing seems fine, but once
> starting to release I think you have to release all the way.
> But I am feeling a bit fuzzy on this.

so self-replying in light of yamt@'s answer, I remember now that the
kernel lock is special in that processes that try to take a mutex while
holding the kernel lock will give up the kernel lock while sleeping and
then reacquire it on waking.

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