netdev - Re: [GENETLINK]: Question: global lock (genl

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Date:	Fri, 20 Jul 2007 16:00:31 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Richard MUSIL <richard.musil@...com>
CC:	netdev@...r.kernel.org
Subject: Re: [GENETLINK]: Question: global lock (genl_mutex) possible refinement?

[ Please quote and break your lines appropriately ]

Richard MUSIL wrote:
> Patrick McHardy wrote:
>>
>>The usual way to do this for auto-loading of modules that register
>>things that take a mutex that is already held during netlink queue
>>processing, like qdiscs, classifiers, .. is:
>>
>>- look for <qdisc/classifier/...>, if not found:
>>- drop mutex (using the __ unlock variant to avoid reentering queue
>>processing)
>>- perform module loading (which takes the mutex and registers itself)
>>- grab mutex again
>>- look for <qdisc/classifier/...> again
>>- if not found return -ENOENT
>>- if found drop reference, return -EAGAIN
>>
>>The caller is changed to handle -EAGAIN by replaying the entire
>>request. Your problem sounds very similar, look at net/sched/sch_api.c
>>for an example.
> 
> 
> The aforementioned mutex is local to genetlink module, so I cannot temporarily drop it, call the stuff and grab it again (which was mine original thought too).

Export the lock/unlock/.. functions. You'll also need a new version
similar to __rtnl_unlock.
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