From: Patrick McHardy <kaber@trash•net>
To: Richard MUSIL <richard.musil@st•com>
Cc: netdev@vger•kernel.org
Subject: Re: [GENETLINK]: Question: global lock (genl_mutex) possible refinement?
Date: Fri, 20 Jul 2007 15:21:34 +0200 [thread overview]
Message-ID: <46A0B6DE.1080904@trash.net> (raw)
In-Reply-To: <46A0B017.4080505@st.com>
Richard MUSIL wrote:
> I am currently trying to write a module which communicates with user space using NETLINK_GENERIC. This module (dev_mgr) manages virtual devices which are also supposed to use genetlink for communication with user space.
>
> I want to do something like that:
> dev_mgr <- receives message from user space to create new device
> dev_mgr inside 'doit' handler:
> 1. creates device
> 2. registers new genetlink family for the device
> 3. returns family name and id to user
>
> This should work similarly for device removal.
>
> After few reboots I found out that 2. blocks on genl_mutex, since this mutex is already acquired when genl_register_family is called (by genl_rcv).
>
> I do not see why registering new family (when processing message for another family) should be a problem. In fact from genl_lock and genl_trylock occurrence it seems that genl_mutex is mostly used for syncing access to family list and also for message processing.
> Since I am not (yet) familiar enough with (ge)netlink internals I am asking:
> Would it make sense to split the mutex into two, one for family list and one for messaging, so it would be possible to change families when processing the message?
>
> Simple split could introduce possible danger of user removing family inside processing of the message for this particular family, but would this really be a danger?
>
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.
next prev parent reply other threads:[~2007-07-20 13:25 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-20 12:52 [GENETLINK]: Question: global lock (genl_mutex) possible refinement? Richard MUSIL
2007-07-20 13:21 ` Patrick McHardy [this message]
2007-07-20 13:58 ` Richard MUSIL
2007-07-20 14:00 ` Patrick McHardy
2007-07-20 16:15 ` Richard MUSIL
2007-07-23 10:29 ` Thomas Graf
2007-07-23 16:45 ` Richard MUSIL
2007-07-24 9:35 ` Thomas Graf
2007-07-24 11:09 ` Richard MUSIL
2007-08-10 8:52 ` Richard MUSIL
2007-08-16 15:58 ` Thomas Graf
2007-08-17 8:38 ` Richard MUSIL
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