Messages in this thread | | | Date | Thu, 06 Sep 2007 12:33:52 +0200 | From | Patrick McHardy <> | Subject | Re: [PATCH 0/2] Fix (improve) deadlock condition on module removal netfilter socket option removal |
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Neil Horman wrote: > On Thu, Sep 06, 2007 at 02:13:26AM +1000, Rusty Russell wrote: > >>On Wed, 2007-09-05 at 17:22 +0200, Patrick McHardy wrote: >> >>>But I'm wondering, wouldn't module refcounting alone fix this problem? >>>If we make nf_sockopt() call try_module_get(ops->owner), remove_module() >>>on ip_tables.ko would simply fail because the refcount is above zero >>>(so it would fail at point 3 above). Am I missing something important? >> >>Yes, that seems the correct solution to me, too. ISTR that this code >>predates the current module code. >> >>Rusty. > > > Thanks guys- > When I first started looking at this problem I would have agreed with > you, that module reference counting alone would fix the problem. However, > delete_module can work in either a non-blocking or a blocking mode. rmmod > passes O_NONBLOCK to delete module, and so is fine, but modprobe does not. So > if you currently use modprobe -r to remove modules (as the iptables service > script nominally does), modprobe winds up waiting in the kernel for the module > reference count to become zero. Since we can hold a reference to the module > being removed in the same path that forks a modprobe request to load that same > module (which then blocks on the first modprobes fcntl lock), we still get > deadlock. The way I fixed this was by use of the second patch, which brings > modprobes behavior into line with the rmmod utility (which is to default to > non-blocking operation), leading to the remove_module failure and breaking of > the deadlock that you describe above.
Thanks for the explanation, I've applied your patch. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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