Messages in this thread | | | From | "Adam J. Richter" <> | Date | Fri, 10 Jan 2003 04:18:58 -0800 | Subject | Re: Another idea for simplifying locking in kernel/module.c |
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Rusty Russell wrote: >In message <200301100910.BAA31409@adam.yggdrasil.com> you write: >> Rusty Russell wrote: >> >In message <200301070219.SAA12905@adam.yggdrasil.com> you write: >> >> Here is a way to replace all of the specialized "stop CPU" >> >> locking code in kernel/module.c with an rw_semaphore by using >> >> down_read_trylock in try_module_get() and down_write when beginning to >> >> unload the module. >> >> >And now you can't modularize netfilter modules. >> >> Why not? Last time you went looking in the networking code >> for an example of something that had to increment a module reference >> in a context where blocking was not allowed you ended up conceding >> that you example was incorrect.
>No, you're thinking of the IPv4 stack. I didn't use netfilter as an >example, because that opens me to "well, FIX NETFILTER then!". If it >were the only case, it's probably arguable.
>The problems with netfilter modules are exactly why I started looking >at module locking over two years ago.
>> I just booted my gateway machine to a kernel using my >> aforemetioned patch and various netfilter modules. I've surfed the >> web, FTP'ed file and run irc through it. It seems to be okay.
>Sure! That's because the netfilter modules use a horrific hack, by >keeping their own "usage" counts and then spinning (potentially >forever) on unload until it hits zero. [...]
Although I suspect that this could be fixed so that the spinning is guanteed not to be forever, it happens that my module_put(), which is the same as your module_put() is non-blocking (as is my try_module_get(), by the way). So I don't see what the problem is. You should still be able to call try_module_get and module_put from an interrupt context.
Adam J. Richter __ ______________ 575 Oroville Road adam@yggdrasil.com \ / Milpitas, California 95035 +1 408 309-6081 | g g d r a s i l United States of America "Free Software For The Rest Of Us."
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