Messages in this thread | | | From | Keith Owens <> | Subject | Re: Linux 2.4.21-rc3 - ipmi unresolved | Date | Tue, 27 May 2003 13:09:09 +1000 |
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On Mon, 26 May 2003 19:30:04 -0500, Corey Minyard <minyard@acm.org> wrote: >Keith Owens wrote: >>I considered making notifier_chain_register() a macro which called >>notifier_chain_register_module() with __THIS_MODULE, but that assumes >>that all calls to notifier_chain_register() are local, i.e. from the >>top level functions. Alas there are any service routines that call >>notifier_chain_register() on behalf of their caller, so the macro >>approach will result in the wrong value for __THIS_MODULE. >> >Why can't you have a module id in the notifier chain, and use a boolean >to tell if it is set, or something similar to that? That way you could >mix them, if the bool is set then do the try_in_module_count thing, if >not then just call the function. It does add some components to the >register structure, but that shouldn't hurt anything besides taking a >little more memory.
It is a change of API in a 2.4 kernel. Not a good idea.
>>notifier_chain_unregister() is not a problem, that is a downcall from >>the module into the kernel when the module is going away, downcalls are >>"always" safe. The race is a module that has started to unload, and >>another cpu (or even the same cpu under some circumstances) runs the >>notifier chain, doing an upcall from the kernel into a module without >>locking or refcounts. Given the right timing, the notifier code could >>even branch to a module that has been completely removed. Note that >>notifier_call_chain() has no locking, so it is also racy against >>notifier_chain_unregister(). >> >> >You don't understand how the RCU code works.
(a) I understand how RCU works, I was working on lock free code for years before RCU appeared in the kernel.
(b) This is 2.4, not 2.5, there is no RCU.
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