Date: Wed, 02 Aug 2017 08:49:46 -0700 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Hans Petter Selasky <hps@selasky.org>, Andriy Gapon <avg@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: order of executing MOD_LOAD and registering module sysctl-s Message-ID: <2718016.8bPh6cqhGc@ralph.baldwin.cx> In-Reply-To: <c73441ae-e623-3828-d10e-74947c78240b@selasky.org> References: <62e7ab4d-8956-545e-b204-4fb63cfe5fbf@FreeBSD.org> <c73441ae-e623-3828-d10e-74947c78240b@selasky.org>
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On Wednesday, August 02, 2017 12:39:36 PM Hans Petter Selasky wrote: > On 08/02/17 12:13, Andriy Gapon wrote: > > > > As far as I understand a module initialization routine is executed via the > > sysinit mechanism. Specifically, module_register_init is set up as the sysinit > > function for every module and it calls MOD_EVENT(mod, MOD_LOAD) to invoke the > > module event handler. > > > > In linker_load_file() I see the following code: > > linker_file_register_sysctls(lf); > > linker_file_sysinit(lf); > > > > I think that this means that any statically declared sysctl-s in the module > > would be registered before the module receives the MOD_LOAD event. > > It's possible that some of the sysctl-s could have procedures as handlers and > > they might access data that is supposed to be initialized by the module event > > handler. > > > > So, for example, running sysctl -a at just the right moment during the loading > > of a module might end up in an expected behavior (including a crash). > > > > Is my interpretation of how the code works correct? > > Can the order of linker_file_sysinit and linker_file_register_sysctls be changed > > without a great risk? > > > > Thank you! > > > > P.S. > > The same applies to: > > linker_file_sysuninit(file); > > linker_file_unregister_sysctls(file); > > > > Hi, > > Not sure if this answers your question. > > If a SYSCTL() is TUNABLE, it's procedure can be called when the sysctl > is created. Else the SYSCTL() procedure callback might be called right > after it's registered. I think there is an own subsystem in sys/kernel.h > which takes care of the actual SYSCTL() creation/destruction - after the > linker is involved. sysctl nodes are created explicitly via linker_file_register_sysctls, not via SYSINITs, so you can't order them with respect to other init functions. I think Andriy's suggestion of doing sysctls "inside" sysinits (so they are registered last and unregistered first) is probably better than the current state and is a simpler fix than changing all sysctls to use SYSINITs. -- John Baldwin
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