Date: Wed, 2 Aug 2017 18:53:54 +0200 From: Hans Petter Selasky <hps@selasky.org> To: John Baldwin <jhb@freebsd.org>, freebsd-current@freebsd.org Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, Andriy Gapon <avg@freebsd.org> Subject: Re: order of executing MOD_LOAD and registering module sysctl-s Message-ID: <1c40d6ef-bfd2-d8ee-e057-47cd8d695544@selasky.org> In-Reply-To: <2718016.8bPh6cqhGc@ralph.baldwin.cx> References: <62e7ab4d-8956-545e-b204-4fb63cfe5fbf@FreeBSD.org> <c73441ae-e623-3828-d10e-74947c78240b@selasky.org> <2718016.8bPh6cqhGc@ralph.baldwin.cx>
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On 08/02/17 17:49, John Baldwin wrote: > 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. >> Hi, >> 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. For GENERIC (non-modules) the SYSCTLS() are registered by sysctl_register_all() at SYSINIT(sysctl, SI_SUB_KMEM, SI_ORDER_FIRST, sysctl_register_all, 0); > > 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. > If the module provided SYSCTLS's could use the same SI_SUB_KMEM it would be compatible. You have three cases to think about: 1) SYSCTLS's in modules loaded before the kernel is booted 2) SYSCTLS's in modules after the kernel is booted 3) SYSCTLS's in the GENERIC kernel. I'm not 100% sure, but I think 1) and 2) are treated differently. Correct me if I'm wrong. --HPS
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