Date: Wed, 02 Aug 2017 10:49:51 -0600 From: Ian Lepore <ian@freebsd.org> To: John Baldwin <jhb@freebsd.org>, freebsd-current@freebsd.org Cc: Hans Petter Selasky <hps@selasky.org>, Andriy Gapon <avg@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: order of executing MOD_LOAD and registering module sysctl-s Message-ID: <1501692591.90400.142.camel@freebsd.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 Wed, 2017-08-02 at 08:49 -0700, 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. > > > > 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. > But if module sysctls are registered last then the ones flagged as CTLFLAG_TUN won't have their tunable values populated before the MOD_LOAD handler runs, is that going to cause trouble? It would suck to have to handle things differently in a driver depending on whether you're compiled into the kernel or kldload'd interactively. -- Ian
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