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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