Re: DTrace, kernel loader, unknown probes, enable on load?

On Mon, 14 Feb 2022, Mark Johnston wrote:

Hi,

sorry I had lost track ..

> On Sat, Feb 12, 2022 at 12:16:45AM +0000, Bjoern A. Zeeb wrote:
>> On Fri, 11 Feb 2022, Mark Johnston wrote:
>>
>>> It appears to be sufficient to simply move the kld_load hook to before
>>> module registration, patch below.  In the case of a subsequent error,
>>> the unload hook is called so DTrace gets a chance to clean up.  I can't
>>> see any reasons not to move it, though there's at least one non-dtrace
>>> consumer that needs a look.
>>
>> HWPMC?
>
> Yes.
>
>>
>> It does work for my case with -Z which will ease work massively.
>> I can't wait for the "morning" and more time then to look at things :-)
>>
>> Please put me on subscribers should you put up a review.
>
> So there's one wrinkle I haven't thought through: when FBT probes are
> enabled in a KLD, we use the kld_unload_try eventhandler to block
> unloading of the module.  Now, if we permit FBT probes to be enabled in
> a KLD before its sysinits run, then the kldload might fail, and the
> kernel linker will try to unload the module.  But then FBT will block
> the unload.  What's the right thing to do there?

I dunno.

I can only say that the local change has helped quite a few times in the
last month in my dev tree.

Shall we add a PR or review and track progress there with a possibly
wider audience?


>> Thanks a lot Mark and a happy weekend!
>> Bjoern
>>
>>
>>> diff --git a/sys/kern/kern_linker.c b/sys/kern/kern_linker.c
>>> index 2e4c95f16c8f..55661b9f9aa2 100644
>>> --- a/sys/kern/kern_linker.c
>>> +++ b/sys/kern/kern_linker.c
>>> @@ -452,6 +452,7 @@ linker_load_file(const char *filename, linker_file_t *result)
>>> 		if (error != ENOENT)
>>> 			foundfile = 1;
>>> 		if (lf) {
>>> +			EVENTHANDLER_INVOKE(kld_load, lf);
>>> 			error = linker_file_register_modules(lf);
>>> 			if (error == EEXIST) {
>>> 				linker_file_unload(lf, LINKER_UNLOAD_FORCE);
>>> @@ -472,7 +473,6 @@ linker_load_file(const char *filename, linker_file_t *result)
>>> 				return (ENOEXEC);
>>> 			}
>>> 			linker_file_enable_sysctls(lf);
>>> -			EVENTHANDLER_INVOKE(kld_load, lf);
>>> 			*result = lf;
>>> 			return (0);
>>> 		}
>>>
>>>
>>
>> --
>> Bjoern A. Zeeb                                                     r15:7
>
>

-- 
Bjoern A. Zeeb                                                     r15:7