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

On Thu, 24 Mar 2022, Bjoern A. Zeeb wrote:

Hi,

> 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?


I just got bitten by this again running some older scripts missing
output.
Thankfully remembered the adjustment.

Is there any way we can solve this proper?

/bz



>>> 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