linux-kernel - Re: [PATCH v2 2/2] dyndbg: use the module notifier callbacks

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Message-ID: <c0c38c08-a329-9d0a-ca75-0519b589731e@akamai.com>
Date:   Tue, 28 Feb 2023 16:56:59 -0500
From:   Jason Baron <jbaron@...mai.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     jim.cromie@...il.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 2/2] dyndbg: use the module notifier callbacks



On 2/28/23 3:44 PM, Luis Chamberlain wrote:
> On Tue, Feb 28, 2023 at 02:35:02PM -0500, Jason Baron wrote:
>> As part of Jim Cromie's new dynamic debug classmap feature, the new code
>> tries to toggle a jump label from dynamic_debug_setup(). However,
>> dynamic_debug_setup() is called before the 'module_notify_list' notifier
>> chain is invoked. And jump labels are initialized via the module notifier
>> chain. Note this is an issue for a new feature not yet merged and doesn't
>> affect any existing codepaths.
> 
> I think we can summarize this to "in preperation for some future work where
> ordering matters with respect to jump labels" or something like that.
> 
> Because that is then making it specific to the future use case and
> creates the current justification.
> 
>> We could just move dynamic_debug_setup() earlier in load_module(). But
>> let's instead ensure the ordering via the 'priority' in the module list
>> notifier.
> 
> "becuase the notifier for jump labels jump_label_module_nb uses a
> priority of 1" or something like that would be nice to get added.
> 
>> This brings dynamic debug more in line with other subsystems and
>> pulls code out of the core module code.
> 
> This should be the main reason for this change, as explained in the
> commit log. A secondary benefit would be it fixes the first future bug
> mentioned.
> 
> With those changes I can take this into modules-next to start getting
> this tested sooner rather than later.
> 
>    Luis


Hi Luis,

Ok, I can fix up the commit message and re-post. I'm thinking maybe we 
should separate these patches as they are independent. The 2nd one I 
think makes sense to go through modules-next, but the first one is 
internal to dynamic debug and can be a part of Jim's series. Make sense?

Thanks,

-Jason