Re: [PATCH 3/3] static_call: Fix static_call_update() sanity check

From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, jbaron@akamai.com, rostedt@goodmis.org,
	ardb@kernel.org, linux-kernel@vger.kernel.org,
	sumit.garg@linaro.org, oliver.sang@intel.com, jarkko@kernel.org,
	jeyu@kernel.org
Subject: Re: [PATCH 3/3] static_call: Fix static_call_update() sanity check
Date: Fri, 19 Mar 2021 13:57:38 +0100	[thread overview]
Message-ID: <YFSfwimq/VLmo1Lw@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YFOGvmWiJUDOHy7D@hirez.programming.kicks-ass.net>

On Thu, Mar 18, 2021 at 05:58:38PM +0100, Peter Zijlstra wrote:

> > For CONFIG_MODULE_UNLOAD, the code ends up in the normal text area, so
> > static_call_is_init() is false and kernel_text_address() is true.
> > 
> > For !CONFIG_MODULE_UNLOAD, the code gets discarded during module load,
> > so static_call_is_init() and kernel_text_address() are both false.  I
> > guess that will trigger a warning?
> 
> Oh gawd, more variants.
> 
> Afaict MODULE_UNLOAD, by virtue of that #ifdef in

!MODULE_UNLOAD (obv)

> rewrite_section_headers() won't even load the .exit sections. Afaict
> that will break: alterative, jump_label and static_call patching all in
> one go.

Jessica, can you explain how !MODULE_UNLOAD is supposed to work?
Alternatives, jump_labels and static_call all can have relocations into
__exit code. Not loading it at all would be BAD.

For alternatives all we really need it to discard it after init, for
jump_label and static_call we additinoally need to the code to identify
as init (ie, within_module_init() must return true for it).