Messages in this thread | | | Date | Thu, 7 Jul 2022 17:57:50 +0100 | From | Aaron Tomlin <> | Subject | Re: [PATCH v2] module: kallsyms: Ensure preemption in add_kallsyms() with PREEMPT_RT |
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On Wed 2022-07-06 10:58 -0700, Luis Chamberlain wrote: > Hey Aaron, thanks again!
Hi Luis,
No problem :)
> On Mon, Jul 04, 2022 at 05:17:53PM +0100, Aaron Tomlin wrote: > > To disable preemption in the context of add_kallsyms() is incorrect. > > Why, what broke? Did this used to work? Was the commit in question a > regression then? Clarifying all this will help a lot.
Sorry for the confusion! If I understand correctly, nothing broke intrinsically.
Rather with commit 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage") under PREEMPT_RT=y, by disabling preemption, I introduced an unbounded latency since the loop is not fixed which is generally frowned upon. So, I would say this was a regression since earlier preemption was not disabled and we would dereference RCU-protected pointers explicitly i.e. without using the more appropriate rcu_dereference() family of primitives. That being said, these pointers cannot change in this context as explained previously.
Would the above be suitable - just to confirm before I send another iteration?
Kind regards,
-- Aaron Tomlin
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