Messages in this thread | | | Date | Thu, 14 Nov 2019 16:28:29 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH -v5 12/17] x86/kprobes: Fix ordering |
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On Thu, Nov 14, 2019 at 10:22:24AM -0500, Mathieu Desnoyers wrote:
> >> > So what we do, after enabling the regular kprobe, is call > >> > synchronize_rcu_tasks() to wait for each task to have passed through > >> > schedule(). That guarantees no task is preempted inside the kprobe > >> > shadow (when it triggers it ensures it resumes execution at an > >> > instruction boundary further than 5 bytes away). > >> > >> Indeed, given that synchronize_rcu_tasks() awaits for voluntary context > >> switches (or user-space execution), it guarantees that no task was preempted > >> within the kprobe shadow. > >> > >> Considering that synchronize_rcu_tasks() is meant only for code rewriting, > >> I wonder if it would make sense to include the core serializing guarantees > >> within this RCU API ? > > > > As in have synchronize_rcu_tasks() do the IPI-sync love before doing > > the current wait-for-voluntary-context-switch work? > > This is what I have in mind, yes, based on the assumption that the only > intended use-case for synchronize_rcu_tasks() is code patching.
I don't think that is needed. As per the patch under discussion, we unconditionally need that IPI-sync (even for !optimized) but we only need the synchonize_rcu_tasks() thing for optimized kprobes.
Also, they really do two different things. Lets not tie them together.
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