Messages in this thread | | | Date | Thu, 14 Nov 2019 10:30:01 -0500 (EST) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH -v5 12/17] x86/kprobes: Fix ordering |
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----- On Nov 14, 2019, at 10:28 AM, Peter Zijlstra peterz@infradead.org wrote:
> 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.
I'm fine with this approach, I just thought it would be good to consider the alternative.
Thanks!
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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