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Date:   Fri, 11 Jan 2019 16:55:35 -0500
From:   Steven Rostedt <>
To:     Josh Poimboeuf <>
Cc:     Nadav Amit <>,
        Linus Torvalds <>,
        Andy Lutomirski <>,
        Peter Zijlstra <>,
        the arch/x86 maintainers <>,
        Linux List Kernel Mailing <>,
        Ard Biesheuvel <>,
        Ingo Molnar <>,
        Thomas Gleixner <>,
        Masami Hiramatsu <>,
        Jason Baron <>, Jiri Kosina <>,
        David Laight <>,
        Borislav Petkov <>,
        Julia Cartwright <>, Jessica Yu <>,
        "H. Peter Anvin" <>,
        Rasmus Villemoes <>,
        Edward Cree <>,
        Daniel Bristot de Oliveira <>
Subject: Re: [PATCH v3 0/6] Static calls

On Fri, 11 Jan 2019 15:41:22 -0600
Josh Poimboeuf <> wrote:

> > I don’t see RCU-sched solves the problem if you don’t disable preemption. On
> > a fully preemptable kernel, you can get preempted between the push and the
> > call (jmp) or before the push. RCU-sched can then finish, and the preempted
> > task may later jump to a wrong patched-dest.  
> Argh, I misspoke about RCU-sched.  Words are hard.
> I meant synchronize_rcu_tasks(), which is a completely different animal.
> My understanding is that it waits until all runnable tasks (including
> preempted tasks) have gotten a chance to run.

Not quite, but does the same thing. It waits for all tasks to either
schedule voluntarily (not preempted), or be / go into idle, or be /go
into userspace. In any case, it makes sure code is off of trampolines.
I use this before freeing trampolines used by ftrace.

-- Steve

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