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Date: Thu, 25 May 2017 08:15:55 +0200 From: Ingo Molnar <mingo@...nel.org> To: Masami Hiramatsu <mhiramat@...nel.org> Cc: "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>, Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com> Subject: Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for optprobe wit CONFIG_PREEMPT * Masami Hiramatsu <mhiramat@...nel.org> wrote: > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -377,6 +377,23 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p) > static bool kprobes_allow_optimization; > > /* > + * Synchronizing wait on trampline code for interrupted tasks/threads. > + * Since the threads running on dynamically allocated trampline code > + * can be interrupted, kprobes has to wait for those tasks back on > + * track and scheduled. If the kernel is preemptive, the thread can be > + * preempted by other tasks on the trampoline too. For such case, this > + * calls synchronize_rcu_tasks() to wait for those tasks back on track. > + */ > +static void synchronize_on_trampoline(void) > +{ > +#ifdef CONFIG_PREEMPT > + synchronize_rcu_tasks(); > +#else > + synchronize_sched(); > +#endif > +} So that's really unacceptably ugly. Paul, I still question the need to have tasks-RCU as a Kconfig distinction, _especially_ if its API usage results in such ugly secondary #ifdefs... Why isn't there a single synchronize_rcu_tasks() API function, which does what is expected, where the _RCU_ code figures out how to implement it? I.e.: - There should be no user configurable TASKS_RCU Kconfig setting - at most a helper Kconfig that is automatically selected by the RCU code itself. - Both ftrace andkprobes would use a simple synchronize_rcu_tasks() call. Thanks, Ingo
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