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Date: Fri, 8 Aug 2014 09:39:05 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Steven Rostedt <rostedt@...dmis.org>, Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org, mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, bobby.prani@...il.com, masami.hiramatsu.pt@...achi.com Subject: Re: [PATCH v3 tip/core/rcu 3/9] rcu: Add synchronous grace-period waiting for RCU-tasks On Fri, Aug 08, 2014 at 06:27:14PM +0200, Peter Zijlstra wrote: > On Fri, Aug 08, 2014 at 10:58:58AM -0400, Steven Rostedt wrote: > > > > > No, they are also used by optimized kprobes. This is why optimized > > > > kprobes depend on !CONFIG_PREEMPT. [ added Masami to the discussion ]. > > > > > > How do those work? Is that one where the INT3 relocates the instruction > > > stream into an alternative 'text' and that JMPs back into the original > > > stream at the end? > > > > No, it's where we replace the 'int3' with a jump to a trampoline that > > simulates an INT3. Speeds things up quite a bit. > > OK, so the trivial 'fix' for that is to patch the probe site like: > > preempt_disable(); INC GS:%__preempt_count > call trampoline; CALL 0xDEADBEEF > preempt_enable(); DEC GS:%__preempt_count > JNZ 1f > CALL ___preempt_schedule > 1f: > > At which point the preempt_disable/enable() are the read side primitives > and call_rcu_sched/synchronize_sched are sufficient to release it. Unless this is done in idle, at which point RCU-sched is studiously ignoring any preempt_disable() sections. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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