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Date: Mon, 02 Jul 2012 13:59:12 +0200 From: Peter Zijlstra <peterz@...radead.org> To: paulmck@...ux.vnet.ibm.com Cc: Sasha Levin <levinsasha928@...il.com>, Dave Jones <davej@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: rcu: BUG: spinlock recursion on CPU#3, trinity-child19/5970 On Mon, 2012-07-02 at 04:35 -0700, Paul E. McKenney wrote: > On Mon, Jul 02, 2012 at 12:32:19PM +0200, Peter Zijlstra wrote: > > On Fri, 2012-06-29 at 23:40 +0200, Sasha Levin wrote: > > > > > > The bad news are that what you saw was a lockdep enabled run > > > (CONFIG_PROVE_RCU is enabled, and lockdep was enabled). There were no > > > lockdep warnings at any point while reproducing it. > > > > rcu_switch_from() -> rcu_preempt_note_context_switch() is called _after_ > > the lockdep context switch annotation. Therefore lockdep things the prev > > task isn't holding any locks anymore. > > In other words, moving rcu_preempt_note_context_switch() deeper into > the scheduler is totally bogus, and I need to move it back out into the > original rcu_note_context_switch(), reverting 616c310e (Move PREEMPT_RCU > preemption to switch_to() invocation), correct? > > Sigh. "It seemed like a good idea at the time." It only needs moving back before that spin_release() thing. But unless there's a reason to do it later, something like the below might be the right thing. --- kernel/sched/core.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9bb7d28..7e20e6c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1914,6 +1914,7 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev, sched_info_switch(prev, next); perf_event_task_sched_out(prev, next); fire_sched_out_preempt_notifiers(prev, next); + rcu_switch_from(prev); prepare_lock_switch(rq, next); prepare_arch_switch(next); trace_sched_switch(prev, next); @@ -2082,7 +2083,6 @@ context_switch(struct rq *rq, struct task_struct *prev, #endif /* Here we just switch the register state and the stack. */ - rcu_switch_from(prev); switch_to(prev, next, prev); barrier(); -- 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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