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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
	dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com,
	fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 11/15] rcu: Break more call_rcu() deadlock involving scheduler and perf
Date: Mon, 1 Sep 2014 13:29:34 +0200	[thread overview]
Message-ID: <20140901112934.GH27892@worktop.ger.corp.intel.com> (raw)
In-Reply-To: <1409250394-25159-11-git-send-email-paulmck@linux.vnet.ibm.com>

On Thu, Aug 28, 2014 at 11:26:30AM -0700, Paul E. McKenney wrote:

> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index b6acb9340192..a1af86099a67 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2121,16 +2121,23 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
>  			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
>  					    TPS("WakeEmpty"));
>  		} else {
> -			rdp->nocb_defer_wakeup = true;
> +			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
>  			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
>  					    TPS("WakeEmptyIsDeferred"));
>  		}
>  		rdp->qlen_last_fqs_check = 0;
>  	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
>  		/* ... or if many callbacks queued. */
> -		wake_nocb_leader(rdp, true);
> +		if (!irqs_disabled_flags(flags)) {
> +			wake_nocb_leader(rdp, true);
> +			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
> +					    TPS("WakeOvf"));
> +		} else {
> +			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
> +			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
> +					    TPS("WakeOvfIsDeferred"));
> +		}
>  		rdp->qlen_last_fqs_check = LONG_MAX / 2;
> -		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
>  	} else {
>  		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
>  	}

Is it possible for the RCU_NOCP_WAKE write to overwrite a WAKE_FORCE ?
If not, why not? (Would make a good comment thereabouts).

  reply	other threads:[~2014-09-01 11:29 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-28 18:26 [PATCH tip/core/rcu 0/15] Miscellaneous fixes for 3.18 Paul E. McKenney
2014-08-28 18:26 ` [PATCH tip/core/rcu 01/15] rcu: Remove remaining read-modify-write ACCESS_ONCE() calls Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 02/15] rcu: Fix sparse warning about rcu_batches_completed_preempt() being non-static Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 03/15] rcu: Use bool type for return value in rcu_is_watching() Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 04/15] rcu: Return bool type for rcu_try_advance_all_cbs() Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 05/15] rcu: Return bool type in rcu_lockdep_current_cpu_online() Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 06/15] rcu: Use true/false instead of 1/0 for a bool type Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 07/15] rcu: Uninline rcu_read_lock_held() Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 08/15] rcu: Define tracepoint strings only if CONFIG_TRACING is set Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 09/15] rcu: Update tiny.c references to tree.c Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 10/15] rcu: Remove stale comment in tree.c Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 11/15] rcu: Break more call_rcu() deadlock involving scheduler and perf Paul E. McKenney
2014-09-01 11:29     ` Peter Zijlstra [this message]
2014-09-01 16:20       ` Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 12/15] rcu: Make TINY_RCU tinier by putting error checks under #ifdef Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 13/15] rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 14/15] rcu: Replace flush_signals() with WARN_ON(signal_pending()) Paul E. McKenney
2014-08-28 18:26   ` [PATCH tip/core/rcu 15/15] rcu: Add ACCESS_ONCE() for RCU_INIT_POINTER() Paul E. McKenney

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