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From: Peter Zijlstra <peterz@infradead.org>
To: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, joe.lawrence@redhat.com,
	fweisbec@gmail.com, tglx@linutronix.de, hca@linux.ibm.com,
	svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, x86@kernel.org
Subject: Re: [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking
Date: Wed, 29 Sep 2021 20:54:35 +0200	[thread overview]
Message-ID: <20210929185435.GW4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20210929152429.007420590@infradead.org>

On Wed, Sep 29, 2021 at 05:17:31PM +0200, Peter Zijlstra wrote:
> XXX I'm pretty sure I broke task-trace-rcu.

> -static noinstr void rcu_dynticks_eqs_enter(void)
> -{
> -	int seq;
> -
> -	/*
> -	 * CPUs seeing atomic_add_return() must see prior RCU read-side
> -	 * critical sections, and we also must force ordering with the
> -	 * next idle sojourn.
> -	 */
> -	rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
> -	seq = rcu_dynticks_inc(1);
> -	// RCU is no longer watching.  Better be in extended quiescent state!
> -	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & 0x1));
> -}

> -static noinstr void rcu_dynticks_eqs_exit(void)
> -{
> -	int seq;
> -
> -	/*
> -	 * CPUs seeing atomic_add_return() must see prior idle sojourns,
> -	 * and we also must force ordering with the next RCU read-side
> -	 * critical section.
> -	 */
> -	seq = rcu_dynticks_inc(1);
> -	// RCU is now watching.  Better not be in an extended quiescent state!
> -	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
> -	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & 0x1));
> -}

So specifically rcu_dynticks_task_trace_{enter,exit}() are now orphaned.
After this patch, nothing calls them.

However, looking at this again, we've got:

  __context_tracking_enter()
    rcu_user_enter()
      rcu_eqs_enter()
        rcu_dynticks_eqs_enter()
	  rcu_dynticks_task_trace_enter()
	  rcu_dynticks_inc();
	rcu_dynticks_task_enter();

    ct_seq_user_enter()
      atomic_add_return()

and on the other end:

  __context_tracking_exit()
    ct_seq_user_exit()
      atomic_add_return()

    rcu_user_exit()
      rcu_esq_exit()
        rcu_dynticks_task_exit()
	rcu_dynticks_eqs_exit()
	  rcu_dynticks_inc()
	  rcu_dynticks_task_trace_exit()

And since we want to replace dynticks_inc() with ct_seq_*() the
rcu_dynticks_task_{enter,exit}() ought to be pulled before that..

Instead I orphaned rcu_dynticks_task_trace_{enter,exit}() which should
more or less stay where they are.

I seems to have confused the two :/


  parent reply	other threads:[~2021-09-29 18:55 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40   ` Petr Mladek
2021-10-05 14:03     ` Peter Zijlstra
2021-10-06  8:59   ` Miroslav Benes
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-10-13 14:32   ` [PATCH v2 04/11] " Qian Cai
2021-10-19  3:47     ` Qian Cai
2021-10-19  8:56       ` Peter Zijlstra
2021-10-19  9:10         ` Peter Zijlstra
2021-10-19 15:32           ` Qian Cai
2021-10-19 15:50             ` Peter Zijlstra
2021-10-19 19:22               ` Qian Cai
2021-10-19 20:27                 ` Peter Zijlstra
     [not found]   ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46     ` Marek Szyprowski
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00   ` Petr Mladek
2021-10-06  9:16   ` Miroslav Benes
2021-10-07  9:18     ` Vasily Gorbik
2021-10-07 10:02       ` Peter Zijlstra
2021-10-13 19:37   ` Arnd Bergmann
2021-10-14 10:42     ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37   ` Paul E. McKenney
2021-09-29 19:09     ` Peter Zijlstra
2021-09-29 19:11     ` Peter Zijlstra
2021-09-29 19:13     ` Peter Zijlstra
2021-09-29 19:24       ` Peter Zijlstra
2021-09-29 19:45         ` Paul E. McKenney
2021-09-29 18:54   ` Peter Zijlstra [this message]
2021-09-29 15:17 ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Peter Zijlstra
2021-10-06  8:12   ` Petr Mladek
2021-10-06  9:04     ` Peter Zijlstra
2021-10-06 10:29       ` Petr Mladek
2021-10-06 11:41         ` Peter Zijlstra
2021-10-06 11:48         ` Miroslav Benes
2021-09-29 15:17 ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Peter Zijlstra
2021-10-06 12:30   ` Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39   ` Marcelo Tosatti
2021-10-21 18:40     ` Marcelo Tosatti
2021-10-21 19:25     ` Peter Zijlstra
2021-10-21 19:57       ` Marcelo Tosatti
2021-10-21 20:18         ` Peter Zijlstra
2021-10-26 18:19           ` Marcelo Tosatti
2021-10-26 19:38             ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney
2021-10-09 10:07 ` [tip: sched/core] sched,livepatch: Use wake_up_if_idle() tip-bot2 for Peter Zijlstra
2021-10-14 11:16 ` tip-bot2 for Peter Zijlstra

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