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From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Paul McKenney <paulmck@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Arnd Bergmann <arnd@arndb.de>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Helge Deller <deller@gmx.de>,
	linux-parisc@vger.kernel.org,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	linux-sh@vger.kernel.org, Jeff Dike <jdike@addtoit.com>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-um@lists.infradead.org,
	Russell King <linux@armlinux.org.uk>,
	Marc Zyngier <maz@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [patch 14/19] softirq: Make softirq control and processing RT aware
Date: Fri, 20 Nov 2020 01:26:21 +0100	[thread overview]
Message-ID: <20201120002621.GA32792@lothringen> (raw)
In-Reply-To: <20201113141734.324061522@linutronix.de>

On Fri, Nov 13, 2020 at 03:02:21PM +0100, Thomas Gleixner wrote:
> +void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
> +{
> +	unsigned long flags;
> +	int newcnt;
> +
> +	WARN_ON_ONCE(in_hardirq());
> +
> +	/* First entry of a task into a BH disabled section? */
> +	if (!current->softirq_disable_cnt) {
> +		if (preemptible()) {
> +			local_lock(&softirq_ctrl.lock);
> +			rcu_read_lock();

Ah you lock RCU because local_bh_disable() implies it and
since it doesn't disable preemption anymore, you must do it
explicitly?

Perhaps local_lock() should itself imply rcu_read_lock() ?

> +		} else {
> +			DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
> +		}
> +	}
> +
> +	preempt_disable();

Do you really need to disable preemption here? Migration is disabled by local_lock()
and I can't figure out a scenario where the below can conflict with a preempting task.

> +	/*
> +	 * Track the per CPU softirq disabled state. On RT this is per CPU
> +	 * state to allow preemption of bottom half disabled sections.
> +	 */
> +	newcnt = this_cpu_add_return(softirq_ctrl.cnt, cnt);

__this_cpu_add_return() ?

> +	/*
> +	 * Reflect the result in the task state to prevent recursion on the
> +	 * local lock and to make softirq_count() & al work.
> +	 */
> +	current->softirq_disable_cnt = newcnt;
> +
> +	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
> +		raw_local_irq_save(flags);
> +		lockdep_softirqs_off(ip);
> +		raw_local_irq_restore(flags);
> +	}
> +	preempt_enable();
> +}
> +EXPORT_SYMBOL(__local_bh_disable_ip);
> +
> +static void __local_bh_enable(unsigned int cnt, bool unlock)
> +{
> +	unsigned long flags;
> +	int newcnt;
> +
> +	DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=
> +			    this_cpu_read(softirq_ctrl.cnt));

__this_cpu_read() ? Although that's lockdep only so not too important.

> +
> +	preempt_disable();

Same question about preempt_disable().

> +	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) {
> +		raw_local_irq_save(flags);
> +		lockdep_softirqs_on(_RET_IP_);
> +		raw_local_irq_restore(flags);
> +	}
> +
> +	newcnt = this_cpu_sub_return(softirq_ctrl.cnt, cnt);

__this_cpu_sub_return?

> +	current->softirq_disable_cnt = newcnt;
> +	preempt_enable();
> +
> +	if (!newcnt && unlock) {
> +		rcu_read_unlock();
> +		local_unlock(&softirq_ctrl.lock);
> +	}
> +}

Thanks.

WARNING: multiple messages have this Message-ID
From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Rich Felker <dalias@libc.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Paul McKenney <paulmck@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	linux-sh@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Richard Weinberger <richard@nod.at>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Jeff Dike <jdike@addtoit.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	linux-parisc@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	linux-um@lists.infradead.org, Will Deacon <will@kernel.org>,
	Helge Deller <deller@gmx.de>,
	linux-arm-kernel@lists.infradead.org,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>
Subject: Re: [patch 14/19] softirq: Make softirq control and processing RT aware
Date: Fri, 20 Nov 2020 01:26:21 +0100	[thread overview]
Message-ID: <20201120002621.GA32792@lothringen> (raw)
In-Reply-To: <20201113141734.324061522@linutronix.de>

On Fri, Nov 13, 2020 at 03:02:21PM +0100, Thomas Gleixner wrote:
> +void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
> +{
> +	unsigned long flags;
> +	int newcnt;
> +
> +	WARN_ON_ONCE(in_hardirq());
> +
> +	/* First entry of a task into a BH disabled section? */
> +	if (!current->softirq_disable_cnt) {
> +		if (preemptible()) {
> +			local_lock(&softirq_ctrl.lock);
> +			rcu_read_lock();

Ah you lock RCU because local_bh_disable() implies it and
since it doesn't disable preemption anymore, you must do it
explicitly?

Perhaps local_lock() should itself imply rcu_read_lock() ?

> +		} else {
> +			DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
> +		}
> +	}
> +
> +	preempt_disable();

Do you really need to disable preemption here? Migration is disabled by local_lock()
and I can't figure out a scenario where the below can conflict with a preempting task.

> +	/*
> +	 * Track the per CPU softirq disabled state. On RT this is per CPU
> +	 * state to allow preemption of bottom half disabled sections.
> +	 */
> +	newcnt = this_cpu_add_return(softirq_ctrl.cnt, cnt);

__this_cpu_add_return() ?

> +	/*
> +	 * Reflect the result in the task state to prevent recursion on the
> +	 * local lock and to make softirq_count() & al work.
> +	 */
> +	current->softirq_disable_cnt = newcnt;
> +
> +	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
> +		raw_local_irq_save(flags);
> +		lockdep_softirqs_off(ip);
> +		raw_local_irq_restore(flags);
> +	}
> +	preempt_enable();
> +}
> +EXPORT_SYMBOL(__local_bh_disable_ip);
> +
> +static void __local_bh_enable(unsigned int cnt, bool unlock)
> +{
> +	unsigned long flags;
> +	int newcnt;
> +
> +	DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=
> +			    this_cpu_read(softirq_ctrl.cnt));

__this_cpu_read() ? Although that's lockdep only so not too important.

> +
> +	preempt_disable();

Same question about preempt_disable().

> +	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) {
> +		raw_local_irq_save(flags);
> +		lockdep_softirqs_on(_RET_IP_);
> +		raw_local_irq_restore(flags);
> +	}
> +
> +	newcnt = this_cpu_sub_return(softirq_ctrl.cnt, cnt);

__this_cpu_sub_return?

> +	current->softirq_disable_cnt = newcnt;
> +	preempt_enable();
> +
> +	if (!newcnt && unlock) {
> +		rcu_read_unlock();
> +		local_unlock(&softirq_ctrl.lock);
> +	}
> +}

Thanks.

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  reply	other threads:[~2020-11-20  0:26 UTC|newest]

Thread overview: 115+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13 14:02 [patch 00/19] softirq: Cleanups and RT awareness Thomas Gleixner
2020-11-13 14:02 ` Thomas Gleixner
2020-11-13 14:02 ` Thomas Gleixner
2020-11-13 14:02 ` [patch 01/19] parisc: Remove bogus __IRQ_STAT macro Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 02/19] sh: Get rid of nmi_count() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2021-01-01 14:27   ` [patch 02/19] " John Paul Adrian Glaubitz
2021-01-01 14:27     ` John Paul Adrian Glaubitz
2020-11-13 14:02 ` [patch 03/19] irqstat: Get rid of nmi_count() and __IRQ_STAT() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 04/19] um/irqstat: Get rid of the duplicated declarations Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 05/19] ARM: irqstat: Get rid of duplicated declaration Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 18:19   ` Valentin Schneider
2020-11-16 18:19     ` Valentin Schneider
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 06/19] arm64: " Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 10:01   ` Will Deacon
2020-11-16 10:01     ` Will Deacon
2020-11-16 10:01     ` Will Deacon
2020-11-16 10:51   ` Marc Zyngier
2020-11-16 10:51     ` Marc Zyngier
2020-11-16 10:51     ` Marc Zyngier
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 07/19] asm-generic/irqstat: Add optional __nmi_count member Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 08/19] sh: irqstat: Use the generic irq_cpustat_t Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 09/19] irqstat: Move declaration into asm-generic/hardirq.h Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 10/19] preempt: Cleanup the macro maze a bit Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 12:17   ` Peter Zijlstra
2020-11-16 12:17     ` Peter Zijlstra
2020-11-16 12:17     ` Peter Zijlstra
2020-11-16 17:42     ` Thomas Gleixner
2020-11-16 17:42       ` Thomas Gleixner
2020-11-16 17:42       ` Thomas Gleixner
2020-11-17 10:21       ` Peter Zijlstra
2020-11-17 10:21         ` Peter Zijlstra
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 11/19] softirq: Move related code into one section Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-19 12:20   ` Frederic Weisbecker
2020-11-19 12:20     ` Frederic Weisbecker
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 12/19] softirq: Add RT specific softirq accounting Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-19 12:18   ` Frederic Weisbecker
2020-11-19 12:18     ` Frederic Weisbecker
2020-11-19 18:34     ` Thomas Gleixner
2020-11-19 18:34       ` Thomas Gleixner
2020-11-19 22:52       ` Frederic Weisbecker
2020-11-19 22:52         ` Frederic Weisbecker
2020-11-13 14:02 ` [patch 13/19] softirq: Move various protections into inline helpers Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 14/19] softirq: Make softirq control and processing RT aware Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-20  0:26   ` Frederic Weisbecker [this message]
2020-11-20  0:26     ` Frederic Weisbecker
2020-11-20 13:27     ` Thomas Gleixner
2020-11-20 13:27       ` Thomas Gleixner
2020-11-23 13:44   ` Frederic Weisbecker
2020-11-23 13:44     ` Frederic Weisbecker
2020-11-23 19:27     ` Thomas Gleixner
2020-11-23 19:27       ` Thomas Gleixner
2020-11-23 19:56       ` Frederic Weisbecker
2020-11-23 19:56         ` Frederic Weisbecker
2020-11-23 23:58       ` Frederic Weisbecker
2020-11-23 23:58         ` Frederic Weisbecker
2020-11-24  0:06         ` Thomas Gleixner
2020-11-24  0:06           ` Thomas Gleixner
2020-11-24  0:13           ` Frederic Weisbecker
2020-11-24  0:13             ` Frederic Weisbecker
2020-11-24  0:22             ` Thomas Gleixner
2020-11-24  0:22               ` Thomas Gleixner
2020-11-13 14:02 ` [patch 15/19] tick/sched: Prevent false positive softirq pending warnings on RT Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 16/19] rcu: Prevent false positive softirq warning " Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 17/19] softirq: Replace barrier() with cpu_relax() in tasklet_unlock_wait() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 18/19] tasklets: Use static inlines for stub implementations Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner

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