From: Thomas Gleixner <tglx@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
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 14:27:18 +0100 [thread overview]
Message-ID: <87o8jsnop5.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201120002621.GA32792@lothringen>
On Fri, Nov 20 2020 at 01:26, Frederic Weisbecker wrote:
> 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() ?
It's really only required for local_bh_disable(). Lemme add a comment.
>> + } 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.
Indeed it's pointless.
>> + /*
>> + * 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() ?
Yep.
Thanks,
tglx
next prev parent reply other threads:[~2020-11-20 13:27 UTC|newest]
Thread overview: 38+ 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 ` [patch 01/19] parisc: Remove bogus __IRQ_STAT macro Thomas Gleixner
2020-11-13 14:02 ` [patch 02/19] sh: Get rid of nmi_count() Thomas Gleixner
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 ` [patch 04/19] um/irqstat: Get rid of the duplicated declarations Thomas Gleixner
2020-11-13 14:02 ` [patch 05/19] ARM: irqstat: Get rid of duplicated declaration Thomas Gleixner
2020-11-13 14:02 ` [patch 06/19] arm64: " Thomas Gleixner
2020-11-16 10:01 ` Will Deacon
2020-11-16 10:51 ` Marc Zyngier
2020-11-13 14:02 ` [patch 07/19] asm-generic/irqstat: Add optional __nmi_count member 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 ` [patch 09/19] irqstat: Move declaration into asm-generic/hardirq.h Thomas Gleixner
2020-11-13 14:02 ` [patch 10/19] preempt: Cleanup the macro maze a bit Thomas Gleixner
2020-11-16 12:17 ` Peter Zijlstra
2020-11-16 17:42 ` Thomas Gleixner
2020-11-13 14:02 ` [patch 11/19] softirq: Move related code into one section Thomas Gleixner
2020-11-19 12:20 ` Frederic Weisbecker
2020-11-13 14:02 ` [patch 12/19] softirq: Add RT specific softirq accounting Thomas Gleixner
2020-11-19 12:18 ` Frederic Weisbecker
2020-11-19 18:34 ` Thomas Gleixner
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 ` [patch 14/19] softirq: Make softirq control and processing RT aware Thomas Gleixner
2020-11-20 0:26 ` Frederic Weisbecker
2020-11-20 13:27 ` Thomas Gleixner [this message]
2020-11-23 13:44 ` Frederic Weisbecker
2020-11-23 19:27 ` Thomas Gleixner
2020-11-23 19:56 ` Frederic Weisbecker
2020-11-23 23:58 ` Frederic Weisbecker
2020-11-24 0:06 ` Thomas Gleixner
2020-11-24 0:13 ` Frederic Weisbecker
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 ` [patch 16/19] rcu: Prevent false positive softirq warning " 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 ` [patch 18/19] tasklets: Use static inlines for stub implementations Thomas Gleixner
2020-11-13 14:02 ` [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT Thomas Gleixner
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