linux-kernel - Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu

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Message-ID: <20200523150831.wdrthklakwm6wago@linutronix.de>
Date:   Sat, 23 May 2020 17:08:31 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org
Subject: Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data
 access

On 2020-05-22 10:39:53 [-0700], Paul E. McKenney wrote:
> It looks good to me, but I have not yet tested it.  (Happy to let you
> take the first crack at rcutorture in any case, scenarios SRCU-P and
> SRCU-N.)

on it.

> > That check_init_srcu_struct() is needed, because otherwise:
> > 
> > | BUG: spinlock bad magic on CPU#2, swapper/0/1
> > |  lock: 0xffff88803ed28ac0, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
> > | CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc6+ #81
> > | Call Trace:
> > |  dump_stack+0x71/0xa0
> > |  do_raw_spin_lock+0x6c/0xb0
> > |  _raw_spin_lock_irqsave+0x33/0x40
> > |  synchronize_srcu+0x24/0xc9
> > |  wakeup_source_remove+0x4d/0x70
> > |  wakeup_source_unregister.part.0+0x9/0x40
> > |  device_wakeup_enable+0x99/0xc0
> > 
> > I'm not sure if there should be an explicit init of `wakeup_srcu' or if
> > an srcu function (like call_srcu()) is supposed to do it.
> 
> It is fine.  Beforehand, that check_init_srcu_struct() would have been
> invoked very shortly thereafter from __call_srcu(), and there is no
> instead harm invoking it a few microseconds earlier.  ;-)

Oki. I wasn't sure if an explizit initialized on wakeup_srcu's side was
missing or if this is new since we use the lock earlier.

>  							Thanx, Paul

Sebastian