linux-kernel - Re: [PATCH tip/core/rcu 06/19] rcu: Add warning to detect half-interrupts

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Message-Id: <20190313155155.GN13351@linux.ibm.com>
Date:   Wed, 13 Mar 2019 08:51:55 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        luto@...nel.org, byungchul.park@....com
Subject: Re: [PATCH tip/core/rcu 06/19] rcu: Add warning to detect
 half-interrupts

On Wed, Mar 13, 2019 at 11:27:26AM -0400, Steven Rostedt wrote:
> On Wed, 13 Mar 2019 11:09:48 -0400
> Joel Fernandes <joel@...lfernandes.org> wrote:
> 
> > AFAICS, lockdep does not specifically track when we enter an interrupt, but
> > rather only tracks when interrupts are enabled/disabled.
> 
> It does:
> 
> #define __irq_enter()					\
> 	do {						\
> 		account_irq_enter_time(current);	\
> 		preempt_count_add(HARDIRQ_OFFSET);	\
> 		trace_hardirq_enter();			\
> 	} while (0)
> 
> # define trace_hardirq_enter()			\
> do {						\
> 	current->hardirq_context++;		\
> } while (0)
> 
> 
> And if the hardirq_context ever does not match "in_irq()" lockdep will
> complain loudly.

Good to know, thank you!

Does this mean that there is a better approach that Joel's suggestion?
I believe he would end up with something like this:

	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && !in_irq());

It would be nice if there is something like this:

	lockdep_assert_in_irq_handler();

But I haven't seen this.  (Not that I have looked particularly hard for
such a thing, mind you!)

							Thanx, Paul