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

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Message-ID: <20190313112726.01d974fc@gandalf.local.home>
Date:   Wed, 13 Mar 2019 11:27:26 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        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, 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.

-- Steve