From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
"Paul E. McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Joel Fernandes <joel@joelfernandes.org>,
John Ogness <john.ogness@linutronix.de>,
Josh Triplett <josh@joshtriplett.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Waiman Long <longman@redhat.com>, Will Deacon <will@kernel.org>,
Zqiang <qiang.zhang1211@gmail.com>
Subject: Re: [RFC PATCH] srcu: Use try-lock lockdep annotation for NMI-safe access.
Date: Thu, 28 Sep 2023 08:33:50 +0200 [thread overview]
Message-ID: <20230928063350.KveBSZGg@linutronix.de> (raw)
In-Reply-To: <ZRUX0YUrXfepRGKE@Boquns-Mac-mini.home>
On 2023-09-27 23:06:09 [-0700], Boqun Feng wrote:
> SRCU only has read lock usage from lockdep PoV, but after that commit,
> we annotate synchronize_srcu() as a write lock usage, so that we can
> detect deadlocks between *normal* srcu_read_lock() and
> synchronize_srcu(), however the side effect is now SRCU has a write lock
> usage from lockdep PoV.
Ach. There is a write annotation for SRCU and RCU has none. Okay that
explains it.
> Actually in the above commit, I explicitly leave
> srcu_read_lock_nmisafe() alone since its locking rules may be different
> compared to srcu_read_lock(). In lockdep terms, srcu_read_lock_nmisafe()
> is a !check read lock and srcu_read_lock() is a check read lock.
This was on v6.6-rc3 so it has the commit f0f44752f5f61 ("rcu: Annotate
SRCU's update-side lockdep dependencies").
> Maybe
> instead of using the trylock trick, we change lockdep to igore !check
> locks for NMI context detection? Untested code as below:
Just tested, no splat for the SRCU-in-NMI usage.
Sebastian
next prev parent reply other threads:[~2023-09-28 6:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-27 16:02 Sebastian Andrzej Siewior
2023-09-28 6:06 ` Boqun Feng
2023-09-28 6:33 ` Sebastian Andrzej Siewior [this message]
2023-09-28 8:05 ` Peter Zijlstra
2023-09-28 8:09 ` Peter Zijlstra
2023-09-28 14:54 ` Boqun Feng
2023-09-28 15:29 ` Peter Zijlstra
2023-09-28 17:09 ` Boqun Feng
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