linux-kernel - Re: [PATCH v2] drivers/md: use proper rcu accessor

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Message-ID: <20141124040903.GB595@redhat.com>
Date:	Sun, 23 Nov 2014 23:09:04 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Pranith Kumar <bobby.prani@...il.com>, dm-devel@...hat.com,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>, dvhart@...ux.intel.com,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v2] drivers/md: use proper rcu accessor

On Sun, Nov 23 2014 at 12:34pm -0500,
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> rcu_dereference() should be used in sections protected by rcu_read_lock.
> 
> For writers, holding some kind of mutex or lock,
> rcu_dereference_protected() is the way to go, adding explicit lockdep
> bits.
> 
> In __unbind(), we are the last user of this mapped device, so can use
> the constant '1' instead of a lockdep_is_held(), not consistent with
> other uses of rcu_dereference_protected() which use md->suspend_lock
> mutex.
> 
> Reported-by: Kirill A. Shutemov <kirill@...temov.name>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Fixes: 33423974bfc1 ("dm: Use rcu_dereference() for accessing rcu pointer")
> Cc: Pranith Kumar <bobby.prani@...il.com>
> Cc: Mike Snitzer <snitzer@...hat.com>

Thanks, I've staged this for 3.19:
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-3.19&id=a12f5d48bdfeb5fe10157ac01c3de29269f457c6
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