From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: paulmck <paulmck@kernel.org>
Cc: rcu <rcu@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
dipankar <dipankar@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
rostedt <rostedt@goodmis.org>,
David Howells <dhowells@redhat.com>,
Eric Dumazet <edumazet@google.com>, fweisbec <fweisbec@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
"Joel Fernandes, Google" <joel@joelfernandes.org>,
Bart Van Assche <bart.vanassche@wdc.com>,
Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
Johannes Thumshirn <jthumshirn@suse.de>,
Shane M Seymour <shane.seymour@hpe.com>,
Martin <martin.petersen@oracle.com>
Subject: Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace()
Date: Thu, 3 Oct 2019 12:35:30 -0400 (EDT) [thread overview]
Message-ID: <644598334.955.1570120530976.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20191003014310.13262-1-paulmck@kernel.org>
----- On Oct 2, 2019, at 9:43 PM, paulmck paulmck@kernel.org wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> Although the rcu_swap_protected() macro follows the example of swap(),
> the interactions with RCU make its update of its argument somewhat
> counter-intuitive. This commit therefore introduces an rcu_replace()
> that returns the old value of the RCU pointer instead of doing the
> argument update. Once all the uses of rcu_swap_protected() are updated
> to instead use rcu_replace(), rcu_swap_protected() will be removed.
We expose the rcu_xchg_pointer() API in liburcu (Userspace RCU) project.
Any reason for not going that way and keep the kernel and user-space RCU
APIs alike ?
It's of course fine if they diverge, but we might want to at least consider
if using the same API name would be OK.
Thanks,
Mathieu
>
> Link:
> https://lore.kernel.org/lkml/CAHk-=wiAsJLw1egFEE=Z7-GGtM6wcvtyytXZA1+BHqta4gg6Hw@mail.gmail.com/
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Cc: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Cc: Shane M Seymour <shane.seymour@hpe.com>
> Cc: Martin K. Petersen <martin.petersen@oracle.com>
> ---
> include/linux/rcupdate.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 75a2ede..3b73287 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -383,6 +383,24 @@ do { \
> } while (0)
>
> /**
> + * rcu_replace() - replace an RCU pointer, returning its old value
> + * @rcu_ptr: RCU pointer, whose old value is returned
> + * @ptr: regular pointer
> + * @c: the lockdep conditions under which the dereference will take place
> + *
> + * Perform a replacement, where @rcu_ptr is an RCU-annotated
> + * pointer and @c is the lockdep argument that is passed to the
> + * rcu_dereference_protected() call used to read that pointer. The old
> + * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
> + */
> +#define rcu_replace(rcu_ptr, ptr, c) \
> +({ \
> + typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
> + rcu_assign_pointer((rcu_ptr), (ptr)); \
> + __tmp; \
> +})
> +
> +/**
> * rcu_swap_protected() - swap an RCU and a regular pointer
> * @rcu_ptr: RCU pointer
> * @ptr: regular pointer
> --
> 2.9.5
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2019-10-03 17:08 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 1:41 [PATCH tip/core/rcu 0/9] Replace rcu_swap_protected() for v5.5 Paul E. McKenney
2019-10-03 1:43 ` [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace() paulmck
2019-10-03 16:35 ` Mathieu Desnoyers [this message]
2019-10-03 16:52 ` Paul E. McKenney
2019-10-03 17:21 ` Mathieu Desnoyers
2019-10-03 19:09 ` Paul E. McKenney
2019-10-03 19:14 ` Mathieu Desnoyers
2019-10-03 1:43 ` [PATCH tip/core/rcu 2/9] x86/kvm/pmu: Replace rcu_swap_protected() with rcu_replace() paulmck
2019-10-03 10:14 ` Paolo Bonzini
2019-10-05 16:11 ` Paul E. McKenney
2019-10-03 1:43 ` [PATCH tip/core/rcu 3/9] drivers/gpu: " paulmck
2019-10-03 1:43 ` [PATCH tip/core/rcu 4/9] drivers/scsi: " paulmck
2019-10-04 2:09 ` Martin K. Petersen
2019-10-05 16:06 ` Paul E. McKenney
2019-10-10 2:36 ` Martin K. Petersen
2019-10-03 1:43 ` [PATCH tip/core/rcu 5/9] fs/afs: " paulmck
2019-10-03 1:43 ` [PATCH tip/core/rcu 6/9] bpf/cgroup: " paulmck
2019-10-03 17:21 ` Andrii Nakryiko
2019-10-03 20:58 ` Song Liu
2019-10-05 16:11 ` Paul E. McKenney
2019-10-03 1:43 ` [PATCH tip/core/rcu 7/9] net/core: " paulmck
2019-10-03 1:43 ` [PATCH tip/core/rcu 8/9] net/netfilter: " paulmck
2019-10-08 14:16 ` Pablo Neira Ayuso
2019-10-09 15:36 ` Paul E. McKenney
2019-10-03 1:43 ` [PATCH tip/core/rcu 9/9] net/sched: " paulmck
2019-10-03 8:38 ` [PATCH tip/core/rcu 5/9] fs/afs: " David Howells
2019-10-05 16:10 ` Paul E. McKenney
2019-10-03 8:39 ` [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace() David Howells
2019-10-03 13:08 ` Steven Rostedt
2019-10-03 13:33 ` Paul E. McKenney
2019-10-03 13:41 ` Peter Zijlstra
2019-10-03 13:58 ` Paul E. McKenney
2019-10-03 14:01 ` Joel Fernandes
2019-10-03 16:31 ` Mathieu Desnoyers
2019-10-03 18:05 ` Peter Zijlstra
2019-10-22 19:11 ` [PATCH v2 tip/core/rcu 0/10] Replace rcu_swap_protected() for v5.5 Paul E. McKenney
2019-10-22 19:12 ` [PATCH tip/core/rcu 01/10] rcu: Upgrade rcu_swap_protected() to rcu_replace() paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 02/10] x86/kvm/pmu: Replace rcu_swap_protected() with rcu_replace() paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 03/10] drivers/gpu: " paulmck
2019-10-28 12:57 ` Joonas Lahtinen
2019-10-28 13:40 ` Paul E. McKenney
2019-10-22 19:12 ` [PATCH tip/core/rcu 04/10] drivers/scsi: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 05/10] fs/afs: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 06/10] bpf/cgroup: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 07/10] net/core: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 08/10] net/netfilter: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 09/10] net/sched: " paulmck
2019-10-22 19:12 ` [PATCH tip/core/rcu 10/10] security/safesetid: " paulmck
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