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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
	Philipp Reisner <philipp.reisner@linbit.com>,
	Bryan Tan <bryantan@vmware.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Eric Dumazet <edumazet@google.com>,
	Bob Pearson <rpearsonhpe@gmail.com>,
	Ariel Levkovich <lariel@nvidia.com>,
	Theodore Ts'o <tytso@mit.edu>, Julian Anastasov <ja@ssi.bg>
Subject: Re: [PATCH 00/13] Rename k[v]free_rcu() single argument to k[v]free_rcu_mightsleep()
Date: Thu, 23 Feb 2023 10:31:24 -0800	[thread overview]
Message-ID: <20230223183124.GF2948950@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <84fd00b0-aa87-e4b7-e0a4-d57b720216c0@kernel.dk>

On Thu, Feb 23, 2023 at 07:57:13AM -0700, Jens Axboe wrote:
> On 2/1/23 8:08 AM, Uladzislau Rezki (Sony) wrote:
> > This small series is based on Paul's "dev" branch. Head is 6002817348a1c610dc1b1c01ff81654cdec12be4
> > it renames a single argument of k[v]free_rcu() to its new k[v]free_rcu_mightsleep() name.
> > 
> > 1.
> > The problem is that, recently we have run into a precedent when
> > a user intended to give a second argument to kfree_rcu() API but
> > forgot to do it in a code so a call became as a single argument
> > of kfree_rcu() API.
> > 
> > 2.
> > Such mistyping can lead to hidden bags where sleeping is forbidden.
> > 
> > 3.
> > _mightsleep() prefix gives much more information for which contexts
> > it can be used for.
> 
> This patchset seems weird to me. We have a LOT of calls that might
> sleep, yet we don't suffix them all with _mightsleep(). Why is this
> any different? Why isn't this just a might_sleep() call in the
> actual helper, which will suffice for checkers and catch it at
> runtime as well.

Fair enough, and the situation that this patchset is addressing is also a
bit unusual.  This change was requested by Eric Dumazet due to a situation
where someone forgot the optional second argument to kfree_rcu().  Now,
you are right that this would be caught if invoked from a non-sleepable
context, but there are also cases where sleeping is legal, but where the
occasional wait for an RCU grace period would be a problem.  The checkers
cannot easily catch this sort of thing, and hence the change in name.

Hey, the combined one/two-argument form seemed like a good idea at
the time!  ;-)

							Thanx, Paul

  reply	other threads:[~2023-02-23 18:31 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-01 15:08 [PATCH 00/13] Rename k[v]free_rcu() single argument to k[v]free_rcu_mightsleep() Uladzislau Rezki (Sony)
2023-02-01 15:08 ` [PATCH 01/13] rcu/kvfree: Add kvfree_rcu_mightsleep() and kfree_rcu_mightsleep() Uladzislau Rezki (Sony)
2023-02-02  7:54   ` Zhuo, Qiuxu
2023-02-02 15:07     ` Paul E. McKenney
2023-02-01 15:08 ` [PATCH 02/13] drbd: Rename kvfree_rcu() to kvfree_rcu_mightsleep() Uladzislau Rezki (Sony)
2023-03-09 13:39   ` Uladzislau Rezki
2023-02-01 15:08 ` [PATCH 03/13] misc: vmw_vmci: " Uladzislau Rezki (Sony)
2023-03-09 13:41   ` Uladzislau Rezki
2023-03-09 14:36   ` Vishnu Dasa
2023-02-01 15:08 ` [PATCH 04/13] tracing: " Uladzislau Rezki (Sony)
2023-03-09 13:45   ` Uladzislau Rezki
2023-03-15 22:36     ` Steven Rostedt
2023-03-15 23:19       ` Jens Axboe
2023-03-16  0:37         ` Paul E. McKenney
2023-03-16  2:23           ` Steven Rostedt
2023-03-16  3:44             ` Paul E. McKenney
2023-03-16  4:16               ` Joel Fernandes
2023-03-16 12:14                 ` Steven Rostedt
2023-03-16 14:56                   ` Paul E. McKenney
2023-03-16  8:16       ` Uladzislau Rezki
2023-03-16 13:56         ` Steven Rostedt
2023-03-16 15:05           ` Uladzislau Rezki
2023-03-17  9:05             ` Uladzislau Rezki
2023-03-16 15:12           ` Paul E. McKenney
2023-03-16 17:54       ` Paul E. McKenney
2023-03-16 17:57       ` Uladzislau Rezki
2023-03-16 18:01         ` Joel Fernandes
2023-03-18 16:11           ` Steven Rostedt
2023-03-22 23:10             ` Joel Fernandes
2023-02-01 15:08 ` [PATCH 05/13] lib/test_vmalloc.c: " Uladzislau Rezki (Sony)
2023-02-01 15:08 ` [PATCH 06/13] net/sysctl: " Uladzislau Rezki (Sony)
2023-03-09 13:48   ` Uladzislau Rezki
2023-03-09 13:49   ` Uladzislau Rezki
2023-02-01 15:08 ` [PATCH 07/13] RDMA/rxe: Rename kfree_rcu() to kfree_rcu_mightsleep() Uladzislau Rezki (Sony)
2023-03-09 13:48   ` Uladzislau Rezki
2023-03-09 14:13     ` Uladzislau Rezki
2023-03-10  0:55       ` Joel Fernandes
2023-03-13 19:43         ` Bob Pearson
2023-03-15 11:50           ` Joel Fernandes
2023-03-15 18:07             ` Bob Pearson
2023-03-14  6:31       ` Zhu Yanjun
2023-02-01 15:08 ` [PATCH 08/13] net/mlx5: " Uladzislau Rezki (Sony)
2023-03-09 13:47   ` Uladzislau Rezki
2023-02-01 15:08 ` [PATCH 09/13] ext4/super: " Uladzislau Rezki (Sony)
2023-03-09 13:43   ` Uladzislau Rezki
2023-02-01 19:12 ` [PATCH 00/13] Rename k[v]free_rcu() single argument to k[v]free_rcu_mightsleep() Paul E. McKenney
2023-02-02 15:54   ` Uladzislau Rezki
2023-02-02 16:35     ` Paul E. McKenney
2023-02-23 12:45 ` Frederic Weisbecker
2023-02-23 14:29   ` Zhuo, Qiuxu
2023-02-23 15:54     ` Paul E. McKenney
2023-02-23 16:21       ` Julian Anastasov
2023-02-23 17:14         ` Paul E. McKenney
2023-02-23 17:36           ` Pablo Neira Ayuso
2023-02-23 18:21             ` Paul E. McKenney
2023-02-23 14:57 ` Jens Axboe
2023-02-23 18:31   ` Paul E. McKenney [this message]
2023-02-23 19:36     ` Jens Axboe
2023-02-23 19:47       ` Paul E. McKenney
2023-02-23 19:57         ` Jens Axboe
2023-03-15 19:14 ` Steven Rostedt
2023-03-15 19:16   ` Jens Axboe
2023-03-15 19:25     ` Uladzislau Rezki
2023-03-15 19:34       ` Steven Rostedt
2023-03-15 19:57         ` Joel Fernandes
2023-03-15 20:28           ` Steven Rostedt
2023-03-15 21:07             ` Uladzislau Rezki
2023-03-15 21:14               ` Uladzislau Rezki
2023-03-15 22:08             ` Joel Fernandes
2023-03-15 22:26               ` Steven Rostedt
2023-03-16  2:13                 ` Joel Fernandes
2023-03-16  2:50                   ` Steven Rostedt
2023-03-16  5:01                     ` Joel Fernandes
2023-03-16  1:25               ` Theodore Ts'o
2023-03-16  2:15                 ` Steven Rostedt
2023-03-16  2:52                 ` Paul E. McKenney
2023-03-16  0:42         ` Theodore Ts'o

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