linux-kernel - Re: [PATCH 00/13] Rename k[v]free_rcu() single argument to k[v]free_rcu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 23 Feb 2023 10:31:24 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Bryan Tan <bryantan@...are.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Bob Pearson <rpearsonhpe@...il.com>,
        Ariel Levkovich <lariel@...dia.com>,
        Theodore Ts'o <tytso@....edu>, Julian Anastasov <ja@....bg>
Subject: Re: [PATCH 00/13] Rename k[v]free_rcu() single argument to
 k[v]free_rcu_mightsleep()

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