From: Jan Kara <jack@suse.cz>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Christoph Lameter <cl@linux.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Pablo Neira Ayuso <pablo@netfilter.org>,
Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
Florian Westphal <fw@strlen.de>,
David Miller <davem@davemloft.net>,
NetFilter <netfilter-devel@vger.kernel.org>,
coreteam@netfilter.org,
Network Development <netdev@vger.kernel.org>,
Gerrit Renker <gerrit@erg.abdn.ac.uk>,
dccp@vger.kernel.org, Jani Nikula <jani.nikula@linux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
Dave Airlie <airlied@linux.ie>,
intel-gfx <intel-gfx@lists.freedesktop.org>,
DRI <dri-devel@lists.freedesktop.org>,
Eric Dumazet <edumazet@google.com>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
Ursula Braun <ubraun@linux.ibm.com>,
linux-s390 <linux-s390@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
Andrey Konovalov <andreyknvl@google.com>
Subject: Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4 13/17] khwasan: add hooks implementation)
Date: Mon, 6 Aug 2018 22:20:17 +0200 [thread overview]
Message-ID: <20180806202017.lrzihv42b4mtcgrn@quack2.suse.cz> (raw)
In-Reply-To: <CACT4Y+aYZumcc-Od5T1AnP4mwn8-FaWfxvfb93MnNwQPqG8TDw@mail.gmail.com>
On Wed 01-08-18 10:46:35, Dmitry Vyukov wrote:
> I guess it would be useful to have such extensive comment for each
> SLAB_TYPESAFE_BY_RCU use explaining why it is needed and how all the
> tricky aspects are handled.
>
> For example, the one in jbd2 is interesting because it memsets the
> whole object before freeing it into SLAB_TYPESAFE_BY_RCU slab:
>
> memset(jh, JBD2_POISON_FREE, sizeof(*jh));
> kmem_cache_free(jbd2_journal_head_cache, jh);
>
> I guess there are also tricky ways how it can all work in the end
> (type-stable state is only a byte, or we check for all possible
> combinations of being overwritten with JBD2_POISON_FREE). But at first
> sight it does look fishy.
The RCU access is used from a single place:
fs/jbd2/transaction.c: jbd2_write_access_granted()
There are also quite some comments explaining why what it does is safe. The
overwrite by JBD2_POISON_FREE is much older than this RCU stuff (honestly I
didn't know about it until this moment) and has nothing to do with the
safety of RCU access.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2018-08-06 20:20 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-31 17:01 Andrey Ryabinin
2018-07-31 17:09 ` Florian Westphal
2018-07-31 17:32 ` Eric Dumazet
2018-07-31 17:36 ` Christopher Lameter
2018-07-31 17:41 ` Eric Dumazet
2018-07-31 17:51 ` Dmitry Vyukov
2018-07-31 18:16 ` Eric Dumazet
2018-07-31 17:49 ` Linus Torvalds
2018-07-31 18:51 ` Linus Torvalds
2018-08-01 8:46 ` Dmitry Vyukov
2018-08-01 9:10 ` Dmitry Vyukov
2018-08-01 10:35 ` Florian Westphal
2018-08-01 10:41 ` Dmitry Vyukov
2018-08-01 11:40 ` Florian Westphal
2018-08-01 12:38 ` Dmitry Vyukov
2018-08-01 13:46 ` Florian Westphal
2018-08-01 13:52 ` Dmitry Vyukov
2018-08-06 20:20 ` Jan Kara [this message]
2018-08-01 9:03 ` Andrey Ryabinin
2018-08-01 10:23 ` Eric Dumazet
2018-08-01 10:34 ` Dmitry Vyukov
2018-08-01 11:28 ` Eric Dumazet
2018-08-01 11:35 ` Dmitry Vyukov
2018-08-01 15:15 ` Christopher Lameter
2018-08-01 15:37 ` Eric Dumazet
2018-08-01 15:51 ` Misuse of constructors Matthew Wilcox
2018-08-01 15:53 ` SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4 13/17] khwasan: add hooks implementation) Dmitry Vyukov
2018-08-01 16:22 ` Christopher Lameter
2018-08-01 16:25 ` Eric Dumazet
2018-08-01 16:47 ` Dmitry Vyukov
2018-08-01 17:18 ` Eric Dumazet
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