linux-kernel - [PATCH 0/3] introduce task_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:	Mon, 27 Oct 2014 20:53:39 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <ktkhai@...allels.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Kirill Tkhai <tkhai@...dex.ru>,
	Christoph Lameter <cl@...ux.com>
Subject: [PATCH 0/3] introduce task_rcu_dereference()

Peter, let me repeat once again, if you still prefer to avoid
probe_slab_address() and use SLAB_DESTROY_BY_RCU I won't argue.

I do not like SLAB_DESTROY_BY_RCU in this particular case. With
or without SDBR rq->curr can be reused and we need to avoid this
race. The fact that with SDBR it can be reused only as another
instance of task_struct is absolutely immaterial imo.

Not to mention that SDBR still adds some overhead while probe_slab()
is free unless CONFIG_DEBUG_PAGEALLOC, but this option adds a large
slowdown anyway.

However, my arguments against SDBR are not strictly technical, and
I think that this falls into "maintainer is always right" category.

So please tell me if you prefer v2 with SDBR. In this case 2/3 is
not needed, and 3/3 can simply read ->sighand. Otherwise the code
(and even the comments) will be the same.

Compared to the draft patch I sent before

	- update the comments

	- do not use ERR_PTR(), just return the task or NULL, so
	  kernel/sched/ doesn't need another helper.

	  This means that task_rcu_dereference() does retry itself.
	  We can add __task_rcu_dereference() if we have another
	  which do not need/want to retry.

Oleg.

 include/linux/sched.h   |    1 +
 include/linux/uaccess.h |   30 +++++++++++++++-------------
 kernel/exit.c           |   49 +++++++++++++++++++++++++++++++++++++++++++++++
 mm/slub.c               |    6 +----
 4 files changed, 67 insertions(+), 19 deletions(-)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/