linux-kernel - Re: Security/cgroup suspicious RCU usage with v4.2-2744-g65a99597f044

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Date:	Tue, 1 Sep 2015 12:37:32 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	Josh Boyer <jwboyer@...oraproject.org>
Cc:	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org
Subject: Re: Security/cgroup suspicious RCU usage with v4.2-2744-g65a99597f044

On Tue, Sep 1, 2015 at 12:21 PM, Josh Boyer <jwboyer@...oraproject.org> wrote:
> Hi All,
>
> All of my test machines hit the backtrace below with Linus' tree as of
> this morning.  Any ideas?

It looks like you are seeing the same as below:

 * https://lkml.org/lkml/2015/8/31/440

> [  +0.160966] ===============================
> [  +0.000001] [ INFO: suspicious RCU usage. ]
> [  +0.000002] 4.3.0-0.rc0.git1.1.fc24.x86_64 #1 Not tainted
> [  +0.000001] -------------------------------
> [  +0.000002] security/device_cgroup.c:405 device_cgroup:verify_new_ex
> called without proper synchronization!
> [  +0.000000]
>               other info that might help us debug this:
>
> [  +0.000001]
>               rcu_scheduler_active = 1, debug_locks = 0
> [  +0.000002] 4 locks held by systemd/1:
> [  +0.000010]  #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff81267f87>]
> vfs_write+0x187/0x1a0
> [  +0.000006]  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff812f3996>]
> kernfs_fop_write+0x66/0x190
> [  +0.000005]  #2:  (s_active#61){++++.+}, at: [<ffffffff812f399e>]
> kernfs_fop_write+0x6e/0x190
> [  +0.000007]  #3:  (devcgroup_mutex){+.+...}, at:
> [<ffffffff813ada3c>] devcgroup_access_write+0x3c/0x6e0
> [  +0.000000]
>               stack backtrace:
> [  +0.000003] CPU: 3 PID: 1 Comm: systemd Not tainted
> 4.3.0-0.rc0.git1.1.fc24.x86_64 #1
> [  +0.000001] Hardware name:                  /D34010WYK, BIOS
> WYLPT10H.86A.0026.2014.0514.1714 05/14/2014
> [  +0.000004]  0000000000000000 000000006dc9945a ffff88040ce73c68
> ffffffff8184e49c
> [  +0.000003]  0000000000000000 ffff88040cdd4000 ffff88040ce73c98
> ffffffff81101437
> [  +0.000003]  ffff880408646d00 ffff88040ce73d00 0000000000000002
> 0000000000000001
> [  +0.000001] Call Trace:
> [  +0.000006]  [<ffffffff8184e49c>] dump_stack+0x4c/0x65
> [  +0.000004]  [<ffffffff81101437>] lockdep_rcu_suspicious+0xd7/0x110
> [  +0.000004]  [<ffffffff813ad6e8>] verify_new_ex+0xd8/0xe0
> [  +0.000003]  [<ffffffff813addaf>] devcgroup_access_write+0x3af/0x6e0
> [  +0.000005]  [<ffffffff81023999>] ? sched_clock+0x9/0x10
> [  +0.000004]  [<ffffffff811599e4>] cgroup_file_write+0x44/0x1e0
> [  +0.000003]  [<ffffffff812f3a71>] kernfs_fop_write+0x141/0x190
> [  +0.000002]  [<ffffffff81267497>] __vfs_write+0x37/0x100
> [  +0.000002]  [<ffffffff81267f87>] ? vfs_write+0x187/0x1a0
> [  +0.000004]  [<ffffffff8138929d>] ? security_file_permission+0x3d/0xc0
> [  +0.000002]  [<ffffffff81267ea9>] vfs_write+0xa9/0x1a0
> [  +0.000003]  [<ffffffff81268bc8>] SyS_write+0x58/0xd0
> [  +0.000004]  [<ffffffff818580ee>] entry_SYSCALL_64_fastpath+0x12/0x76
> --
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-- 
paul moore
www.paul-moore.com
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