From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Tejun Heo <tj@kernel.org>
Cc: Felipe Balbi <balbi@ti.com>,
James Morris <james.l.morris@oracle.com>,
serge@hallyn.com, linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org,
Linux OMAP Mailing List <linux-omap@vger.kernel.org>
Subject: Re: [PATCH v2] security: device_cgroup: fix RCU lockdep splat
Date: Wed, 2 Sep 2015 17:14:33 -0700 [thread overview]
Message-ID: <20150903001433.GB4029@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150902162450.GJ22326@mtj.duckdns.org>
On Wed, Sep 02, 2015 at 12:24:50PM -0400, Tejun Heo wrote:
> cc'ing Paul.
>
> On Wed, Sep 02, 2015 at 08:12:28AM -0500, Felipe Balbi wrote:
> > while booting AM437x device, the following splat
> > triggered:
> >
> > [ 12.005238] ===============================
> > [ 12.009749] [ INFO: suspicious RCU usage. ]
> > [ 12.014116] 4.2.0-next-20150831 #1154 Not tainted
> > [ 12.019050] -------------------------------
> > [ 12.023408] security/device_cgroup.c:405 device_cgroup:verify_new_ex called without proper synchronization!
> ...
> > [ 12.128326] [<c0317a04>] (verify_new_ex) from [<c0317f50>] (devcgroup_access_write+0x374/0x658)
> > [ 12.137426] [<c0317f50>] (devcgroup_access_write) from [<c00d2800>] (cgroup_file_write+0x28/0x1bc)
> > [ 12.146796] [<c00d2800>] (cgroup_file_write) from [<c01f1670>] (kernfs_fop_write+0xc0/0x1b8)
> > [ 12.155620] [<c01f1670>] (kernfs_fop_write) from [<c0177c94>] (__vfs_write+0x1c/0xd8)
> > [ 12.163783] [<c0177c94>] (__vfs_write) from [<c0178594>] (vfs_write+0x90/0x16c)
> > [ 12.171426] [<c0178594>] (vfs_write) from [<c0178db4>] (SyS_write+0x44/0x9c)
> > [ 12.178806] [<c0178db4>] (SyS_write) from [<c000f680>] (ret_fast_syscall+0x0/0x1c)
>
> This shouldn't be happening because devcgroup_access_write() always
> grabs devcgroup_mutex. Looking at the log, the culprit seems to be
> f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to
> RCU_LOCKDEP_WARN()"). It missed the bang for the second test while
> inverting it, so adding rcu_read_lock() isn't the right fix here.
>
> Paul, can you please fix it?
Gah! Please see below.
Thanx, Paul
------------------------------------------------------------------------
security/device_cgroup: Fix RCU_LOCKDEP_WARN() condition
f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()")
introduced a bug by incorrectly inverting the condition when moving from
rcu_lockdep_assert() to RCU_LOCKDEP_WARN(). This commit therefore fixes
the inversion.
Reported-by: Felipe Balbi <balbi@ti.com>
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Serge Hallyn <serge@hallyn.com>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 73455089feef..03c1652c9a1f 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -401,7 +401,7 @@ static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
bool match = false;
RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
- lockdep_is_held(&devcgroup_mutex),
+ !lockdep_is_held(&devcgroup_mutex),
"device_cgroup:verify_new_ex called without proper synchronization");
if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
next prev parent reply other threads:[~2015-09-03 0:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-31 20:40 [PATCH] security: device_cgroup: fix RCU lockdep splat Felipe Balbi
2015-09-01 9:12 ` Sebastian Ott
2015-09-01 13:08 ` Felipe Balbi
2015-09-02 12:29 ` Josh Boyer
2015-09-02 12:56 ` Felipe Balbi
2015-09-02 13:12 ` [PATCH v2] " Felipe Balbi
2015-09-02 15:27 ` Josh Boyer
2015-09-02 16:24 ` Tejun Heo
2015-09-03 0:14 ` Paul E. McKenney [this message]
2015-09-03 13:48 ` Serge E. Hallyn
2015-09-04 1:14 ` Paul E. McKenney
2015-09-03 13:56 ` Josh Boyer
2015-09-04 1:15 ` Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150903001433.GB4029@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=balbi@ti.com \
--cc=james.l.morris@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-omap@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=serge@hallyn.com \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).