From 85f4e5ec7bbb5f8d7cc023a12af39d76c05cd204 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Wed, 2 Sep 2015 17:14:33 -0700
Subject: [PATCH] security: device_cgroup: fix RCU lockdep splat
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>
---
security/device_cgroup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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) {
--
2.4.3