From 85f4e5ec7bbb5f8d7cc023a12af39d76c05cd204 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" 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] [] (verify_new_ex) from [] (devcgroup_access_write+0x374/0x658) > > [ 12.137426] [] (devcgroup_access_write) from [] (cgroup_file_write+0x28/0x1bc) > > [ 12.146796] [] (cgroup_file_write) from [] (kernfs_fop_write+0xc0/0x1b8) > > [ 12.155620] [] (kernfs_fop_write) from [] (__vfs_write+0x1c/0xd8) > > [ 12.163783] [] (__vfs_write) from [] (vfs_write+0x90/0x16c) > > [ 12.171426] [] (vfs_write) from [] (SyS_write+0x44/0x9c) > > [ 12.178806] [] (SyS_write) from [] (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 Reported-by: Tejun Heo Signed-off-by: Paul E. McKenney Cc: Serge Hallyn --- 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