From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v2] security: device_cgroup: fix RCU lockdep splat Date: Thu, 3 Sep 2015 18:15:11 -0700 Message-ID: <20150904011511.GU4029@linux.vnet.ibm.com> References: <20150902125608.GA8299@saruman.tx.rr.com> <1441199548-29633-1-git-send-email-balbi@ti.com> <20150902162450.GJ22326@mtj.duckdns.org> <20150903001433.GB4029@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Josh Boyer Cc: Tejun Heo , Felipe Balbi , James Morris , "Serge E. Hallyn" , linux-security-module , "Linux-Kernel@Vger. Kernel. Org" , Linux OMAP Mailing List List-Id: linux-omap@vger.kernel.org On Thu, Sep 03, 2015 at 09:56:05AM -0400, Josh Boyer wrote: > On Wed, Sep 2, 2015 at 8:14 PM, Paul E. McKenney > wrote: > > 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 > > Just tested this patch without Felipe's previous version on all my > machines. The splat is indeed gone. > > Tested-by: Josh Boyer Thank you, added! Thanx, Paul > josh > > > > > 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) { > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ >