| Message ID | 1441199548-29633-1-git-send-email-balbi@ti.com |
|---|---|
| State | New |
| Headers | show |
On Wed, Sep 2, 2015 at 9:12 AM, Felipe Balbi <balbi@ti.com> 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! > [ 12.033576] other info that might help us debug this: > > [ 12.041942] rcu_scheduler_active = 1, debug_locks = 0 > [ 12.048796] 4 locks held by systemd/1: > [ 12.052700] #0: (sb_writers#7){.+.+.+}, at: [<c017af84>] __sb_start_write+0x8c/0xb0 > [ 12.060954] #1: (&of->mutex){+.+.+.}, at: [<c01f1600>] kernfs_fop_write+0x50/0x1b8 > [ 12.069085] #2: (s_active#30){++++.+}, at: [<c01f1608>] kernfs_fop_write+0x58/0x1b8 > [ 12.077310] #3: (devcgroup_mutex){+.+...}, at: [<c0317bfc>] devcgroup_access_write+0x20/0x658 > [ 12.086575] stack backtrace: > [ 12.091124] CPU: 0 PID: 1 Comm: systemd Not tainted 4.2.0-next-20150831 #1154 > [ 12.098609] Hardware name: Generic AM43 (Flattened Device Tree) > [ 12.104807] [<c001770c>] (unwind_backtrace) from [<c0013a58>] (show_stack+0x10/0x14) > [ 12.112924] [<c0013a58>] (show_stack) from [<c034f014>] (dump_stack+0x84/0x9c) > [ 12.120491] [<c034f014>] (dump_stack) from [<c0317a04>] (verify_new_ex+0xc4/0xdc) > [ 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) > > Fix it by making sure rcu_read_lock() is held > around calls to parent_has_perm(). > > Signed-off-by: Felipe Balbi <balbi@ti.com> This cleared up the splat on all my machines and I don't see any other side effects (even with lockdep enabled). Thanks! Tested-by: Josh Boyer <jwboyer@fedoraproject.org> josh > --- > > Changes since v1: > - move rcu_read_lock/unlock to wrap parent_has_perm() > > security/device_cgroup.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/security/device_cgroup.c b/security/device_cgroup.c > index 73455089feef..dd77ed206fa4 100644 > --- a/security/device_cgroup.c > +++ b/security/device_cgroup.c > @@ -608,6 +608,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, > int count, rc = 0; > struct dev_exception_item ex; > struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent); > + int ret; > > if (!capable(CAP_SYS_ADMIN)) > return -EPERM; > @@ -734,7 +735,11 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, > break; > } > > - if (!parent_has_perm(devcgroup, &ex)) > + rcu_read_lock(); > + ret = parent_has_perm(devcgroup, &ex); > + rcu_read_unlock(); > + > + if (!ret) > return -EPERM; > rc = dev_exception_add(devcgroup, &ex); > break; > -- > 2.5.0 > > -- > 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/ -- 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/
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? Thanks.
On Wed, Sep 02, 2015 at 05:14:33PM -0700, 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] [<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> Oh, makes sense :) (didn't see the original patch when it came by, sorry) Acked-by: Serge Hallyn <serge.hallyn@canonical.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) { -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Sep 2, 2015 at 8:14 PM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> 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] [<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> Just tested this patch without Felipe's previous version on all my machines. The splat is indeed gone. Tested-by: Josh Boyer <jwboyer@fedoraproject.org> 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/ -- 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/
On Thu, Sep 03, 2015 at 08:48:39AM -0500, Serge E. Hallyn wrote: > On Wed, Sep 02, 2015 at 05:14:33PM -0700, 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] [<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> > > Oh, makes sense :) (didn't see the original patch when it came by, sorry) I should have CCed you, apologies for failing to do so. > Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Added, thank you! Thanx, Paul > > 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/
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 > <paulmck@linux.vnet.ibm.com> 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] [<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> > > Just tested this patch without Felipe's previous version on all my > machines. The splat is indeed gone. > > Tested-by: Josh Boyer <jwboyer@fedoraproject.org> 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/ > -- 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/
diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 73455089feef..dd77ed206fa4 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c @@ -608,6 +608,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, int count, rc = 0; struct dev_exception_item ex; struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent); + int ret; if (!capable(CAP_SYS_ADMIN)) return -EPERM; @@ -734,7 +735,11 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, break; } - if (!parent_has_perm(devcgroup, &ex)) + rcu_read_lock(); + ret = parent_has_perm(devcgroup, &ex); + rcu_read_unlock(); + + if (!ret) return -EPERM; rc = dev_exception_add(devcgroup, &ex); break;
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! [ 12.033576] other info that might help us debug this: [ 12.041942] rcu_scheduler_active = 1, debug_locks = 0 [ 12.048796] 4 locks held by systemd/1: [ 12.052700] #0: (sb_writers#7){.+.+.+}, at: [<c017af84>] __sb_start_write+0x8c/0xb0 [ 12.060954] #1: (&of->mutex){+.+.+.}, at: [<c01f1600>] kernfs_fop_write+0x50/0x1b8 [ 12.069085] #2: (s_active#30){++++.+}, at: [<c01f1608>] kernfs_fop_write+0x58/0x1b8 [ 12.077310] #3: (devcgroup_mutex){+.+...}, at: [<c0317bfc>] devcgroup_access_write+0x20/0x658 [ 12.086575] stack backtrace: [ 12.091124] CPU: 0 PID: 1 Comm: systemd Not tainted 4.2.0-next-20150831 #1154 [ 12.098609] Hardware name: Generic AM43 (Flattened Device Tree) [ 12.104807] [<c001770c>] (unwind_backtrace) from [<c0013a58>] (show_stack+0x10/0x14) [ 12.112924] [<c0013a58>] (show_stack) from [<c034f014>] (dump_stack+0x84/0x9c) [ 12.120491] [<c034f014>] (dump_stack) from [<c0317a04>] (verify_new_ex+0xc4/0xdc) [ 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) Fix it by making sure rcu_read_lock() is held around calls to parent_has_perm(). Signed-off-by: Felipe Balbi <balbi@ti.com> --- Changes since v1: - move rcu_read_lock/unlock to wrap parent_has_perm() security/device_cgroup.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)