Security/cgroup suspicious RCU usage with v4.2-2744-g65a99597f044

[Josh Boyer]

Hi All,

All of my test machines hit the backtrace below with Linus' tree as of
this morning.  Any ideas?

josh


[  +0.160966] ===============================
[  +0.000001] [ INFO: suspicious RCU usage. ]
[  +0.000002] 4.3.0-0.rc0.git1.1.fc24.x86_64 #1 Not tainted
[  +0.000001] -------------------------------
[  +0.000002] security/device_cgroup.c:405 device_cgroup:verify_new_ex
called without proper synchronization!
[  +0.000000]
              other info that might help us debug this:

[  +0.000001]
              rcu_scheduler_active = 1, debug_locks = 0
[  +0.000002] 4 locks held by systemd/1:
[  +0.000010]  #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff81267f87>]
vfs_write+0x187/0x1a0
[  +0.000006]  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff812f3996>]
kernfs_fop_write+0x66/0x190
[  +0.000005]  #2:  (s_active#61){++++.+}, at: [<ffffffff812f399e>]
kernfs_fop_write+0x6e/0x190
[  +0.000007]  #3:  (devcgroup_mutex){+.+...}, at:
[<ffffffff813ada3c>] devcgroup_access_write+0x3c/0x6e0
[  +0.000000]
              stack backtrace:
[  +0.000003] CPU: 3 PID: 1 Comm: systemd Not tainted
4.3.0-0.rc0.git1.1.fc24.x86_64 #1
[  +0.000001] Hardware name:                  /D34010WYK, BIOS
WYLPT10H.86A.0026.2014.0514.1714 05/14/2014
[  +0.000004]  0000000000000000 000000006dc9945a ffff88040ce73c68
ffffffff8184e49c
[  +0.000003]  0000000000000000 ffff88040cdd4000 ffff88040ce73c98
ffffffff81101437
[  +0.000003]  ffff880408646d00 ffff88040ce73d00 0000000000000002
0000000000000001
[  +0.000001] Call Trace:
[  +0.000006]  [<ffffffff8184e49c>] dump_stack+0x4c/0x65
[  +0.000004]  [<ffffffff81101437>] lockdep_rcu_suspicious+0xd7/0x110
[  +0.000004]  [<ffffffff813ad6e8>] verify_new_ex+0xd8/0xe0
[  +0.000003]  [<ffffffff813addaf>] devcgroup_access_write+0x3af/0x6e0
[  +0.000005]  [<ffffffff81023999>] ? sched_clock+0x9/0x10
[  +0.000004]  [<ffffffff811599e4>] cgroup_file_write+0x44/0x1e0
[  +0.000003]  [<ffffffff812f3a71>] kernfs_fop_write+0x141/0x190
[  +0.000002]  [<ffffffff81267497>] __vfs_write+0x37/0x100
[  +0.000002]  [<ffffffff81267f87>] ? vfs_write+0x187/0x1a0
[  +0.000004]  [<ffffffff8138929d>] ? security_file_permission+0x3d/0xc0
[  +0.000002]  [<ffffffff81267ea9>] vfs_write+0xa9/0x1a0
[  +0.000003]  [<ffffffff81268bc8>] SyS_write+0x58/0xd0
[  +0.000004]  [<ffffffff818580ee>] entry_SYSCALL_64_fastpath+0x12/0x76
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