Messages in this thread | | | Date | Mon, 14 Jan 2013 21:47:10 -0500 | From | Sasha Levin <> | Subject | cpuset: lockdep spew on proc_cpuset_show |
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Hi Tejun,
I've stumbled on the following:
[ 75.972016] =============================== [ 75.977317] [ INFO: suspicious RCU usage. ] [ 76.041031] 3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 Tainted: G W [ 76.057535] ------------------------------- [ 76.063397] include/linux/cgroup.h:534 suspicious rcu_dereference_check() usage! [ 76.076333] [ 76.076333] other info that might help us debug this: [ 76.076333] [ 76.087091] [ 76.087091] rcu_scheduler_active = 1, debug_locks = 1 [ 76.098682] 2 locks held by trinity/7514: [ 76.104154] #0: (&p->lock){+.+.+.}, at: [<ffffffff812b06aa>] seq_read+0x3a/0x3e0 [ 76.119533] #1: (cpuset_mutex){+.+...}, at: [<ffffffff811abae4>] proc_cpuset_show+0x84/0x190 [ 76.151167] [ 76.151167] stack backtrace: [ 76.156853] Pid: 7514, comm: trinity Tainted: G W 3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 [ 76.180547] Call Trace: [ 76.183754] [<ffffffff81182cab>] lockdep_rcu_suspicious+0x10b/0x120 [ 76.191885] [<ffffffff811abb71>] proc_cpuset_show+0x111/0x190 [ 76.200572] [<ffffffff812b0827>] seq_read+0x1b7/0x3e0 [ 76.206843] [<ffffffff812b0670>] ? seq_lseek+0x110/0x110 [ 76.213562] [<ffffffff8128b4fb>] do_loop_readv_writev+0x4b/0x90 [ 76.220961] [<ffffffff8128b776>] do_readv_writev+0xf6/0x1d0 [ 76.227940] [<ffffffff8128b8ee>] vfs_readv+0x3e/0x60 [ 76.235971] [<ffffffff8128b960>] sys_readv+0x50/0xd0 [ 76.241945] [<ffffffff83d33d18>] tracesys+0xe1/0xe6
This is the result of "cpuset: replace cgroup_mutex locking with cpuset internal locking" which remove the cgroup_lock() before calling task_subsys_state(), which now complains since one of the debug conditions in the rcu_dereference_check() there is cgroup_lock_is_held().
I'm not sure if this is an actual issue, but I do see that task_subsys_state() gets called from other places as well, so I think that possibly lockdep is right here and we do need to fix up locking there, but again, I'm not sure...
Thanks, Sasha
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