On 2013/1/15 10:47, Sasha Levin wrote:
> 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...
>
I've prepared a fix.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
