linux-kernel - Re: suspicious RCU usage in cgroup

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Date:	Wed, 17 Oct 2012 12:26:23 -0400
From:	Dave Jones <davej@...hat.com>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: suspicious RCU usage in cgroup

On Fri, Oct 05, 2012 at 06:06:12PM -0400, Aristeu Rozanski wrote:
 > Hi Dave,
 > On Fri, Oct 05, 2012 at 05:59:29PM -0400, Dave Jones wrote:
 > > On boot in Linus' current tree..
 > > 
 > > ===============================
 > > [ INFO: suspicious RCU usage. ]
 > > 3.6.0+ #22 Not tainted
 > > -------------------------------
 > > include/linux/cgroup.h:566 suspicious rcu_dereference_check() usage!
 > > 
 > > other info that might help us debug this:
 > > 
 > > rcu_scheduler_active = 1, debug_locks = 1
 > > 2 locks on stack by kdevtmpfs/59:
 > >  #0: blocked:  (sb_writers){.+.+.+}, instance: ffff88014595a9a0, at: [<ffffffff81207bc4>] mnt_want_write+0x24/0x50
 > >  #1: held:     (&sb->s_type->i_mutex_key#3/1){+.+.+.}, instance: ffff880145b1f5c8, at: [<ffffffff811f26d4>] kern_path_create+0x84/0x170
 > > 
 > > stack backtrace:
 > > Pid: 59, comm: kdevtmpfs Not tainted 3.6.0+ #22
 > > Call Trace:
 > >  [<ffffffff810df1f2>] lockdep_rcu_suspicious+0xe2/0x130
 > >  [<ffffffff81317cad>] devcgroup_inode_mknod+0x19d/0x240
 > >  [<ffffffff812f54d8>] ? security_capable+0x18/0x20
 > >  [<ffffffff8107e214>] ? ns_capable+0x44/0x80
 > >  [<ffffffff811f3b0e>] vfs_mknod+0x7e/0x140
 > >  [<ffffffff81452967>] handle_create.isra.2+0x77/0x210
 > >  [<ffffffff810ddd6c>] ? lock_release_holdtime.part.26+0xcc/0x140
 > >  [<ffffffff810afbf1>] ? get_parent_ip+0x11/0x50
 > >  [<ffffffff816bacd9>] ? sub_preempt_count+0x79/0xd0
 > >  [<ffffffff81452c47>] devtmpfsd+0x147/0x170
 > >  [<ffffffff81452b00>] ? handle_create.isra.2+0x210/0x210
 > >  [<ffffffff8109bf8d>] kthread+0xed/0x100
 > >  [<ffffffff816bacd9>] ? sub_preempt_count+0x79/0xd0
 > >  [<ffffffff816c04a4>] kernel_thread_helper+0x4/0x10
 > >  [<ffffffff810a9fdc>] ? finish_task_switch+0x7c/0x120
 > >  [<ffffffff816b62db>] ? _raw_spin_unlock_irq+0x4b/0x80
 > >  [<ffffffff816b6d37>] ? retint_restore_args+0x13/0x13
 > >  [<ffffffff8109bea0>] ? kthread_create_on_node+0x160/0x160
 > >  [<ffffffff816c04a0>] ? gs_change+0x13/0x13
 > 
 > "[PATCH] cgroup: fix invalid rcu dereference" which is being routed thru
 > akpm's tree should fix this.
 > 
 > see https://patchwork.kernel.org/patch/1456571/

What's happening with this ?

	Dave

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