linux-kernel - cgroup.h:566 suspicious rcu_dereference

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Message-ID: <20121006131607.GA12798@localhost>
Date:	Sat, 6 Oct 2012 21:16:07 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: cgroup.h:566 suspicious rcu_dereference_check() usage!

Hi Aristeu,

I got the below warning in linus/master and linux-next, and it's
bisected down to:

commit ad676077a2ae4af4bb6627486ce19ccce04f1efe
Author: Aristeu Rozanski <aris@...hat.com>
Date:   Thu Oct 4 17:15:17 2012 -0700

    device_cgroup: convert device_cgroup internally to policy + exceptions


[    0.721405] 
[    0.721765] ===============================
[    0.722637] [ INFO: suspicious RCU usage. ]
[    0.723480] 3.6.0-03071-g283dbd8 #2 Not tainted
[    0.724562] -------------------------------
[    0.725481] /c/kernel-tests/src/tip/include/linux/cgroup.h:566 suspicious rcu_dereference_check() usage!
[    0.727399] 
[    0.727399] other info that might help us debug this:
[    0.727399] 
[    0.729131] 
[    0.729131] rcu_scheduler_active = 1, debug_locks = 1
[    0.730473] 2 locks held by swapper/0/1:
[    0.731337]  #0:  (sb_writers){.+.+.+}, at: [<ffffffff8112b5a3>] sb_start_write+0x1a/0x23
[    0.733062]  #1:  (&sb->s_type->i_mutex_key#2/1){+.+.+.}, at: [<ffffffff81118c0e>] kern_path_create+0xa1/0x1be
[    0.735330] 
[    0.735330] stack backtrace:
[    0.736199] Pid: 1, comm: swapper/0 Not tainted 3.6.0-03071-g283dbd8 #2
[    0.737618] Call Trace:
[    0.738187]  [<ffffffff81084896>] lockdep_rcu_suspicious+0x15a/0x16a
[    0.739489]  [<ffffffff8115c43f>] task_devcgroup+0xb9/0xcf
[    0.740645]  [<ffffffff8115cad5>] devcgroup_inode_mknod+0x21/0x8c
[    0.741926]  [<ffffffff81115a73>] vfs_mknod+0x98/0xf4
[    0.742635]  [<ffffffff81118d96>] ? user_path_create+0x6b/0x7d
[    0.743460]  [<ffffffff81119856>] sys_mknodat+0x17d/0x1db
[    0.744199]  [<ffffffff811198d3>] sys_mknod+0x1f/0x28
[    0.744931]  [<ffffffff815ebca8>] do_name+0x31a/0x37f
[    0.745603]  [<ffffffff815eac7e>] write_buffer+0x29/0x49
[    0.746312]  [<ffffffff815eb5e1>] unpack_to_rootfs+0x111/0x331
[    0.747091]  [<ffffffff815eb801>] ? unpack_to_rootfs+0x331/0x331
[    0.747938]  [<ffffffff815eb820>] populate_rootfs+0x1f/0x18d
[    0.748729]  [<ffffffff8100026c>] do_one_initcall+0xb6/0x1d2
[    0.749514]  [<ffffffff815ea2c6>] kernel_init+0x1de/0x2cf
[    0.750566]  [<ffffffff815e964e>] ? loglevel+0x46/0x46
[    0.751607]  [<ffffffff81298704>] kernel_thread_helper+0x4/0x10
[    0.752921]  [<ffffffff81296d74>] ? retint_restore_args+0x13/0x13
[    0.753838]  [<ffffffff815ea0e8>] ? start_kernel+0x651/0x651
[    0.754657]  [<ffffffff81298700>] ? gs_change+0x13/0x13
[    0.755558] Unpacking initramfs...
[    2.348617] Freeing initrd memory: 23656k freed

Thanks,
Fengguang

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