linux-kernel - suspicious rcu_dereference

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Message-ID: <20101107071414.GA3600@deepthought.bhanu.net>
Date:	Sun, 7 Nov 2010 15:14:14 +0800
From:	Arun Bhanu <ab@...nbhanu.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: suspicious rcu_dereference_check() usage splat

I got the following splat while booting 2.6.37-rc1+
(ff8b16d7e15a8ba2a6086645614a483e048e3fbf).

[    9.381536] ===================================================
[    9.382380] [ INFO: suspicious rcu_dereference_check() usage. ]
[    9.382867] ---------------------------------------------------
[    9.383412] kernel/pid.c:419 invoked rcu_dereference_check() without protection!
[    9.383959] 
[    9.383959] other info that might help us debug this:
[    9.383960] 
[    9.385599] 
[    9.385599] rcu_scheduler_active = 1, debug_locks = 0
[    9.386686] 1 lock held by readahead/365:
[    9.387227]  #0:  (tasklist_lock){.+.+..}, at: [<c05188f3>] sys_ioprio_set+0x84/0x261
[    9.387765] 
[    9.387765] stack backtrace:
[    9.388840] Pid: 365, comm: readahead Not tainted 2.6.37-rc1-ab1.fc14.i686.PAE+ #1
[    9.389374] Call Trace:
[    9.389909]  [<c07e57ba>] ? printk+0x25/0x2b
[    9.390453]  [<c046b21a>] lockdep_rcu_dereference+0x7d/0x86
[    9.390986]  [<c0459304>] find_task_by_pid_ns+0x3f/0x53
[    9.391521]  [<c0459335>] find_task_by_vpid+0x1d/0x1f
[    9.392050]  [<c051891b>] sys_ioprio_set+0xac/0x261
[    9.392574]  [<c046d80f>] ? trace_hardirqs_on_caller+0xfe/0x11f
[    9.393110]  [<c040951f>] sysenter_do_call+0x12/0x38

Complete dmesg and config attached. Let me know if you want me to test
any patches.

-Arun

View attachment "config" of type "text/plain" (101591 bytes)

View attachment "dmesg" of type "text/plain" (76266 bytes)