linux-kernel - 2.6.35+vfs-scale: INFO: suspicious rcu_dereference

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Message-ID: <AANLkTiniV_jqMi4vN5yw7q-NjsH1WAPgauWqwy9uxO-A@mail.gmail.com>
Date:	Mon, 16 Aug 2010 18:57:36 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Howells <dhowells@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() usage (kernel/exit.c:1387)

Hi,

I was testing your VFS scaling tree*, but I get the following in my dmesg:

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/exit.c:1387 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 1
2 locks held by bash/2878:
 #0:  (tasklist_lock){.+.+..}, at: [<ffffffff8103a275>] do_wait+0xb3/0x200
 #1:  (&(&sighand->siglock)->rlock){-.....}, at: [<ffffffff810399e9>]
wait_consider_task+0x2ca/0xaa3

stack backtrace:
Pid: 2878, comm: bash Not tainted 2.6.35-00079-g4067b85 #7
Call Trace:
 [<ffffffff8105e9f2>] lockdep_rcu_dereference+0x9b/0xa6
 [<ffffffff8103a036>] wait_consider_task+0x917/0xaa3
 [<ffffffff8102cf36>] ? add_preempt_count+0xc2/0xc9
 [<ffffffff8103a29d>] do_wait+0xdb/0x200
 [<ffffffff8103a45b>] sys_wait4+0x99/0xd3
 [<ffffffff810387e5>] ? child_wait_callback+0x0/0x5d
 [<ffffffff8109be66>] ? might_fault+0x96/0xbc
 [<ffffffff810737a6>] compat_sys_wait4+0x8a/0xc1
 [<ffffffff8109be83>] ? might_fault+0xb3/0xbc
 [<ffffffff8109be38>] ? might_fault+0x68/0xbc
 [<ffffffff815d02c3>] ? trace_hardirqs_off_thunk+0x3a/0x3c
 [<ffffffff8102862c>] sys32_waitpid+0xb/0xd
 [<ffffffff81027bb4>] sysenter_dispatch+0x7/0x30
 [<ffffffff815d0284>] ? trace_hardirqs_on_thunk+0x3a/0x3f

I don't think it's related to the VFS patches, however, so I added
some other (maybe relevant) CCs too.

At the time I was simply invoking gcc from bash.


Vegard

* git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin.git
branch vfs-scale
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