Re: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() usage (kernel/exit.c:1387)

[Vegard Nossum]

Nick Piggin might update his git config because the commits in the
vfs-scale tree appear to bear an invalid e-mail address. Please reply
to this e-mail instead. Thanks.

Vegard


---------- Forwarded message ----------
From: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Date: 16 August 2010 18:57
Subject: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check()
usage (kernel/exit.c:1387)
To: Nick Piggin <npiggin@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>, David Howells
<dhowells@xxxxxxxxxx>, "Paul E. McKenney"
<paulmck@xxxxxxxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>


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:
Â#0: Â(tasklist_lock){.+.+..}, at: [<ffffffff8103a275>] do_wait+0xb3/0x200
Â#1: Â(&(&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:
Â[<ffffffff8105e9f2>] lockdep_rcu_dereference+0x9b/0xa6
Â[<ffffffff8103a036>] wait_consider_task+0x917/0xaa3
Â[<ffffffff8102cf36>] ? add_preempt_count+0xc2/0xc9
Â[<ffffffff8103a29d>] do_wait+0xdb/0x200
Â[<ffffffff8103a45b>] sys_wait4+0x99/0xd3
Â[<ffffffff810387e5>] ? child_wait_callback+0x0/0x5d
Â[<ffffffff8109be66>] ? might_fault+0x96/0xbc
Â[<ffffffff810737a6>] compat_sys_wait4+0x8a/0xc1
Â[<ffffffff8109be83>] ? might_fault+0xb3/0xbc
Â[<ffffffff8109be38>] ? might_fault+0x68/0xbc
Â[<ffffffff815d02c3>] ? trace_hardirqs_off_thunk+0x3a/0x3c
Â[<ffffffff8102862c>] sys32_waitpid+0xb/0xd
Â[<ffffffff81027bb4>] sysenter_dispatch+0x7/0x30
Â[<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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