From: Zdenek Kabelac <zdenek.kabelac@gmail.com>
Subject: INFO: suspicious rcu_dereference_check()
Date: Thu, 25 Mar 2010 11:48:49 +0100
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Hi

I've enabled rcu correctness for my  todays 2.6.34-rc2 kernel.

I'm getting this INFO: from my kvm guest (which uses host's nfs
exported directory.)
This

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
fs/nfs/delegation.c:348 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
2 locks held by rm/1820:
 #0:  (&sb->s_type->i_mutex_key#13/1){+.+.+.}, at:
[<ffffffff81138e1b>] do_unlinkat+0x9b/0x1c0
 #1:  (&sb->s_type->i_mutex_key#13){+.+.+.}, at: [<ffffffff81136a76>]
vfs_unlink+0x56/0xf0

stack backtrace:
Pid: 1820, comm: rm Not tainted 2.6.34-rc2-00186-ge79a302 #60
Call Trace:
 [<ffffffff810819fb>] lockdep_rcu_dereference+0xbb/0xc0
 [<ffffffffa0228351>] nfs_inode_return_delegation+0x101/0x110 [nfs]
 [<ffffffffa01fd58d>] nfs_unlink+0xad/0x2a0 [nfs]
 [<ffffffff81136aba>] vfs_unlink+0x9a/0xf0
 [<ffffffff81148365>] ? mnt_want_write+0x65/0xb0
 [<ffffffff81138f03>] do_unlinkat+0x183/0x1c0
 [<ffffffff8142b66d>] ? retint_swapgs+0xe/0x13
 [<ffffffff81083985>] ? trace_hardirqs_on_caller+0x155/0x1a0
 [<ffffffff8142a232>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff811390a2>] sys_unlinkat+0x22/0x40
 [<ffffffff81031dc8>] sysenter_dispatch+0x7/0x2c


Zdenek