linux-kernel - Re: 2.6.35-rc3-git8 - include/linux/fdtable.h:88 invoked rcu_dereference

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Date:	Mon, 9 Aug 2010 09:30:44 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Miles Lane <miles.lane@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.35-rc3-git8 - include/linux/fdtable.h:88 invoked
 rcu_dereference_check() without protection!

On Sun, Jul 04, 2010 at 06:04:20PM -0400, Miles Lane wrote:
> [ 1619.938226] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 1619.938230] ---------------------------------------------------
> [ 1619.938235] include/linux/fdtable.h:88 invoked
> rcu_dereference_check() without protection!
> [ 1619.938239]
> [ 1619.938240] other info that might help us debug this:
> [ 1619.938242]
> [ 1619.938245]
> [ 1619.938246] rcu_scheduler_active = 1, debug_locks = 1
> [ 1619.938250] no locks held by dbus-daemon/4254.
> [ 1619.938253]
> [ 1619.938254] stack backtrace:
> [ 1619.938260] Pid: 4254, comm: dbus-daemon Not tainted 2.6.35-rc3-git8 #5
> [ 1619.938264] Call Trace:
> [ 1619.938277]  [<ffffffff8106756a>] lockdep_rcu_dereference+0x9d/0xa6
> [ 1619.938286]  [<ffffffff810cae92>] fcheck_files+0xb1/0xca
> [ 1619.938292]  [<ffffffff810caf03>] fget_light+0x35/0x96
> [ 1619.938300]  [<ffffffff810d8d5e>] do_sys_poll+0x1ff/0x3e5
> [ 1619.938307]  [<ffffffff810d8572>] ? __pollwait+0x0/0xc7
> [ 1619.938314]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938320]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938327]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938333]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938340]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938346]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938353]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938359]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938365]  [<ffffffff810d8639>] ? pollwake+0x0/0x4f
> [ 1619.938374]  [<ffffffff810d90d8>] sys_poll+0x50/0xba
> [ 1619.938383]  [<ffffffff81009c82>] system_call_fastpath+0x16/0x1b

Hello, Miles!

Thank you again for your continued testing!

I believe that this one has been fixed by commit 844b9a8707f, which was
added in v2.6.35-rc6.  This commit added rcu_my_thread_group_empty()
to the list of rcu_dereference_check() conditions in the
rcu_dereference_check_fdtable() macro.

							Thanx, Paul
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