linux-kernel - Re: [ipc,shm] BUG: lock held when returning to user space!

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Message-ID: <1375416169.2269.3.camel@buesod1.americas.hpqcorp.net>
Date:	Thu, 01 Aug 2013 21:02:49 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>,
	Xiaotian Feng <xtfeng@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [ipc,shm] BUG: lock held when returning to user space!

On Sat, 2013-07-27 at 21:34 +0800, Fengguang Wu wrote:
> On Sat, Jul 20, 2013 at 09:46:45AM -0700, Davidlohr Bueso wrote:
> > On Sun, 2013-07-21 at 00:02 +0800, Xiaotian Feng wrote:
> > > On Sat, Jul 20, 2013 at 9:13 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> > > > Greetings,
> > > >
> > > > I got the below dmesg and the first bad commit is
> > > >
> > > > commit c5d0282a0405b0a81fa3390e4230e4cbb3ced7a2
> > > > Author: Davidlohr Bueso <davidlohr.bueso@...com>
> > > > Date:   Fri Jul 19 09:56:58 2013 +1000
> > > >
> > > >     ipc,shm: shorten critical region for shmat
> > > >
> > > >     Similar to other system calls, acquire the kern_ipc_perm lock after doing
> > > >     the initial permission and security checks.
> > > >
> > > >     Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
> > > >     Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> > > >     Cc: Rik van Riel <riel@...hat.com>
> > > >     Cc: Manfred Spraul <manfred@...orfullife.com>
> > > >     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > > >
> > > > [   20.702156]
> > > > [   20.702493] ================================================
> > > > [   20.703511] [ BUG: lock held when returning to user space! ]
> > > > [   20.704532] 3.11.0-rc1-next-20130719 #50 Not tainted
> > > > [   20.705416] ------------------------------------------------
> > > > [   20.706425] trinity-child0/174 is leaving the kernel with locks still held!
> > > > [   20.707638] 1 lock held by trinity-child0/174:
> > > > [   20.708475]  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff814a8491>] do_shmat+0xe1/0x500
> > > >
> > > 
> > > ----
> > > ns = current->nsproxy->ipc_ns;
> > > - shp = shm_lock_check(ns, shmid);
> > > + rcu_read_lock();
> > > + shp = shm_obtain_object_check(ns, shmid);
> > > if (IS_ERR(shp)) {
> > > err = PTR_ERR(shp);
> > > goto out;
> > > ----
> > > 
> > > If shm_obtain_object_check() failed, goto out will return with
> > > rcu_read_lock() held.  I think following patch should cure this.
> > 
> > Yep that should solve it, sorry about that. Sasha Levin sent out a fix
> > for it yesterday (offline).
> 
> What's the patch's status? The bug is still there in linux-next 20130726.

Andrew, unless you have an objection (or have already done so), could
you pickup Sasha's fix?

Thanks,
Davidlohr

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