linux-kernel - Re: linux-next 20141216 BUG: sleeping function called from invalid context at mm/slab.c:2849

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Date:	Thu, 18 Dec 2014 13:44:20 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-audit@...hat.com, selinux@...ho.nsa.gov,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next 20141216 BUG: sleeping function called from invalid
 context at mm/slab.c:2849

On 14/12/18, Eric Paris wrote:
> On Thu, 2014-12-18 at 12:46 -0500, Richard Guy Briggs wrote:
> > On 14/12/18, Eric Paris wrote:
> > > On Thu, 2014-12-18 at 11:45 -0500, Valdis.Kletnieks@...edu wrote:
> > > > On Tue, 16 Dec 2014 20:09:54 -0500, Valdis Kletnieks said:
> > > > > Spotted these two while booting single-user on 20141216.  20141208
> > > > > doesn't throw these, so it's something in the last week or so..
> > > > 
> > > > Gaah!  Turns out that 20141208 *is* susceptible - it had been booting
> > > > just fine for several days, but it went around the bend, apparently due
> > > > to a userspace or initrd change.
> > > 
> > > $5 says you updated systemd?
> > > 
> > > Richard?
> > 
> > Ok, so if you are correct, then either we justify dropping the lock (I
> > assume the one commone to both BUG reports [sig->cred_guard_mutex] ),
> > or we make yet another queue were were hoping to avoid...
> > 
> > It would also be good to narrow it down to a rule that triggers this.
> 
> I thought the first message was enough to find the problem, but:
> 
> static void kauditd_send_multicast_skb(struct sk_buff *skb)
> {
> ...
>         nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, GFP_KERNEL);
> ...
> }
> 
> Since kauditd_send_multicast_skb() gets called in audit_log_end(), which
> can come from any context (aka even a sleeping context) you can't use
> GFP_KERNEL.  The audit_buffer know what context it should use.  So pass
> that down and use that.

Ok, that looks more obvious now...  We just need to change the internal
interface to kauditd_send_multicast_skb() to accept an audit_buffer
instead of just the skb and use the gfp_mask value from there instead of
using our own...

Thanks, Eric.

> -Eric
> 
> > > > egrep 'BUG|Linux vers' from my syslog:
> > > > 
> > > > Dec  9 12:19:53 turing-police kernel: [    0.000000] Linux version 3.18.0-next-20141208 (source@...ing-police.cc.vt.edu) (gcc version 4.9.2 20141101 (Red Hat 4.9.2-1) (GCC) ) #27 SMP PREEMPT Mon Dec 8 22:20:07 EST 2014
> > ...
> > > > Dec 12 19:42:30 turing-police kernel: [    0.000000] Linux version 3.18.0-next-20141208 (source@...ing-police.cc.vt.edu) (gcc version 4.9.2 20141101 (Red Hat 4.9.2-1) (GCC) ) #27 SMP PREEMPT Mon Dec 8 22:20:07 EST 2014
> > > > Dec 12 20:00:39 turing-police kernel: [ 1109.635328] BUG: sleeping function called from invalid context at mm/slab.c:2849
> > ...
> > > > Dec 12 20:42:47 turing-police kernel: [ 3633.863552] BUG: sleeping function called from invalid context at mm/slab.c:2849
> > > > Dec 12 20:51:33 turing-police kernel: [    0.000000] Linux version 3.18.0-next-20141208 (source@...ing-police.cc.vt.edu) (gcc version 4.9.2 20141101 (Red Hat 4.9.2-1) (GCC) ) #27 SMP PREEMPT Mon Dec 8 22:20:07 EST 2014
> > > > Dec 12 21:51:04 turing-police kernel: [ 3587.132867] BUG: sleeping function called from invalid context at mm/slab.c:2849
> > ...
> > > > I need to figure out what changed around 7:30PM on the 12th.
> > 
> > - RGB

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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