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 14:04:46 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Richard Guy Briggs <rgb@...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 Thu, 2014-12-18 at 13:44 -0500, Richard Guy Briggs wrote:
> 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.

I'd suggest just sending the GFP type, not the who audit_buffer, but
that's up to you.

-Eric

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