Re: [PATCH] conditionally reschedule while loading selinux policy.

From: Dave Jones
Date: Thu Oct 03 2013 - 16:40:50 EST


On Thu, Oct 03, 2013 at 04:36:10PM -0400, Paul Moore wrote:
> On Monday, September 30, 2013 05:13:42 PM Dave Jones wrote:
> > On Mon, Sep 30, 2013 at 01:37:53PM -0400, Stephen Smalley wrote:
> > > > With that patch applied, the problem seems to have moved elsewhere..
> > >
> > > Sorry, what locks are we holding there? You ought to be able to do a
> > > cond_resched() anywhere during policydb_read() AFAIK; it is loading the
> > > policy into a new structure that isn't being accessed by anything else
> > > yet and the policy_rwlock is only held by security_load_policy after
> > > calling policydb_read and only to switch it into place as the active
> > > policydb.
> >
> > Hmm, I thought I had tried this already, and got a lot of spew, but it turns
> > out for some reason I had previously patched hashtab_search instead.
> >
> > I'll try running with this for a while..
>
> Hi Dave,
>
> Just checking to see if this patch solved your problem ... ?
>
> > diff --git a/security/selinux/ss/hashtab.c b/security/selinux/ss/hashtab.c
> > index 933e735..2cc4961 100644
> > --- a/security/selinux/ss/hashtab.c
> > +++ b/security/selinux/ss/hashtab.c
> > @@ -6,6 +6,7 @@
> > #include <linux/kernel.h>
> > #include <linux/slab.h>
> > #include <linux/errno.h>
> > +#include <linux/sched.h>
> > #include "hashtab.h"
> >
> > struct hashtab *hashtab_create(u32 (*hash_value)(struct hashtab *h, const
> > void *key), @@ -40,6 +41,8 @@ int hashtab_insert(struct hashtab *h, void
> > *key, void *datum) u32 hvalue;
> > struct hashtab_node *prev, *cur, *newnode;
> >
> > + cond_resched();
> > +
> > if (!h || h->nel == HASHTAB_MAX_NODES)
> > return -EINVAL;

I couldn't get a backtrace when I downgraded, and reupgraded my policy,
but that said, I didn't when I tested that way on my first patch either.
It wasn't until I got a newer policy that I saw the 2nd spew.
I was planning on sitting on this until the next policy update just
to confirm.

Dave

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