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

From: Paul Moore
Date: Thu Oct 03 2013 - 16:36:20 EST


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..
> > >
> > > BUG: soft lockup - CPU#3 stuck for 22s! [load_policy:8119]
> > >
> > > irq event stamp: 1590886
> > > hardirqs last enabled at (1590885): [<ffffffff8152c3dd>]
> > > __slab_alloc.constprop.78+0x4c0/0x4d7 hardirqs last disabled at
> > > (1590886): [<ffffffff8153e06a>] apic_timer_interrupt+0x6a/0x80
> > > softirqs last enabled at (1590336): [<ffffffff810480d9>]
> > > __do_softirq+0x169/0x200 softirqs last disabled at (1590331):
> > > [<ffffffff8104839d>] irq_exit+0x11d/0x140 RIP:
> > > 0010:[<ffffffff81223182>] [<ffffffff81223182>]
> > > hashtab_insert+0x62/0x110 > >
> > > Call Trace:
> > > [<ffffffff812283b5>] policydb_read+0xc25/0x1200
> >
> > ...
> >
> > > We're holding a bunch of locks here, so we can't just cond_resched.
> > > Thoughts ?
> >
> > 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;

--
paul moore
www.paul-moore.com

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