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

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Date:	Mon, 30 Sep 2013 17:13:42 -0400
From:	Dave Jones <davej@...hat.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>, eparis@...hat.com,
	james.l.morris@...cle.com, Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH] conditionally reschedule while loading selinux policy.

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..

	Dave


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;
 
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