linux-kernel - Re: [1/2] conditionally reschedule in mls_convert

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Date:	Thu, 15 May 2014 15:18:07 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, pmoore@...hat.com,
	eparis@...hat.com
Subject: Re: [1/2] conditionally reschedule in mls_convert_context while loading
 selinux policy.

On 05/15/2014 03:02 PM, Dave Jones wrote:
> On a slow machine (with debugging enabled), upgrading selinux policy may take
> a considerable amount of time. Long enough that the softlockup detector
> gets triggered.
> 
> The backtrace looks like this..
> 
>  > BUG: soft lockup - CPU#2 stuck for 23s! [load_policy:19045]
>  > Call Trace:
>  >  [<ffffffff81221ddf>] symcmp+0xf/0x20
>  >  [<ffffffff81221c27>] hashtab_search+0x47/0x80
>  >  [<ffffffff8122e96c>] mls_convert_context+0xdc/0x1c0
>  >  [<ffffffff812294e8>] convert_context+0x378/0x460
>  >  [<ffffffff81229170>] ? security_context_to_sid_core+0x240/0x240
>  >  [<ffffffff812221b5>] sidtab_map+0x45/0x80
>  >  [<ffffffff8122bb9f>] security_load_policy+0x3ff/0x580
>  >  [<ffffffff810788a8>] ? sched_clock_cpu+0xa8/0x100
>  >  [<ffffffff810786dd>] ? sched_clock_local+0x1d/0x80
>  >  [<ffffffff810788a8>] ? sched_clock_cpu+0xa8/0x100
>  >  [<ffffffff8103096a>] ? __change_page_attr_set_clr+0x82a/0xa50
>  >  [<ffffffff810786dd>] ? sched_clock_local+0x1d/0x80
>  >  [<ffffffff810788a8>] ? sched_clock_cpu+0xa8/0x100
>  >  [<ffffffff8103096a>] ? __change_page_attr_set_clr+0x82a/0xa50
>  >  [<ffffffff810788a8>] ? sched_clock_cpu+0xa8/0x100
>  >  [<ffffffff81534ddc>] ? retint_restore_args+0xe/0xe
>  >  [<ffffffff8109c82d>] ? trace_hardirqs_on_caller+0xfd/0x1c0
>  >  [<ffffffff81279a2e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>  >  [<ffffffff810d28a8>] ? rcu_irq_exit+0x68/0xb0
>  >  [<ffffffff81534ddc>] ? retint_restore_args+0xe/0xe
>  >  [<ffffffff8121e947>] sel_write_load+0xa7/0x770
>  >  [<ffffffff81139633>] ? vfs_write+0x1c3/0x200
>  >  [<ffffffff81210e8e>] ? security_file_permission+0x1e/0xa0
>  >  [<ffffffff8113952b>] vfs_write+0xbb/0x200
>  >  [<ffffffff811581c7>] ? fget_light+0x397/0x4b0
>  >  [<ffffffff81139c27>] SyS_write+0x47/0xa0
>  >  [<ffffffff8153bde4>] tracesys+0xdd/0xe2
> 
> Stephen Smalley suggested:
> 
>  > Maybe put a cond_resched() within the ebitmap_for_each_positive_bit()
>  > loop in mls_convert_context()?
> 
> That seems to do the trick. Tested by downgrading and re-upgrading selinux-policy-targeted.
> 
> Signed-off-by: Dave Jones <davej@...hat.com>

Acked-by:  Stephen Smalley <sds@...ho.nsa.gov>

> 
> ---
>  security/selinux/ss/mls.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
> index c85bc1ec040c..d307b37ddc2b 100644
> --- a/security/selinux/ss/mls.c
> +++ b/security/selinux/ss/mls.c
> @@ -492,6 +492,8 @@ int mls_convert_context(struct policydb *oldp,
>  			rc = ebitmap_set_bit(&bitmap, catdatum->value - 1, 1);
>  			if (rc)
>  				return rc;
> +
> +			cond_resched();
>  		}
>  		ebitmap_destroy(&c->range.level[l].cat);
>  		c->range.level[l].cat = bitmap;
> 

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