linux-kernel - Re: linux-next crash during very early boot

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 14 Apr 2016 10:35:47 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Valdis Kletnieks <Valdis.Kletnieks@...edu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: linux-next crash during very early boot

On Wed, Apr 13, 2016 at 08:29:46PM -0400, Valdis Kletnieks wrote:
> I'm seeing my laptop crash/wedge up/something during very early
> boot - before it can write anything to the console.  Nothing in pstore,
> need to hold down the power button for 6 seconds and reboot.
> 
> git bisect points at:
> 
> commit 7a6bacb133752beacb76775797fd550417e9d3a2
> Author: Joonsoo Kim <iamjoonsoo.kim@....com>
> Date:   Thu Apr 7 13:59:39 2016 +1000
> 
>     mm/slab: factor out kmem_cache_node initialization code
> 
>     It can be reused on other place, so factor out it.  Following patch will
>     use it.
> 
> 
> Not sure what the problem is - the logic *looks* ok at first read.  The
> patch *does* remove a spin_lock_irq() - but I find it difficult to
> believe that with it gone, my laptop is able to hit the race condition
> the spinlock protects against *every single boot*.
> 
> The only other thing I see is that n->free_limit used to be assigned
> every time, and now it's only assigned at initial creation.

Hello,

My fault. It should be assgined every time. Please test below patch.
I will send it with proper SOB after you confirm the problem disappear.
Thanks for report and analysis!

Thanks.

---------------->8-----------------
diff --git a/mm/slab.c b/mm/slab.c
index 13e74aa..59dd94a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -856,8 +856,14 @@ static int init_cache_node(struct kmem_cache *cachep, int node, gfp_t gfp)
 	 * node has not already allocated this
 	 */
 	n = get_node(cachep, node);
-	if (n)
+	if (n) {
+		spin_lock_irq(&n->list_lock);
+		n->free_limit = (1 + nr_cpus_node(node)) * cachep->batchcount +
+				cachep->num;
+		spin_unlock_irq(&n->list_lock);
+
 		return 0;
+	}
 
 	n = kmalloc_node(sizeof(struct kmem_cache_node), gfp, node);
 	if (!n)