linux-kernel - Re: [PATCH] exit: fix oops in sync_mm

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:	Tue, 30 Mar 2010 18:22:58 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, cl@...ux-foundation.org,
	lee.schermerhorn@...com, rientjes@...gle.com,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Troels Liebe Bentsen <tlb@...anden.dk>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH] exit: fix oops in sync_mm_rss

On Wed, 31 Mar 2010 09:41:24 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> > With this fixed, the test for non-zero tsk->mm is't really needed in
> > do_exit(), is it?  I guess it makes sense though - sync_mm_rss() only
> > really works for kernel threads by luck..
> 
> At first, I considered so, too. But I changed my mind to show
> "we know tsk->mm can be NULL here!" by code. 
> Because __sync_mm_rss_stat() has BUG_ON(!mm), the code reader will think
> tsk->mm shouldn't be NULL always.
> 
> Doesn't make sense ?

uh, not really ;)


I think we should do this too:

--- a/mm/memory.c~exit-fix-oops-in-sync_mm_rss-fix
+++ a/mm/memory.c
@@ -131,7 +131,6 @@ static void __sync_task_rss_stat(struct 
 
 	for (i = 0; i < NR_MM_COUNTERS; i++) {
 		if (task->rss_stat.count[i]) {
-			BUG_ON(!mm);
 			add_mm_counter(mm, i, task->rss_stat.count[i]);
 			task->rss_stat.count[i] = 0;
 		}
_

Because we just made sure it can't happen, and if it _does_ happen, the
oops will tell us the samme thing that the BUG_ON() would have.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/