From: Andrea Righi <andrea@betterlinux.com>
To: Chris Wright <chrisw@sous-sol.org>
Cc: CAI Qian <caiqian@redhat.com>, Hugh Dickins <hughd@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>,
Izik Eidus <ieidus@redhat.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [BUG 3.0.0-rc1] ksm: NULL pointer dereference in ksm_do_scan()
Date: Thu, 2 Jun 2011 22:10:48 +0200 [thread overview]
Message-ID: <20110602201048.GA4114@thinkpad> (raw)
In-Reply-To: <20110602164841.GK23047@sequoia.sous-sol.org>
On Thu, Jun 02, 2011 at 09:48:41AM -0700, Chris Wright wrote:
> * Andrea Righi (andrea@betterlinux.com) wrote:
> > mmh.. I can reproduce the bug also with the standard ubuntu (11.04)
> > kernel. Could you post your .config?
>
> Andrea (Righi), can you tell me if this WARN fires? This looks
> like a pure race between removing from list and checking list, i.e.
> insufficient locking.
Yes, it does. With this patch:
[ 50.968896] WARNING: at mm/ksm.c:1305 ksm_scan_thread+0x9e3/0xe50()
>
> ksm_scan.mm_slot == the only registered mm
>
> CPU 1 (bug program) CPU 2 (ksmd)
> list_empty() is false
> lock
> ksm_scan.mm_slot
> list_del
> unlock
> slot == &ksm_mm_head (but list is now empty_)
It seems to be the exact problem.
-Andrea
>
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 942dfc7..ab79a92 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1301,6 +1301,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
> slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
> ksm_scan.mm_slot = slot;
> spin_unlock(&ksm_mmlist_lock);
> + WARN_ON(slot == &ksm_mm_head);
> next_mm:
> ksm_scan.address = 0;
> ksm_scan.rmap_list = &slot->rmap_list;
next prev parent reply other threads:[~2011-06-02 20:10 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-01 22:20 [BUG 3.0.0-rc1] ksm: NULL pointer dereference in ksm_do_scan() Andrea Righi
2011-06-02 1:53 ` Chris Wright
2011-06-02 7:09 ` CAI Qian
2011-06-02 14:19 ` Andrea Righi
2011-06-02 16:48 ` Chris Wright
2011-06-02 17:29 ` Hugh Dickins
2011-06-02 17:43 ` Andrea Arcangeli
2011-06-03 17:06 ` Hugh Dickins
2011-06-03 18:13 ` Andrea Arcangeli
2011-06-02 17:35 ` [PATCH] ksm: fix race between ksmd and exiting task Chris Wright
2011-06-02 20:12 ` Andrea Righi
2011-06-02 21:23 ` Chris Wright
2011-06-03 16:37 ` Hugh Dickins
2011-06-04 0:54 ` [PATCH] ksm: fix NULL pointer dereference in scan_get_next_rmap_item Chris Wright
2011-06-02 20:10 ` Andrea Righi [this message]
2011-06-03 4:42 ` [BUG 3.0.0-rc1] ksm: NULL pointer dereference in ksm_do_scan() CAI Qian
2011-06-02 14:31 ` Chris Wright
2011-06-02 14:36 ` Andrea Arcangeli
2011-06-02 15:36 ` Chris Wright
2011-06-02 16:44 ` Andrea Arcangeli
2011-06-02 20:15 ` Andrea Righi
2011-06-02 21:35 ` Andrea Arcangeli
2011-06-03 4:50 ` CAI Qian
2011-06-03 4:44 ` CAI Qian
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