From: Andrea Arcangeli <aarcange@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>,
Andrea Righi <andrea@betterlinux.com>,
CAI Qian <caiqian@redhat.com>, Rik van Riel <riel@redhat.com>,
Mel Gorman <mel@csn.ul.ie>,
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: Fri, 3 Jun 2011 20:13:22 +0200 [thread overview]
Message-ID: <20110603181322.GN2802@random.random> (raw)
In-Reply-To: <alpine.LSU.2.00.1106030957090.1901@sister.anvils>
On Fri, Jun 03, 2011 at 10:06:14AM -0700, Hugh Dickins wrote:
> On Thu, 2 Jun 2011, Andrea Arcangeli wrote:
> > On Thu, Jun 02, 2011 at 10:29:39AM -0700, Hugh Dickins wrote:
> > > AndreaA, I didn't study the patch you posted half an hour ago,
> > > since by that time I'd worked it out and was preparing patch below.
> > > I think your patch would be for a different bug, hopefully one we
> > > don't have, it looks more complicated than we should need for this.
> >
> > I didn't expect two different bugs leading to double free.
>
> There wasn't a double free there, just failure to cope with race
> emptying the list, so accessing head when expecting a full entry.
Yes, we thought it was a double free initially because of two dead
pointers but we couldn't explain why mm was null so consistently.
> You'll see from the "beware" comment in scan_get_next_rmap_item()
> that this case is expected, that it sometimes reaches freeing the
> slots before the exiting task reaches __ksm_exit().
>
> That race should already be handled. I believe your patch is unnecessary,
> because get_mm_slot() is a hashlist lookup, and will return NULL once
> either end has done the hlist_del(&mm_slot->link).
Ok so that case is handled by get_mm_slot not succeeding. I see thanks
for the review.
next prev parent reply other threads:[~2011-06-03 18:13 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 [this message]
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 ` [BUG 3.0.0-rc1] ksm: NULL pointer dereference in ksm_do_scan() Andrea Righi
2011-06-03 4:42 ` 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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