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: Thu, 2 Jun 2011 19:43:05 +0200 [thread overview]
Message-ID: <20110602174305.GH19505@random.random> (raw)
In-Reply-To: <alpine.LSU.2.00.1106021011300.1277@sister.anvils>
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.
If you've time please review my other patch too because mmput runs
with no mmap_sem hold and I think the ksm scan code runs under the
assumption that __ksm_exit is waiting in down_write() when
ksm_mmlist_lock is released (before freeing the mm_slot), and that
assumption is wrong. ksm_test_exit may very well be true despite
__ksm_exit didn't run yet, and ksm scan will proceed freeing after
changing the mm_slot and ksm_exit will be free to run and free again
immediately after the ksm scan releases the ksm_mmlist_lock and before
it clears the MMF_VM_MERGEABLE (because the mm_slot has been changed
before releasing the ksm_mmlist_lock).
The rmap_list being null will kind of hide it, the fact there's so
little time between the unlock of the ksm_mmlist_lock and the clearing
of MMF_VM_MERGEABLE (that will stop ksm_exit from calling __ksm_exit
at all) will also hide it. At least in
unmerge_and_remove_all_rmap_items remove_trailing_rmap_items will nuke
the rmap_list just before this race runs so making it more likely
possible.
next prev parent reply other threads:[~2011-06-02 17:44 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 [this message]
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 ` [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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