From: "Huang\, Ying" <ying.huang@intel.com>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
<dan.carpenter@oracle.com>, <dave.hansen@linux.intel.com>,
<sfr@canb.auug.org.au>, <osandov@fb.com>, <tj@kernel.org>,
<ak@linux.intel.com>, <linux-mm@kvack.org>,
<kernel-janitors@vger.kernel.org>, <paulmck@linux.ibm.com>,
<stern@rowland.harvard.edu>, <peterz@infradead.org>,
<willy@infradead.org>, <will.deacon@arm.com>
Subject: Re: About swapoff race patch (was Re: [PATCH] mm, swap: bounds check swap_info accesses to avoid NULL derefs)
Date: Mon, 11 Feb 2019 09:02:45 +0800 [thread overview]
Message-ID: <87sgwvqgqy.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20190207234244.GA6429@andrea> (Andrea Parri's message of "Fri, 8 Feb 2019 01:28:29 +0100")
Andrea Parri <andrea.parri@amarulasolutions.com> writes:
> Hi Huang, Ying,
>
> On Mon, Feb 04, 2019 at 01:37:00PM -0800, Hugh Dickins wrote:
>> On Thu, 31 Jan 2019, Andrew Morton wrote:
>> > On Thu, 31 Jan 2019 10:48:29 +0800 "Huang\, Ying" <ying.huang@intel.com> wrote:
>> > > Andrew Morton <akpm@linux-foundation.org> writes:
>> > > > mm-swap-fix-race-between-swapoff-and-some-swap-operations.patch is very
>> > > > stuck so can you please redo this against mainline?
>> > >
>> > > Allow me to be off topic, this patch has been in mm tree for quite some
>> > > time, what can I do to help this be merged upstream?
>
> [...]
>
>
>>
>> Wow, yes, it's about a year old.
>>
>> >
>> > I have no evidence that it has been reviewed, for a start. I've asked
>> > Hugh to look at it.
>>
>> I tried at the weekend. Usual story: I don't like it at all, the
>> ever-increasing complexity there, but certainly understand the need
>> for that fix, and have not managed to think up anything better -
>> and now I need to switch away, sorry.
>
> FWIW, I do agree with Hugh about "the need for that fix": AFAIU, that
> (mainline) code is naively buggy _and_ "this patch":
>
> http://lkml.kernel.org/r/20180223060010.954-1-ying.huang@intel.com
>
> "redone on top of mainline" seems both correct and appropriate to me.
Thanks! Because the patch needs to go through -mm tree, so I will
rebase the patch on top of the head of -mm tree.
>
>> (I was originally horrified by the stop_machine() added in swapon and
>> swapoff, but perhaps I'm remembering a distant past of really stopping
>> the machine: stop_machine() today looked reasonable, something to avoid
>> generally like lru_add_drain_all(), but not as shameful as I thought.)
>
> AFAIC_find_on_LKML, we have three different fixes (at least!): resp.,
>
> 1. refcount(-based),
> 2. RCU,
> 3. stop_machine();
>
> (3) appears to be the less documented/relied-upon/tested among these;
> I'm not aware of definitive reasons forcing us to reject (1) and (2).
Because swapoff() is a really cold path, while page fault handler is a
really hot path. (3) can minimize the overhead of the hot path.
Best Regards,
Huang, Ying
> Andrea
>
>
>>
>> Hugh
next prev parent reply other threads:[~2019-02-11 1:02 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-11 9:59 [PATCH] mm, swap: Potential NULL dereference in get_swap_page_of_type() Dan Carpenter
2019-01-11 17:41 ` Daniel Jordan
2019-01-11 23:20 ` Andrea Parri
2019-01-14 22:25 ` Daniel Jordan
2019-01-15 0:23 ` [PATCH] mm, swap: bounds check swap_info accesses to avoid NULL derefs Daniel Jordan
2019-01-15 1:17 ` Andrea Parri
2019-01-30 6:26 ` Andrew Morton
2019-01-31 1:52 ` Daniel Jordan
2019-01-31 2:44 ` [PATCH v2] mm, swap: bounds check swap_info array " Daniel Jordan
2019-01-31 2:48 ` About swapoff race patch (was Re: [PATCH] mm, swap: bounds check swap_info accesses to avoid NULL derefs) Huang, Ying
2019-01-31 20:46 ` Andrew Morton
2019-02-02 7:14 ` Huang, Ying
2019-02-04 21:37 ` Hugh Dickins
2019-02-04 22:26 ` Matthew Wilcox
2019-02-06 0:14 ` Huang, Ying
2019-02-06 0:36 ` Hugh Dickins
2019-02-06 0:58 ` Huang, Ying
2019-02-08 0:28 ` Andrea Parri
2019-02-11 1:02 ` Huang, Ying [this message]
2019-01-30 7:28 ` [PATCH] mm, swap: bounds check swap_info accesses to avoid NULL derefs Dan Carpenter
2019-01-31 1:55 ` Daniel Jordan
2019-01-30 9:13 ` Peter Zijlstra
2019-01-31 2:00 ` Daniel Jordan
2019-01-15 0:28 ` [PATCH] mm, swap: Potential NULL dereference in get_swap_page_of_type() Andrea Parri
2019-01-14 2:12 ` Huang, Ying
2019-01-14 2:12 ` Huang, Ying
2019-01-14 8:43 ` Dan Carpenter
2019-01-14 23:40 ` Daniel Jordan
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