From: "Huang\, Ying" <ying.huang@intel.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
<dan.carpenter@oracle.com>, <andrea.parri@amarulasolutions.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: Wed, 06 Feb 2019 08:14:35 +0800 [thread overview]
Message-ID: <878sytsrh0.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <alpine.LSU.2.11.1902041257390.4682@eggly.anvils> (Hugh Dickins's message of "Mon, 4 Feb 2019 13:37:00 -0800")
Hi, Hugh,
Hugh Dickins <hughd@google.com> writes:
> 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.
>
> The multiple dynamically allocated and freed swapper address spaces
> have indeed broken what used to make it safe. If those imaginary
> address spaces did not have to be virtually contiguous, I'd say
> cache them and reuse them, instead of freeing. But I don't see
> how to do that as it stands.
>
> find_get_page(swapper_address_space(entry), swp_offset(entry)) has
> become an unsafe construct, where it used to be safe against corrupted
> page tables. Maybe we don't care so much about crashing on corrupted
> page tables nowadays (I haven't heard recent complaints), and I think
> Huang is correct that lookup_swap_cache() and __read_swap_cache_async()
> happen to be the only instances that need to be guarded against swapoff
> (the others are working with page table locked).
>
> The array of arrays of swapper spaces is all just to get a separate
> lock for separate extents of the swapfile: I wonder whether Matthew has
> anything in mind for that in XArray (I think Peter once got it working
> in radix-tree, but the overhead not so good).
>
> (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.)
Thanks a lot for your review and comments!
It appears that you have no strong objection for this patch? Could I
have your "Acked-by"?
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2019-02-06 0:14 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=878sytsrh0.fsf@yhuang-dev.intel.com \
--to=ying.huang@intel.com \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=andrea.parri@amarulasolutions.com \
--cc=dan.carpenter@oracle.com \
--cc=daniel.m.jordan@oracle.com \
--cc=dave.hansen@linux.intel.com \
--cc=hughd@google.com \
--cc=kernel-janitors@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=osandov@fb.com \
--cc=paulmck@linux.ibm.com \
--cc=peterz@infradead.org \
--cc=sfr@canb.auug.org.au \
--cc=stern@rowland.harvard.edu \
--cc=tj@kernel.org \
--cc=will.deacon@arm.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).