From: Lech Perczak <l.perczak@camlintechnologies.com>
To: Matthew Wilcox <willy@infradead.org>, Eric Dumazet <edumazet@google.com>
Cc: "Al Viro" <viro@zeniv.linux.org.uk>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Piotr Figiel" <p.figiel@camlintechnologies.com>,
"Krzysztof Drobiński" <k.drobinski@camlintechnologies.com>,
"Pawel Lenkow" <p.lenkow@camlintechnologies.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Subject: Re: Recurring warning in page_copy_sane (inside copy_page_to_iter) when running stress tests involving drop_caches
Date: Thu, 16 May 2019 15:18:23 +0000 [thread overview]
Message-ID: <79c406af-3cc4-1e63-80d5-267900520ef8@camlintechnologies.com> (raw)
In-Reply-To: <20190515151814.GD31704@bombadil.infradead.org>
W dniu 15.05.2019 o 17:18, Matthew Wilcox pisze:
> On Wed, May 15, 2019 at 08:02:17AM -0700, Eric Dumazet wrote:
>> On Wed, May 15, 2019 at 7:43 AM Matthew Wilcox <willy@infradead.org> wrote:
>>> You're seeing a race between page_address(page) being called twice.
>>> Between those two calls, something has caused the page to be removed from
>>> the page_address_map() list. Eric's patch avoids calling page_address(),
>>> so apply it and be happy.
>> Hmm... wont the kmap_atomic() done later, after page_copy_sane() would
>> suffer from the race ?
>>
>> It seems there is a real bug somewhere to fix.
> No. page_address() called before the kmap_atomic() will look through
> the list of mappings and see if that page is mapped somewhere. We unmap
> lazily, so all it takes to trigger this race is that the page _has_
> been mapped before, and its mapping gets torn down during this call.
>
> While the page is kmapped, its mapping cannot be torn down.
And that's the answer I'm really glad to hear.
In the meantime I've set up a test run with CONFIG_HIGHMEM disabled
to be extra sure, however quite expectedly it robs the system of 256MiB
of accessible memory.
Unfortunatly, looking through defconfigs for 32-bit ARM, CONFIG_HIGHMEM
is enabled in quite a few of them, i.MX included.
I'll pick up the patch then and drop it when it gets included in 4.19.y.
Thanks!
--
With kind regards,
Lech
next prev parent reply other threads:[~2019-05-16 15:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <d68c83ba-bf5a-f6e8-44dd-be98f45fc97a@camlintechnologies.com>
2019-04-26 8:42 ` Recurring warning in page_copy_sane (inside copy_page_to_iter) when running stress tests involving drop_caches Lech Perczak
2019-05-15 13:18 ` Lech Perczak
2019-05-15 14:43 ` Matthew Wilcox
2019-05-15 15:02 ` Eric Dumazet
2019-05-15 15:18 ` Matthew Wilcox
2019-05-16 15:18 ` Lech Perczak [this message]
2019-05-15 15:04 ` Greg Kroah-Hartman
2019-05-15 15:20 ` Matthew Wilcox
2019-05-15 15:37 ` Greg Kroah-Hartman
2019-05-20 11:05 ` Greg Kroah-Hartman
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