From: Matthew Wilcox <willy@infradead.org>
To: Eric Dumazet <edumazet@google.com>
Cc: "Lech Perczak" <l.perczak@camlintechnologies.com>,
"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: Wed, 15 May 2019 08:18:14 -0700 [thread overview]
Message-ID: <20190515151814.GD31704@bombadil.infradead.org> (raw)
In-Reply-To: <CANn89iJ0r116a8q_+jUgP_8wPX4iS6WVppQ6HvgZFt9v9CviKA@mail.gmail.com>
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.
next prev parent reply other threads:[~2019-05-15 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 ` 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 [this message]
2019-05-16 15:18 ` Lech Perczak
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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