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From: Dan Williams <dan.j.williams@intel.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Linux MM <linux-mm@kvack.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Steve Capper <steve.capper@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Borislav Petkov <bp@alien8.de>, Rik van Riel <riel@redhat.com>,
	Dann Frazier <dann.frazier@canonical.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Michal Hocko <mhocko@suse.cz>,
	linux-tip-commits@vger.kernel.org
Subject: Re: get_zone_device_page() in get_page() and page_cache_get_speculative()
Date: Mon, 24 Apr 2017 10:23:59 -0700	[thread overview]
Message-ID: <CAPcyv4i8mBOCuA8k-A8RXGMibbnqHUsa3Ly+YcQbr0eCdjruUw@mail.gmail.com> (raw)
In-Reply-To: <20170423233125.nehmgtzldgi25niy@node.shutemov.name>

On Sun, Apr 23, 2017 at 4:31 PM, Kirill A. Shutemov
<kirill@shutemov.name> wrote:
> On Thu, Apr 20, 2017 at 02:46:51PM -0700, Dan Williams wrote:
>> On Sat, Mar 18, 2017 at 2:52 AM, tip-bot for Kirill A. Shutemov
>> <tipbot@zytor.com> wrote:
>> > Commit-ID:  2947ba054a4dabbd82848728d765346886050029
>> > Gitweb:     http://git.kernel.org/tip/2947ba054a4dabbd82848728d765346886050029
>> > Author:     Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> > AuthorDate: Fri, 17 Mar 2017 00:39:06 +0300
>> > Committer:  Ingo Molnar <mingo@kernel.org>
>> > CommitDate: Sat, 18 Mar 2017 09:48:03 +0100
>> >
>> > x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation
>> >
>> > This patch provides all required callbacks required by the generic
>> > get_user_pages_fast() code and switches x86 over - and removes
>> > the platform specific implementation.
>> >
>> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> > Cc: Andrew Morton <akpm@linux-foundation.org>
>> > Cc: Aneesh Kumar K . V <aneesh.kumar@linux.vnet.ibm.com>
>> > Cc: Borislav Petkov <bp@alien8.de>
>> > Cc: Catalin Marinas <catalin.marinas@arm.com>
>> > Cc: Dann Frazier <dann.frazier@canonical.com>
>> > Cc: Dave Hansen <dave.hansen@intel.com>
>> > Cc: H. Peter Anvin <hpa@zytor.com>
>> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
>> > Cc: Peter Zijlstra <peterz@infradead.org>
>> > Cc: Rik van Riel <riel@redhat.com>
>> > Cc: Steve Capper <steve.capper@linaro.org>
>> > Cc: Thomas Gleixner <tglx@linutronix.de>
>> > Cc: linux-arch@vger.kernel.org
>> > Cc: linux-mm@kvack.org
>> > Link: http://lkml.kernel.org/r/20170316213906.89528-1-kirill.shutemov@linux.intel.com
>> > [ Minor readability edits. ]
>> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
>>
>> I'm still trying to spot the bug, but bisect points to this patch as
>> the point at which my unit tests start failing with the following
>> signature:
>>
>> [   35.423841] WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155
>> percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
>
> Okay, I've tracked it down. The issue is triggered by replacment
> get_page() with page_cache_get_speculative().
>
> page_cache_get_speculative() doesn't have get_zone_device_page(). :-|
>
> And I think it's your bug, Dan: it's wrong to have
> get_/put_zone_device_page() in get_/put_page(). I must be handled by
> page_ref_* machinery to catch all cases where we manipulate with page
> refcount.

The page_ref conversion landed in 4.6 *after* the ZONE_DEVICE
implementation that landed in 4.5, so there was a missed conversion of
the zone-device reference counting to page_ref.

> Back to the big picture:
>
> I hate that we need to have such additional code in page refcount
> primitives. I worked hard to remove compound page ugliness from there and
> now zone_device creeping in...
>
> Is it the only option?

Not sure, I need to spend some time to understand what page_ref means
to ZONE_DEVICE.

  reply	other threads:[~2017-04-24 17:24 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-20 21:46 [tip:x86/mm] x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation Dan Williams
2017-04-21 14:16 ` Kirill A. Shutemov
2017-04-21 19:30   ` Dan Williams
2017-04-23  9:52     ` [PATCH] Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation" Ingo Molnar
2017-04-23 23:31 ` get_zone_device_page() in get_page() and page_cache_get_speculative() Kirill A. Shutemov
2017-04-24 17:23   ` Dan Williams [this message]
2017-04-24 17:30     ` Kirill A. Shutemov
2017-04-24 17:47       ` Dan Williams
2017-04-24 18:01         ` Kirill A. Shutemov
2017-04-24 18:25           ` Kirill A. Shutemov
2017-04-24 18:41             ` Dan Williams
2017-04-25 13:19               ` Kirill A. Shutemov
2017-04-25 16:44                 ` Dan Williams
2017-04-27  0:55   ` [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Dan Williams
2017-04-27  8:33     ` Kirill A. Shutemov
2017-04-28  6:39       ` Ingo Molnar
2017-04-28  8:14         ` [PATCH] mm, zone_device: Replace " Kirill A. Shutemov
2017-04-28 17:23         ` [PATCH v2] mm, zone_device: replace " Dan Williams
2017-04-28 17:34           ` Jerome Glisse
2017-04-28 17:41             ` Dan Williams
2017-04-28 18:00               ` Jerome Glisse
2017-04-28 19:02                 ` Dan Williams
2017-04-28 19:16                   ` Jerome Glisse
2017-04-28 19:22                     ` Dan Williams
2017-04-28 19:33                       ` Jerome Glisse
2017-04-29 10:17                         ` Kirill A. Shutemov
2017-04-30 23:14                           ` Jerome Glisse
2017-05-01  1:42                             ` Dan Williams
2017-05-01  1:54                               ` Jerome Glisse
2017-05-01  2:40                                 ` Dan Williams
2017-05-01  3:48                             ` Logan Gunthorpe
2017-05-01 10:23                             ` Kirill A. Shutemov
2017-05-01 13:55                               ` Jerome Glisse
2017-05-01 20:19                                 ` Dan Williams
2017-05-01 20:32                                   ` Jerome Glisse
2017-05-02 11:37                                 ` Kirill A. Shutemov
2017-05-02 13:22                                   ` Jerome Glisse
2017-04-29 14:18           ` Ingo Molnar
2017-05-01  2:45             ` Dan Williams
2017-05-01  7:12               ` Ingo Molnar
2017-05-01  9:33                 ` Kirill A. Shutemov
2017-05-01  8:28           ` [tip:x86/mm] mm, zone_device: Replace {get, put}_zone_device_page() with a single reference to fix pmem crash tip-bot for Dan Williams
2017-04-27 16:11     ` [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Logan Gunthorpe
2017-04-27 16:14       ` Dan Williams
2017-04-27 16:33         ` Logan Gunthorpe
2017-04-27 16:38           ` Dan Williams
2017-04-27 16:45             ` Logan Gunthorpe
2017-04-27 16:46               ` Dan Williams

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