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From: Jan Kara <jack@suse.cz>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Leon Romanovsky" <leon@kernel.org>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Dave Chinner" <david@fromorbit.com>,
	"David Airlie" <airlied@linux.ie>,
	"David S . Miller" <davem@davemloft.net>,
	"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
	kvm@vger.kernel.org, linux-block@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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	netdev@vger.kernel.org, linux-mm@kvack.org,
	LKML <linux-kernel@vger.kernel.org>,
	"Maor Gottlieb" <maorg@mellanox.com>,
	"Ran Rozenstein" <ranro@mellanox.com>
Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN
Date: Mon, 6 Jan 2020 10:01:47 +0100	[thread overview]
Message-ID: <20200106090147.GA9176@quack2.suse.cz> (raw)
In-Reply-To: <612aa292-ec45-295c-b56c-c622876620fa@nvidia.com>

On Sat 28-12-19 20:33:32, John Hubbard wrote:
> On 12/27/19 1:56 PM, John Hubbard wrote:
> ...
> >> It is ancient verification test (~10y) which is not an easy task to
> >> make it understandable and standalone :).
> >>
> > 
> > Is this the only test that fails, btw? No other test failures or hints of
> > problems?
> > 
> > (Also, maybe hopeless, but can *anyone* on the RDMA list provide some
> > characterization of the test, such as how many pins per page, what page
> > sizes are used? I'm still hoping to write a test to trigger something
> > close to this...)
> > 
> > I do have a couple more ideas for test runs:
> > 
> > 1. Reduce GUP_PIN_COUNTING_BIAS to 1. That would turn the whole override of
> > page->_refcount into a no-op, and so if all is well (it may not be!) with the
> > rest of the patch, then we'd expect this problem to not reappear.
> > 
> > 2. Active /proc/vmstat *foll_pin* statistics unconditionally (just for these
> > tests, of course), so we can see if there is a get/put mismatch. However, that
> > will change the timing, and so it must be attempted independently of (1), in
> > order to see if it ends up hiding the repro.
> > 
> > I've updated this branch to implement (1), but not (2), hoping you can give
> > this one a spin?
> > 
> >     git@github.com:johnhubbard/linux.git  pin_user_pages_tracking_v11_with_diags
> > 
> > 
> 
> Also, looking ahead:
> 
> a) if the problem disappears with the latest above test, then we likely have
>    a huge page refcount overflow, and there are a couple of different ways to
>    fix it. 
> 
> b) if it still reproduces with the above, then it's some other random mistake,
>    and in that case I'd be inclined to do a sort of guided (or classic, unguided)
>    git bisect of the series. Because it could be any of several patches.
> 
>    If that's too much trouble, then I'd have to fall back to submitting a few
>    patches at a time and working my way up to the tracking patch...

It could also be that an ordinary page reference is dropped with 'unpin'
thus underflowing the page refcount...

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2020-01-06  9:02 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-16 22:25 [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-12-16 22:25 ` [PATCH v11 01/25] mm/gup: factor out duplicate code from four routines John Hubbard
2019-12-18 15:52   ` Kirill A. Shutemov
2019-12-18 22:15     ` John Hubbard
2019-12-18 22:45       ` Kirill A. Shutemov
2019-12-16 22:25 ` [PATCH v11 02/25] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-12-16 22:25 ` [PATCH v11 03/25] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-12-16 22:25 ` [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-12-18 16:04   ` Kirill A. Shutemov
2019-12-19  0:32     ` John Hubbard
2019-12-19  0:40     ` [PATCH v12] " John Hubbard
2019-12-19  5:27   ` [PATCH v11 04/25] " Dan Williams
2019-12-19  5:48     ` John Hubbard
2019-12-19  6:52       ` Dan Williams
2019-12-19  7:33         ` John Hubbard
2019-12-16 22:25 ` [PATCH v11 05/25] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-12-16 22:25 ` [PATCH v11 06/25] mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM John Hubbard
2019-12-18 16:19   ` Kirill A. Shutemov
2019-12-18 22:15     ` John Hubbard
2019-12-16 22:25 ` [PATCH v11 07/25] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call John Hubbard
2019-12-16 22:25 ` [PATCH v11 08/25] mm/gup: allow FOLL_FORCE for get_user_pages_fast() John Hubbard
2019-12-16 22:25 ` [PATCH v11 09/25] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-12-16 22:25 ` [PATCH v11 10/25] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-12-16 22:25 ` [PATCH v11 11/25] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-16 22:25 ` [PATCH v11 12/25] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-12-16 22:25 ` [PATCH v11 13/25] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-12-16 22:25 ` [PATCH v11 14/25] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-12-16 22:25 ` [PATCH v11 15/25] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-12-16 22:25 ` [PATCH v11 16/25] net/xdp: " John Hubbard
2019-12-16 22:25 ` [PATCH v11 17/25] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-12-16 22:25 ` [PATCH v11 18/25] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-12-16 22:25 ` [PATCH v11 19/25] vfio, mm: " John Hubbard
2019-12-16 22:25 ` [PATCH v11 20/25] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-16 22:25 ` [PATCH v11 21/25] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-12-16 22:25 ` [PATCH v11 22/25] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard
2019-12-16 22:25 ` [PATCH v11 23/25] mm/gup: track FOLL_PIN pages John Hubbard
2019-12-17 14:19   ` [PATCH v12 " John Hubbard
2019-12-16 22:25 ` [PATCH v11 24/25] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-12-16 22:25 ` [PATCH v11 25/25] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-12-17  7:39 ` [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN Jan Kara
2019-12-19 13:26 ` Leon Romanovsky
2019-12-19 20:30   ` John Hubbard
2019-12-19 21:07     ` Jason Gunthorpe
2019-12-19 21:13       ` John Hubbard
2019-12-20 13:34         ` Jason Gunthorpe
2019-12-21  0:32           ` Dan Williams
2019-12-23 18:24             ` Jason Gunthorpe
2019-12-19 22:58       ` John Hubbard
2019-12-20 18:48         ` Leon Romanovsky
2019-12-20 23:13           ` John Hubbard
2019-12-20 18:29       ` Leon Romanovsky
2019-12-20 23:54         ` John Hubbard
2019-12-21 10:08           ` Leon Romanovsky
2019-12-21 23:59             ` John Hubbard
2019-12-22 13:23           ` Leon Romanovsky
2019-12-25  2:03             ` John Hubbard
2019-12-25  5:26               ` Leon Romanovsky
2019-12-27 21:56                 ` John Hubbard
2019-12-29  4:33                   ` John Hubbard
2020-01-06  9:01                     ` Jan Kara [this message]
2020-01-07  1:26                       ` John Hubbard
2019-12-20  9:21     ` Jan Kara
2019-12-21  0:02       ` John Hubbard
2019-12-21  0:33       ` Dan Williams
2019-12-21  0:41         ` John Hubbard
2019-12-21  0:51           ` Dan Williams
2019-12-21  0:53             ` John Hubbard

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