From: Jan Kara <jack@suse.cz>
To: Ira Weiny <ira.weiny@intel.com>
Cc: "Jeff Layton" <jlayton@kernel.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Jan Kara" <jack@suse.cz>, "Theodore Ts'o" <tytso@mit.edu>,
"Dave Chinner" <david@fromorbit.com>,
"Matthew Wilcox" <willy@infradead.org>,
linux-xfs@vger.kernel.org,
"Andrew Morton" <akpm@linux-foundation.org>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH RFC 02/10] fs/locks: Export F_LAYOUT lease to user space
Date: Wed, 12 Jun 2019 11:46:34 +0200 [thread overview]
Message-ID: <20190612094634.GA14578@quack2.suse.cz> (raw)
In-Reply-To: <20190611213812.GC14336@iweiny-DESK2.sc.intel.com>
On Tue 11-06-19 14:38:13, Ira Weiny wrote:
> On Sun, Jun 09, 2019 at 09:00:24AM -0400, Jeff Layton wrote:
> > On Wed, 2019-06-05 at 18:45 -0700, ira.weiny@intel.com wrote:
> > > From: Ira Weiny <ira.weiny@intel.com>
> > >
> > > GUP longterm pins of non-pagecache file system pages (eg FS DAX) are
> > > currently disallowed because they are unsafe.
> > >
> > > The danger for pinning these pages comes from the fact that hole punch
> > > and/or truncate of those files results in the pages being mapped and
> > > pinned by a user space process while DAX has potentially allocated those
> > > pages to other processes.
> > >
> > > Most (All) users who are mapping FS DAX pages for long term pin purposes
> > > (such as RDMA) are not going to want to deallocate these pages while
> > > those pages are in use. To do so would mean the application would lose
> > > data. So the use case for allowing truncate operations of such pages
> > > is limited.
> > >
> > > However, the kernel must protect itself and users from potential
> > > mistakes and/or malicious user space code. Rather than disabling long
> > > term pins as is done now. Allow for users who know they are going to
> > > be pinning this memory to alert the file system of this intention.
> > > Furthermore, allow users to be alerted such that they can react if a
> > > truncate operation occurs for some reason.
> > >
> > > Example user space pseudocode for a user using RDMA and wanting to allow
> > > a truncate would look like this:
> > >
> > > lease_break_sigio_handler() {
> > > ...
> > > if (sigio.fd == rdma_fd) {
> > > complete_rdma_operations(...);
> > > ibv_dereg_mr(mr);
> > > close(rdma_fd);
> > > fcntl(rdma_fd, F_SETLEASE, F_UNLCK);
> > > }
> > > }
> > >
> > > setup_rdma_to_dax_file() {
> > > ...
> > > rdma_fd = open(...)
> > > fcntl(rdma_fd, F_SETLEASE, F_LAYOUT);
> >
> > I'm not crazy about this interface. F_LAYOUT doesn't seem to be in the
> > same category as F_RDLCK/F_WRLCK/F_UNLCK.
> >
> > Maybe instead of F_SETLEASE, this should use new
> > F_SETLAYOUT/F_GETLAYOUT cmd values? There is nothing that would prevent
> > you from setting both a lease and a layout on a file, and indeed knfsd
> > can set both.
> >
> > This interface seems to conflate the two.
>
> I've been feeling the same way. This is why I was leaning toward a new lease
> type. I called it "F_LONGTERM" but the name is not important.
>
> I think the concept of adding "exclusive" to the layout lease can fix this
> because the NFS lease is non-exclusive where the user space one (for the
> purpose of GUP pinning) would need to be.
>
> FWIW I have not worked out exactly what this new "exclusive" code will look
> like. Jan said:
>
> "There actually is support for locks that are not broken after given
> timeout so there shouldn't be too many changes need."
>
> But I'm not seeing that for Lease code. So I'm working on something for the
> lease code now.
Yeah, sorry for misleading you. Somehow I thought that if lease_break_time
== 0, we will wait indefinitely but when checking the code again, that
doesn't seem to be the case.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-06-12 9:46 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-06 1:45 [PATCH RFC 00/10] RDMA/FS DAX truncate proposal ira.weiny
2019-06-06 1:45 ` [PATCH RFC 01/10] fs/locks: Add trace_leases_conflict ira.weiny
2019-06-09 12:52 ` Jeff Layton
2019-06-06 1:45 ` [PATCH RFC 02/10] fs/locks: Export F_LAYOUT lease to user space ira.weiny
2019-06-09 13:00 ` Jeff Layton
2019-06-11 21:38 ` Ira Weiny
2019-06-12 9:46 ` Jan Kara [this message]
2019-06-06 1:45 ` [PATCH RFC 03/10] mm/gup: Pass flags down to __gup_device_huge* calls ira.weiny
2019-06-06 6:18 ` Christoph Hellwig
2019-06-06 16:10 ` Ira Weiny
2019-06-06 1:45 ` [PATCH RFC 04/10] mm/gup: Ensure F_LAYOUT lease is held prior to GUP'ing pages ira.weiny
2019-06-06 1:45 ` [PATCH RFC 05/10] fs/ext4: Teach ext4 to break layout leases ira.weiny
2019-06-06 1:45 ` [PATCH RFC 06/10] fs/ext4: Teach dax_layout_busy_page() to operate on a sub-range ira.weiny
2019-06-06 1:45 ` [PATCH RFC 07/10] fs/ext4: Fail truncate if pages are GUP pinned ira.weiny
2019-06-06 10:58 ` Jan Kara
2019-06-06 16:17 ` Ira Weiny
2019-06-06 1:45 ` [PATCH RFC 08/10] fs/xfs: Teach xfs to use new dax_layout_busy_page() ira.weiny
2019-06-06 1:45 ` [PATCH RFC 09/10] fs/xfs: Fail truncate if pages are GUP pinned ira.weiny
2019-06-06 1:45 ` [PATCH RFC 10/10] mm/gup: Remove FOLL_LONGTERM DAX exclusion ira.weiny
2019-06-06 5:52 ` [PATCH RFC 00/10] RDMA/FS DAX truncate proposal John Hubbard
2019-06-06 17:11 ` Ira Weiny
2019-06-06 19:46 ` Jason Gunthorpe
2019-06-06 10:42 ` Jan Kara
2019-06-06 15:35 ` Dan Williams
2019-06-06 19:51 ` Jason Gunthorpe
2019-06-06 22:22 ` Ira Weiny
2019-06-07 10:36 ` Jan Kara
2019-06-07 12:17 ` Jason Gunthorpe
2019-06-07 14:52 ` Ira Weiny
2019-06-07 15:10 ` Jason Gunthorpe
2019-06-12 10:29 ` Jan Kara
2019-06-12 11:47 ` Jason Gunthorpe
2019-06-12 12:09 ` Jan Kara
2019-06-12 18:41 ` Dan Williams
2019-06-13 7:17 ` Jan Kara
2019-06-12 19:14 ` Jason Gunthorpe
2019-06-12 22:13 ` Ira Weiny
2019-06-12 22:54 ` Dan Williams
2019-06-12 23:33 ` Ira Weiny
2019-06-13 1:14 ` Dan Williams
2019-06-13 15:13 ` Jason Gunthorpe
2019-06-13 16:25 ` Dan Williams
2019-06-13 17:18 ` Jason Gunthorpe
2019-06-13 16:53 ` Dan Williams
2019-06-13 15:12 ` Jason Gunthorpe
2019-06-13 7:53 ` Jan Kara
2019-06-12 18:49 ` Dan Williams
2019-06-13 7:43 ` Jan Kara
2019-06-06 22:03 ` Ira Weiny
2019-06-06 22:26 ` Ira Weiny
2019-06-06 22:28 ` Dave Chinner
2019-06-07 11:04 ` Jan Kara
2019-06-07 18:25 ` Ira Weiny
2019-06-07 18:50 ` Jason Gunthorpe
2019-06-08 0:10 ` Dave Chinner
2019-06-09 1:29 ` Ira Weiny
2019-06-12 12:37 ` Matthew Wilcox
2019-06-12 23:30 ` Ira Weiny
2019-06-13 0:55 ` Dave Chinner
2019-06-13 20:34 ` Ira Weiny
2019-06-14 3:42 ` Dave Chinner
2019-06-13 0:25 ` Dave Chinner
2019-06-13 3:23 ` Matthew Wilcox
2019-06-13 4:36 ` Dave Chinner
2019-06-13 10:47 ` Matthew Wilcox
2019-06-13 15:29 ` Jason Gunthorpe
2019-06-13 15:27 ` Matthew Wilcox
2019-06-13 21:13 ` Ira Weiny
2019-06-13 23:45 ` Jason Gunthorpe
2019-06-14 0:00 ` Ira Weiny
2019-06-14 2:09 ` Dave Chinner
2019-06-14 2:31 ` Matthew Wilcox
2019-06-14 3:07 ` Dave Chinner
2019-06-20 14:52 ` Jan Kara
2019-06-13 20:34 ` Ira Weiny
2019-06-14 2:58 ` Dave Chinner
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