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From: Ira Weiny <ira.weiny@intel.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Dan Williams <dan.j.williams@intel.com>,
	Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
	Theodore Ts'o <tytso@mit.edu>, John Hubbard <jhubbard@nvidia.com>,
	Michal Hocko <mhocko@suse.com>,
	linux-xfs@vger.kernel.org, linux-rdma@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [RFC PATCH v2 02/19] fs/locks: Add Exclusive flag to user Layout lease
Date: Thu, 29 Aug 2019 16:34:08 -0700	[thread overview]
Message-ID: <20190829233408.GD18249@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <e6f4f619967f4551adb5003d0364770fde2b8110.camel@kernel.org>

Missed this.  sorry.

On Mon, Aug 26, 2019 at 06:41:07AM -0400, Jeff Layton wrote:
> On Thu, 2019-08-15 at 07:56 +1000, Dave Chinner wrote:
> > On Wed, Aug 14, 2019 at 10:15:06AM -0400, Jeff Layton wrote:
> > > On Fri, 2019-08-09 at 15:58 -0700, ira.weiny@intel.com wrote:
> > > > From: Ira Weiny <ira.weiny@intel.com>
> > > > 
> > > > Add an exclusive lease flag which indicates that the layout mechanism
> > > > can not be broken.
> > > > 
> > > > Exclusive layout leases allow the file system to know that pages may be
> > > > GUP pined and that attempts to change the layout, ie truncate, should be
> > > > failed.
> > > > 
> > > > A process which attempts to break it's own exclusive lease gets an
> > > > EDEADLOCK return to help determine that this is likely a programming bug
> > > > vs someone else holding a resource.
> > .....
> > > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
> > > > index baddd54f3031..88b175ceccbc 100644
> > > > --- a/include/uapi/asm-generic/fcntl.h
> > > > +++ b/include/uapi/asm-generic/fcntl.h
> > > > @@ -176,6 +176,8 @@ struct f_owner_ex {
> > > >  
> > > >  #define F_LAYOUT	16      /* layout lease to allow longterm pins such as
> > > >  				   RDMA */
> > > > +#define F_EXCLUSIVE	32      /* layout lease is exclusive */
> > > > +				/* FIXME or shoudl this be F_EXLCK??? */
> > > >  
> > > >  /* operations for bsd flock(), also used by the kernel implementation */
> > > >  #define LOCK_SH		1	/* shared lock */
> > > 
> > > This interface just seems weird to me. The existing F_*LCK values aren't
> > > really set up to be flags, but are enumerated values (even if there are
> > > some gaps on some arches). For instance, on parisc and sparc:
> > 
> > I don't think we need to worry about this - the F_WRLCK version of
> > the layout lease should have these exclusive access semantics (i.e
> > other ops fail rather than block waiting for lease recall) and hence
> > the API shouldn't need a new flag to specify them.
> > 
> > i.e. the primary difference between F_RDLCK and F_WRLCK layout
> > leases is that the F_RDLCK is a shared, co-operative lease model
> > where only delays in operations will be seen, while F_WRLCK is a
> > "guarantee exclusive access and I don't care what it breaks"
> > model... :)
> > 
> 
> Not exactly...
> 
> F_WRLCK and F_RDLCK leases can both be broken, and will eventually time
> out if there is conflicting access. The F_EXCLUSIVE flag on the other
> hand is there to prevent any sort of lease break from 

Right EXCLUSIVE will not break for any reason.  It will fail truncate and hole
punch as we discussed back in June.  This is for the use case where the user
has handed this file/pages off to some hardware for which removing the lease
would be impossible.  _And_ we don't anticipate any valid use case that someone
will need to truncate short of killing the process to free up file system
space.

> 
> I'm guessing what Ira really wants with the F_EXCLUSIVE flag is
> something akin to what happens when we set fl_break_time to 0 in the
> nfsd code. nfsd never wants the locks code to time out a lease of any
> sort, since it handles that timeout itself.
> 
> If you're going to add this functionality, it'd be good to also convert
> knfsd to use it as well, so we don't end up with multiple ways to deal
> with that situation.

Could you point me at the source for knfsd?  I looked in 

git://git.linux-nfs.org/projects/steved/nfs-utils.git

but I don't see anywhere leases are used in that source?

Thanks,
Ira


  reply	other threads:[~2019-08-29 23:34 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09 22:58 [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-) ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 01/19] fs/locks: Export F_LAYOUT lease to user space ira.weiny
2019-08-09 23:52   ` Dave Chinner
2019-08-12 17:36     ` Ira Weiny
2019-08-14  8:05       ` Dave Chinner
2019-08-14 11:21         ` Jeff Layton
2019-08-14 11:38           ` Dave Chinner
2019-08-09 22:58 ` [RFC PATCH v2 02/19] fs/locks: Add Exclusive flag to user Layout lease ira.weiny
2019-08-14 14:15   ` Jeff Layton
2019-08-14 21:56     ` Dave Chinner
2019-08-26 10:41       ` Jeff Layton
2019-08-29 23:34         ` Ira Weiny [this message]
2019-09-04 12:52           ` Jeff Layton
2019-09-04 23:12   ` John Hubbard
2019-08-09 22:58 ` [RFC PATCH v2 03/19] mm/gup: Pass flags down to __gup_device_huge* calls ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 04/19] mm/gup: Ensure F_LAYOUT lease is held prior to GUP'ing pages ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 05/19] fs/ext4: Teach ext4 to break layout leases ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 06/19] fs/ext4: Teach dax_layout_busy_page() to operate on a sub-range ira.weiny
2019-08-23 15:18   ` Vivek Goyal
2019-08-29 18:52     ` Ira Weiny
2019-08-09 22:58 ` [RFC PATCH v2 07/19] fs/xfs: Teach xfs to use new dax_layout_busy_page() ira.weiny
2019-08-09 23:30   ` Dave Chinner
2019-08-12 18:05     ` Ira Weiny
2019-08-14  8:04       ` Dave Chinner
2019-08-09 22:58 ` [RFC PATCH v2 08/19] fs/xfs: Fail truncate if page lease can't be broken ira.weiny
2019-08-09 23:22   ` Dave Chinner
2019-08-12 18:08     ` Ira Weiny
2019-08-09 22:58 ` [RFC PATCH v2 09/19] mm/gup: Introduce vaddr_pin structure ira.weiny
2019-08-10  0:06   ` John Hubbard
2019-08-09 22:58 ` [RFC PATCH v2 10/19] mm/gup: Pass a NULL vaddr_pin through GUP fast ira.weiny
2019-08-10  0:06   ` John Hubbard
2019-08-09 22:58 ` [RFC PATCH v2 11/19] mm/gup: Pass follow_page_context further down the call stack ira.weiny
2019-08-10  0:18   ` John Hubbard
2019-08-12 19:01     ` Ira Weiny
2019-08-09 22:58 ` [RFC PATCH v2 12/19] mm/gup: Prep put_user_pages() to take an vaddr_pin struct ira.weiny
2019-08-10  0:30   ` John Hubbard
2019-08-12 20:46     ` Ira Weiny
2019-08-09 22:58 ` [RFC PATCH v2 13/19] {mm,file}: Add file_pins objects ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 14/19] fs/locks: Associate file pins while performing GUP ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 15/19] mm/gup: Introduce vaddr_pin_pages() ira.weiny
2019-08-10  0:09   ` John Hubbard
2019-08-12 21:00     ` Ira Weiny
2019-08-12 21:20       ` John Hubbard
2019-08-11 23:07   ` John Hubbard
2019-08-12 21:01     ` Ira Weiny
2019-08-12 12:28   ` Jason Gunthorpe
2019-08-12 21:48     ` Ira Weiny
2019-08-13 11:47       ` Jason Gunthorpe
2019-08-13 17:46         ` Ira Weiny
2019-08-13 17:56           ` John Hubbard
2019-08-09 22:58 ` [RFC PATCH v2 16/19] RDMA/uverbs: Add back pointer to system file object ira.weiny
2019-08-12 13:00   ` Jason Gunthorpe
2019-08-12 17:28     ` Ira Weiny
2019-08-12 17:56       ` Jason Gunthorpe
2019-08-12 21:15         ` Ira Weiny
2019-08-13 11:48           ` Jason Gunthorpe
2019-08-13 17:41             ` Ira Weiny
2019-08-13 18:00               ` Jason Gunthorpe
2019-08-13 20:38                 ` Ira Weiny
2019-08-14 12:23                   ` Jason Gunthorpe
2019-08-14 17:50                     ` Ira Weiny
2019-08-14 18:15                       ` Jason Gunthorpe
2019-09-04 22:25                     ` Ira Weiny
2019-09-11  8:19                       ` Jason Gunthorpe
2019-08-09 22:58 ` [RFC PATCH v2 17/19] RDMA/umem: Convert to vaddr_[pin|unpin]* operations ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 18/19] {mm,procfs}: Add display file_pins proc ira.weiny
2019-08-09 22:58 ` [RFC PATCH v2 19/19] mm/gup: Remove FOLL_LONGTERM DAX exclusion ira.weiny
2019-08-14 10:17 ` [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-) Jan Kara
2019-08-14 18:08   ` Ira Weiny
2019-08-15 13:05     ` Jan Kara
2019-08-16 19:05       ` Ira Weiny
2019-08-16 23:20         ` [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ; -) Ira Weiny
2019-08-19  6:36           ` Jan Kara
2019-08-17  2:26         ` [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-) Dave Chinner
2019-08-19  6:34           ` Jan Kara
2019-08-19  9:24             ` Dave Chinner
2019-08-19 12:38               ` Jason Gunthorpe
2019-08-19 21:53                 ` Ira Weiny
2019-08-20  1:12                 ` Dave Chinner
2019-08-20 11:55                   ` Jason Gunthorpe
2019-08-21 18:02                     ` Ira Weiny
2019-08-21 18:13                       ` Jason Gunthorpe
2019-08-21 18:22                         ` John Hubbard
2019-08-21 18:57                         ` Ira Weiny
2019-08-21 19:06                           ` Ira Weiny
2019-08-21 19:48                           ` Jason Gunthorpe
2019-08-21 20:44                             ` Ira Weiny
2019-08-21 23:49                               ` Jason Gunthorpe
2019-08-23  3:23                               ` Dave Chinner
2019-08-23 12:04                                 ` Jason Gunthorpe
2019-08-24  0:11                                   ` Dave Chinner
2019-08-24  5:08                                     ` Ira Weiny
2019-08-26  5:55                                       ` Dave Chinner
2019-08-29  2:02                                         ` Ira Weiny
2019-08-29  3:27                                           ` John Hubbard
2019-08-29 16:16                                             ` Ira Weiny
2019-09-02 22:26                                           ` Dave Chinner
2019-09-04 16:54                                             ` Ira Weiny
2019-08-25 19:39                                     ` Jason Gunthorpe
2019-08-24  4:49                                 ` Ira Weiny
2019-08-25 19:40                                   ` Jason Gunthorpe
2019-08-23  0:59                       ` Dave Chinner
2019-08-23 17:15                         ` Ira Weiny
2019-08-24  0:18                           ` Dave Chinner
2019-08-20  0:05               ` John Hubbard
2019-08-20  1:20                 ` Dave Chinner
2019-08-20  3:09                   ` John Hubbard
2019-08-20  3:36                     ` Dave Chinner
2019-08-21 18:43                       ` John Hubbard
2019-08-21 19:09                         ` Ira Weiny

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