From: "Darrick J. Wong" <djwong@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Shiyang Ruan <ruansy.fnst@fujitsu.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
Linux NVDIMM <nvdimm@lists.linux.dev>,
Linux MM <linux-mm@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
david <david@fromorbit.com>,
Christoph Hellwig <hch@infradead.org>,
Jane Chu <jane.chu@oracle.com>
Subject: Re: [PATCH v9 01/10] dax: Use percpu rwsem for dax_{read,write}_lock()
Date: Wed, 5 Jan 2022 09:45:17 -0800 [thread overview]
Message-ID: <20220105174517.GI31606@magnolia> (raw)
In-Reply-To: <CAPcyv4gkxuFRGh57nYrpS8mXo+5j-7=KGNn-gULgLGthZQPo2g@mail.gmail.com>
On Tue, Jan 04, 2022 at 02:44:08PM -0800, Dan Williams wrote:
> On Sun, Dec 26, 2021 at 6:35 AM Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote:
> >
> > In order to introduce dax holder registration, we need a write lock for
> > dax.
>
> As far as I can see, no, a write lock is not needed while the holder
> is being registered.
>
> The synchronization that is needed is to make sure that the device
> stays live over the registration event, and that any in-flight holder
> operations are flushed before the device transitions from live to
> dead, and that in turn relates to the live state of the pgmap.
>
> The dax device cannot switch from live to dead without first flushing
> all readers, so holding dax_read_lock() over the register holder event
> should be sufficient.
...and perhaps add a comment describing that this is what the
synchronization primitive is really protecting against? The first time
I read through this patchset, I assumed the rwsem was protecting
&dax_hosts and was confused when I saw the one use of dax_write_lock.
--D
> If you are worried about 2 or more potential
> holders colliding at registration time, I would expect that's already
> prevented by block device exclusive holder synchronization, but you
> could also use cmpxchg and a single pointer to a 'struct dax_holder {
> void *holder_data, struct dax_holder_operations *holder_ops }'. If you
> are worried about memory_failure triggering while the filesystem is
> shutting down it can do a synchronize_srcu(&dax_srcu) if it really
> needs to ensure that the notify path is idle after removing the holder
> registration.
>
> ...are there any cases remaining not covered by the above suggestions?
next prev parent reply other threads:[~2022-01-05 17:45 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-26 14:34 [PATCH v9 00/10] fsdax: introduce fs query to support reflink Shiyang Ruan
2021-12-26 14:34 ` [PATCH v9 01/10] dax: Use percpu rwsem for dax_{read,write}_lock() Shiyang Ruan
2022-01-04 22:44 ` Dan Williams
2022-01-05 17:45 ` Darrick J. Wong [this message]
2022-01-06 11:06 ` Shiyang Ruan
2021-12-26 14:34 ` [PATCH v9 02/10] dax: Introduce holder for dax_device Shiyang Ruan
2022-01-05 18:12 ` Darrick J. Wong
2022-01-05 18:23 ` Dan Williams
2022-01-05 18:56 ` Darrick J. Wong
2022-01-05 19:20 ` Dan Williams
2022-01-05 22:47 ` Darrick J. Wong
2022-01-05 23:01 ` Dan Williams
2022-01-05 23:54 ` Darrick J. Wong
2022-01-06 0:12 ` Dan Williams
2022-01-20 8:46 ` Christoph Hellwig
2022-01-21 1:26 ` Shiyang Ruan
2022-01-21 2:22 ` Darrick J. Wong
2022-01-21 7:17 ` Christoph Hellwig
2022-02-15 21:51 ` Dan Williams
2021-12-26 14:34 ` [PATCH v9 03/10] mm: factor helpers for memory_failure_dev_pagemap Shiyang Ruan
2021-12-26 14:34 ` [PATCH v9 04/10] pagemap,pmem: Introduce ->memory_failure() Shiyang Ruan
2022-01-05 19:06 ` Darrick J. Wong
2021-12-26 14:34 ` [PATCH v9 05/10] fsdax: fix function description Shiyang Ruan
2022-01-05 17:50 ` Darrick J. Wong
2022-01-20 8:47 ` Christoph Hellwig
2021-12-26 14:34 ` [PATCH v9 06/10] fsdax: Introduce dax_lock_mapping_entry() Shiyang Ruan
2022-01-04 22:55 ` Dan Williams
2021-12-26 14:34 ` [PATCH v9 07/10] mm: move pgoff_address() to vma_pgoff_address() Shiyang Ruan
2022-01-20 8:47 ` Christoph Hellwig
2021-12-26 14:34 ` [PATCH v9 08/10] mm: Introduce mf_dax_kill_procs() for fsdax case Shiyang Ruan
2022-01-20 8:55 ` Christoph Hellwig
2021-12-26 14:34 ` [PATCH v9 09/10] xfs: Implement ->notify_failure() for XFS Shiyang Ruan
2022-01-05 18:53 ` Darrick J. Wong
2022-01-05 21:17 ` Dan Williams
2021-12-26 14:34 ` [PATCH v9 10/10] fsdax: set a CoW flag when associate reflink mappings Shiyang Ruan
2022-01-20 8:59 ` Christoph Hellwig
2022-01-21 2:33 ` Shiyang Ruan
2022-01-21 7:16 ` Christoph Hellwig
2022-01-21 8:34 ` Shiyang Ruan
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