From: Dave Chinner <david@fromorbit.com>
To: ira.weiny@intel.com
Cc: linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Dan Williams <dan.j.williams@intel.com>,
Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 05/12] fs: remove unneeded IS_DAX() check
Date: Tue, 11 Feb 2020 16:34:01 +1100 [thread overview]
Message-ID: <20200211053401.GE10776@dread.disaster.area> (raw)
In-Reply-To: <20200208193445.27421-6-ira.weiny@intel.com>
On Sat, Feb 08, 2020 at 11:34:38AM -0800, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> The IS_DAX() check in io_is_direct() causes a race between changing the
> DAX state and creating the iocb flags.
>
> Remove the check because DAX now emulates the page cache API and
> therefore it does not matter if the file state is DAX or not when the
> iocb flags are created.
This statement is ... weird.
DAX doesn't "emulate" the page cache API at all - it has it's own
read/write methods that filesystems call based on the iomap
infrastructure (dax_iomap_rw()). i.e. there are 3 different IO paths
through the filesystems: the DAX IO path, the direct IO path, and
the buffered IO path.
Indeed, it seems like this works a bit by luck: Ext4 and XFS always
check IS_DAX(inode) in the read/write_iter methods before checking
for IOCB_DIRECT, and hence the IOCB_DIRECT flag is ignored by the
filesystems. i.e. when we got rid of the O_DIRECT paths from DAX, we
forgot to clean up io_is_direct() and it's only due to the ordering
of checks that we went down the DAX path correctly....
That said, the code change is good, but the commit message needs a
rewrite.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-02-11 5:34 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-08 19:34 [PATCH v3 00/12] Enable per-file/directory DAX operations V3 ira.weiny
2020-02-08 19:34 ` [PATCH v3 01/12] fs/stat: Define DAX statx attribute ira.weiny
2020-02-08 19:34 ` [PATCH v3 02/12] fs/xfs: Isolate the physical DAX flag from effective ira.weiny
2020-02-08 19:34 ` [PATCH v3 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax() ira.weiny
2020-02-11 5:47 ` Dave Chinner
2020-02-11 16:13 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 04/12] fs/xfs: Clean up DAX support check ira.weiny
2020-02-11 5:57 ` Dave Chinner
2020-02-11 16:28 ` Ira Weiny
2020-02-11 20:38 ` Dave Chinner
2020-02-08 19:34 ` [PATCH v3 05/12] fs: remove unneeded IS_DAX() check ira.weiny
2020-02-11 5:34 ` Dave Chinner [this message]
2020-02-11 16:38 ` Ira Weiny
2020-02-11 20:41 ` Dave Chinner
2020-02-12 16:04 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under lock ira.weiny
2020-02-11 6:16 ` Dave Chinner
2020-02-11 17:55 ` Ira Weiny
2020-02-11 20:42 ` Dave Chinner
2020-02-12 16:10 ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 07/12] fs: Add locking for a dynamic DAX state ira.weiny
2020-02-11 8:00 ` Dave Chinner
2020-02-11 20:14 ` Ira Weiny
2020-02-11 20:59 ` Dan Williams
2020-02-11 21:49 ` Dave Chinner
2020-02-12 6:31 ` Darrick J. Wong
2020-02-11 17:51 ` kbuild test robot
2020-02-08 19:34 ` [PATCH v3 08/12] fs/xfs: Clarify lockdep dependency for xfs_isilocked() ira.weiny
2020-02-08 19:34 ` [PATCH v3 09/12] fs/xfs: Add write DAX lock to xfs layer ira.weiny
2020-02-08 19:34 ` [PATCH v3 10/12] fs: Prevent DAX state change if file is mmap'ed ira.weiny
2020-02-08 19:34 ` [PATCH v3 11/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-02-08 19:34 ` [PATCH v3 12/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny
2020-02-10 15:15 ` [PATCH v3 00/12] Enable per-file/directory DAX operations V3 Jeff Moyer
2020-02-11 20:17 ` Ira Weiny
2020-02-12 19:49 ` Jeff Moyer
2020-02-13 19:01 ` Ira Weiny
2020-02-13 19:05 ` Ira Weiny
2020-02-13 19:58 ` Darrick J. Wong
2020-02-13 23:29 ` Ira Weiny
2020-02-14 0:16 ` Dan Williams
2020-02-14 20:06 ` Ira Weiny
2020-02-14 21:23 ` Jeff Moyer
2020-02-14 21:58 ` Ira Weiny
2020-02-14 22:06 ` Jeff Moyer
2020-02-14 22:58 ` Jeff Moyer
2020-02-14 23:03 ` Jeff Moyer
2020-02-18 2:35 ` Ira Weiny
2020-02-18 14:22 ` Jeff Moyer
2020-02-18 23:54 ` Ira Weiny
2020-02-20 16:20 ` Ira Weiny
2020-02-20 16:30 ` Darrick J. Wong
2020-02-20 16:49 ` Ira Weiny
2020-02-20 17:00 ` Darrick J. Wong
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