From: Jan Kara <jack@suse.cz>
To: Jeff Layton <jlayton@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org,
bfields@fieldses.org, neilb@suse.de, jack@suse.de,
linux-ext4@vger.kernel.org, tytso@mit.edu,
adilger.kernel@dilger.ca, linux-xfs@vger.kernel.org,
darrick.wong@oracle.com, david@fromorbit.com,
linux-btrfs@vger.kernel.org, clm@fb.com, jbacik@fb.com,
dsterba@suse.com, linux-integrity@vger.kernel.org,
zohar@linux.vnet.ibm.com, dmitry.kasatkin@gmail.com,
linux-afs@lists.infradead.org, dhowells@redhat.com,
jaltman@auristor.com, krzk@kernel.org
Subject: Re: [PATCH v5 02/19] fs: don't take the i_lock in inode_inc_iversion
Date: Tue, 9 Jan 2018 16:14:28 +0100 [thread overview]
Message-ID: <20180109151428.yuhawmbgv7tywjcq@quack2.suse.cz> (raw)
In-Reply-To: <20180109141059.25929-3-jlayton@kernel.org>
On Tue 09-01-18 09:10:42, Jeff Layton wrote:
> From: Jeff Layton <jlayton@redhat.com>
>
> The rationale for taking the i_lock when incrementing this value is
> lost in antiquity. The readers of the field don't take it (at least
> not universally), so my assumption is that it was only done here to
> serialize incrementors.
>
> If that is indeed the case, then we can drop the i_lock from this
> codepath and treat it as a atomic64_t for the purposes of
> incrementing it. This allows us to use inode_inc_iversion without
> any danger of lock inversion.
>
> Note that the read side is not fetched atomically with this change.
> The assumption here is that that is not a critical issue since the
> i_version is not fully synchronized with anything else anyway.
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
This changes the memory barrier behavior but IMO it is good enough for an
intermediate version. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> include/linux/iversion.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> index d09cc3a08740..5ad9eaa3a9b0 100644
> --- a/include/linux/iversion.h
> +++ b/include/linux/iversion.h
> @@ -104,12 +104,13 @@ inode_set_iversion_queried(struct inode *inode, u64 new)
> static inline bool
> inode_maybe_inc_iversion(struct inode *inode, bool force)
> {
> - spin_lock(&inode->i_lock);
> - inode->i_version++;
> - spin_unlock(&inode->i_lock);
> + atomic64_t *ivp = (atomic64_t *)&inode->i_version;
> +
> + atomic64_inc(ivp);
> return true;
> }
>
> +
> /**
> * inode_inc_iversion - forcibly increment i_version
> * @inode: inode that needs to be updated
> --
> 2.14.3
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2018-01-09 15:14 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-09 14:10 [PATCH v5 00/19] fs: rework and optimize i_version handling in filesystems Jeff Layton
2018-01-09 14:10 ` [PATCH v5 01/19] fs: new API for handling inode->i_version Jeff Layton
2018-01-18 21:38 ` J. Bruce Fields
2018-01-18 22:47 ` Jeff Layton
2018-01-09 14:10 ` [PATCH v5 02/19] fs: don't take the i_lock in inode_inc_iversion Jeff Layton
2018-01-09 15:14 ` Jan Kara [this message]
2018-01-18 21:45 ` J. Bruce Fields
2018-01-19 14:36 ` Jeff Layton
2018-01-19 14:43 ` J. Bruce Fields
2018-01-09 14:10 ` [PATCH v5 03/19] fat: convert to new i_version API Jeff Layton
2018-01-09 14:10 ` [PATCH v5 04/19] affs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 05/19] afs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 06/19] btrfs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 07/19] exofs: switch " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 08/19] ext2: convert " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 09/19] ext4: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 10/19] nfs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 11/19] nfsd: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 12/19] ocfs2: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 13/19] ufs: use " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 14/19] xfs: convert to " Jeff Layton
2018-01-09 22:46 ` Dave Chinner
2018-01-09 14:10 ` [PATCH v5 15/19] IMA: switch IMA over " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 16/19] fs: only set S_VERSION when updating times if necessary Jeff Layton
2018-01-09 14:10 ` [PATCH v5 17/19] xfs: avoid setting XFS_ILOG_CORE if i_version doesn't need incrementing Jeff Layton
2018-01-09 22:48 ` Dave Chinner
2018-01-09 14:10 ` [PATCH v5 18/19] btrfs: only dirty the inode in btrfs_update_time if something was changed Jeff Layton
2018-01-11 19:30 ` Liu Bo
2018-01-09 14:10 ` [PATCH v5 19/19] fs: handle inode->i_version more efficiently Jeff Layton
2018-01-09 22:55 ` Dave Chinner
2018-01-10 14:12 ` Krzysztof Kozlowski
2018-01-11 20:23 ` [PATCH v5 00/19] fs: rework and optimize i_version handling in filesystems Liu Bo
2018-01-12 11:49 ` Jeff Layton
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