Commit 7594c461 authored Dec 18, 2017 by Jeff Layton

fs: don't take the i_lock in inode_inc_iversion



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>
Reviewed-by: Jan Kara <jack@suse.cz>

parent ae5e165d

include/linux/iversion.h

+4 −3

Original line number	Diff line number	Diff line
		@@ -110,12 +110,13 @@ 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

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