linux-kernel - Re: [PATCH] fs/inode: No need to take ->i_lock right after alloc

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Message-ID: <20140110092229.GA556@lst.de>
Date:	Fri, 10 Jan 2014 10:22:29 +0100
From:	Christoph Hellwig <hch@....de>
To:	Richard Weinberger <richard@....at>
Cc:	viro@...iv.linux.org.uk, dchinner@...hat.com, hch@....de,
	eric.dumazet@...il.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/inode: No need to take ->i_lock right after
	alloc_inode()

On Wed, Jan 08, 2014 at 11:21:13AM +0100, Richard Weinberger wrote:
> > In all three cases, new_inode_pseudo(), iget_locked() and iget5_locked(),
> > we own the new inode exclusively at this point and therefore taking
> > ->i_lock to protect ->i_state/->i_hash against concurrent access is
> > superfluous.

We'd still need some sort of barrier to make sure the state is visible
to all CPUs before it becomes visible, usually by another spin_unlock
happing later.  If you have a workload where removing these is critical
please document these issues in the code and resubmit it with an explanation
of the workload where it helps.  If it's just a cleanup I wouldn't bother
with it.

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