linux-kernel - Re: The bug of iput() removal from flusher thread?

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Message-Id: <20121121000533.a0ab9eea.akpm@linux-foundation.org>
Date:	Wed, 21 Nov 2012 00:05:33 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: The bug of iput() removal from flusher thread?

On Wed, 21 Nov 2012 02:48:51 +0100 Jan Kara <jack@...e.cz> wrote:

> +/*
> + * Add inode to LRU if needed (inode is unused and clean).
> + *
> + * Needs inode->i_lock held.
> + */
> +void inode_add_lru(struct inode *inode)
> +{
> +	if (!(inode->i_state & (I_DIRTY | I_FREEING | I_SYNC)) &&
> +	    !atomic_read(&inode->i_count) && inode->i_sb->s_flags & MS_ACTIVE)
> +		inode_lru_list_add(inode);
> +}

Is i_lock sufficient to stabilise i_count?

<looks at the code a bit>

Is evict_inodes() wrong to test i_count outside i_lock?

invalidate_inodes() looks better.

can_unuse() must be called under i_lock, and is.  Apparently this
requirement was sufficiently obvious to not meed documenting.

prune_icache_sb() gets it right.

iput() gets it right.

So to answer my own question: yes, it is sufficient.  But a) the
comment for inode.i_lock is out of date and b) evict_inodes() looks
fishy.

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