linux-kernel - Re: [PATCH -V2 12/13] fsnotify: handle filesystem unmounts with fsnotify marks

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Message-Id: <20090407160635.236772e5.akpm@linux-foundation.org>
Date:	Tue, 7 Apr 2009 16:06:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	hch@...radead.org, alan@...rguk.ukuu.org.uk, sfr@...b.auug.org.au,
	john@...nmccutchan.com, rlove@...ve.org
Subject: Re: [PATCH -V2 12/13] fsnotify: handle filesystem unmounts with
 fsnotify marks

On Fri, 27 Mar 2009 16:06:11 -0400
Eric Paris <eparis@...hat.com> wrote:

> When an fs is unmounted with an fsnotify mark entry attached to one of its
> inodes we need to destroy that mark entry and we also (like inotify) send
> an unmount event.
> 
>
> ...
>
> +/**
> + * fsnotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
> + * @list: list of inodes being unmounted (sb->s_inodes)
> + *
> + * Called with inode_lock held, protecting the unmounting super block's list
> + * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
> + * We temporarily drop inode_lock, however, and CAN block.
> + */
> +void fsnotify_unmount_inodes(struct list_head *list)
> +{
> +	struct inode *inode, *next_i, *need_iput = NULL;
> +
> +	list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
> +		struct inode *need_iput_tmp;
> +
> +		/*
> +		 * If i_count is zero, the inode cannot have any watches and
> +		 * doing an __iget/iput with MS_ACTIVE clear would actually
> +		 * evict all inodes with zero i_count from icache which is
> +		 * unnecessarily violent and may in fact be illegal to do.
> +		 */
> +		if (!atomic_read(&inode->i_count))
> +			continue;
> +
> +		/*
> +		 * We cannot __iget() an inode in state I_CLEAR, I_FREEING, or
> +		 * I_WILL_FREE which is fine because by that point the inode
> +		 * cannot have any associated watches.
> +		 */
> +		if (inode->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))
> +			continue;
> +
> +		need_iput_tmp = need_iput;
> +		need_iput = NULL;
> +
> +		/* In case fsnotify_inode_delete() drops a reference. */
> +		if (inode != need_iput_tmp)
> +			__iget(inode);
> +		else
> +			need_iput_tmp = NULL;
> +
> +		/* In case the dropping of a reference would nuke next_i. */
> +		if ((&next_i->i_sb_list != list) &&
> +		    atomic_read(&next_i->i_count) &&
> +		    !(next_i->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))) {
> +			__iget(next_i);
> +			need_iput = next_i;
> +		}
> +
> +		/*
> +		 * We can safely drop inode_lock here because we hold
> +		 * references on both inode and next_i.  Also no new inodes
> +		 * will be added since the umount has begun.  Finally,
> +		 * iprune_mutex keeps shrink_icache_memory() away.
> +		 */
> +		spin_unlock(&inode_lock);
> +
> +		if (need_iput_tmp)
> +			iput(need_iput_tmp);

iput(NULL) is legal.

> +		/* for each watch, send FS_UNMOUNT and then remove it */
> +		fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0);
> +
> +		fsnotify_inode_delete(inode);
> +
> +		iput(inode);
> +
> +		spin_lock(&inode_lock);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(fsnotify_unmount_inodes);

Why is it exported?
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