linux-kernel - Re: [PATCH 2/3] vfs: add propagate_mount_tree

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Message-ID: <41252c7e-674b-c110-962b-c20204dc7424@themaw.net>
Date:   Wed, 20 Jul 2022 10:31:26 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] vfs: add propagate_mount_tree_busy() helper


On 20/7/22 09:54, Al Viro wrote:
> On Mon, Jul 11, 2022 at 11:37:46AM +0800, Ian Kent wrote:
>
>> +static int do_mount_in_use_check(struct mount *mnt, int cnt)
>> +{
>> +	struct mount *topper;
>> +
>> +	/* Is there exactly one mount on the child that covers
>> +	 * it completely?
>> +	 */
>> +	topper = find_topper(mnt);
>> +	if (topper) {
>> +		int topper_cnt = topper->mnt_mounts_cnt + 1;
>> +
>> +		/* Open file or pwd within singular mount? */
>> +		if (do_refcount_check(topper, topper_cnt))
>> +			return 1;
> Whatever the hell for?  umount(2) will be able to slide the
> underlying mount from under the topper, whatever the
> refcount of topper might have been.

My thinking was that a process could have set a working

directory (or opened a descriptor) and some later change

to an autofs map resulted in it being mounted on. It's

irrelevant now with your suggested simpler approach, ;)


Ian