linux-kernel - Re: [patch 3/6] vfs: mountinfo stable peer group id

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Message-Id: <E1Jcd3y-0000gA-Nh@pomaz-ex.szeredi.hu>
Date:	Fri, 21 Mar 2008 09:57:22 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
CC:	miklos@...redi.hu, akpm@...ux-foundation.org, linuxram@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Trond.Myklebust@...app.com, dhowells@...hat.com
Subject: Re: [patch 3/6] vfs: mountinfo stable peer group id

> IOW, mark_mounts_for_expiry() should do the following:
> 	grabbing namespace_sem exclusive
> 	grab vfsmount_lock
> 	walk the list as it does now, except that it should do the right
> check from the very beginning (propagate_mount_busy())
> 	without dropping the vfsmount_lock, go through the collected list,
> calling umount_tree()
> 	drop the locks
> 	do release_mounts()
> The second pass is needed since umount_tree() might do interesting things
> to expiry list, so we make life easier for ourselves by leaving that to
> second pass when we just want to drain the resulting list until it's empty.
> 
> Does anybody see holes in the above?
> 
> shrink_submounts() is _probably_ similar (lock/collect/umount_tree on all/
> unlock/release_mounts), but I'm not sure if I understand WTF is really
> attempted in there.
> 
> Is there any reason why we do that in ->umount_begin() and not *after*
> it, unconditionally, straight from do_umount()?  AFAICS, the only reason
> why it's done from fs-specific code is figuring out which mount-list
> should the stuff go back to, and that's both broken *and* not needed
> with sanitized locking as above.  While we are at it, I'd rather return
> ->umount_begin() to its previous prototype, TYVM - the less filesystem
> sees vfsmounts, the better off we all are...

All of that seems sane to me.

Miklos
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