linux-ext4 - Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from deactivate_locked

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Message-Id: <20120608172842.9826b5cd.akpm@linux-foundation.org>
Date:	Fri, 8 Jun 2012 17:28:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Tao Ma <boyu.mt@...bao.com>, Nick Piggin <npiggin@...nel.dk>,
	"Dmitry V. Levin" <ldv@...linux.org>,
	v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org,
	linux-btrfs@...r.kernel.org, ceph-devel@...r.kernel.org,
	linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
	codalist@...emann.coda.cs.cmu.edu, ecryptfs@...r.kernel.org,
	osd-dev@...n-osd.org, linux-ext4@...r.kernel.org,
	fuse-devel@...ts.sourceforge.net, linux-mtd@...ts.infradead.org,
	jfs-discussion@...ts.sourceforge.net, logfs@...fs.org,
	linux-nfs@...r.kernel.org, linux-nilfs@...r.kernel.org,
	linux-ntfs-dev@...ts.sourceforge.net, ocfs2-devel@....oracle.com,
	reiserfs-devel@...r.kernel.org
Subject: Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from
 deactivate_locked_super() to filesystems

On Fri, 8 Jun 2012 16:46:47 -0700 Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Of course, if you just mean having a VFS wrapper that does
> 
>     static void vfs_inode_kmem_cache_destroy(struct kmem_cache *cachep)
>     {
>         rcu_barrier();
>         kmem_cache_destroy(cachep);
>     }
> 
> then we could do that. Not much better than what Kirill's patch did,
> but at least we could have that comment in just one single place.

That's conceptually what I meant.  But it has the problem that new and
out-of-tree filesystems might forget to do it.  Which is why I suggest
adding a kmem_cache* argument to unregister_filesystem() for this.

It's a bit awkward, and the fs can pass in NULL if it knows what it's
doing.  But it's reliable.
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