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

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Message-ID: <4FD2F5F4.1000106@gmail.com>
Date:	Sat, 09 Jun 2012 09:06:28 +0200
From:	Marco Stornelli <marco.stornelli@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"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

Il 09/06/2012 02:28, Andrew Morton ha scritto:
> 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.
> --

The call of rcu_barrier should be mandatory for the "unload fs module" 
problem, right? If the fs is compiled statically maybe we could avoid 
it, but (eventually) this kind of decision is per-fs, so this could be a 
clue that the call of rcu_barrier maybe is inside each fs not in VFS.

Marco
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