Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from deactivate_locked_super() to filesystems

Marco Stornelli
2012-06-09T07:13:13Z

Il 09/06/2012 02:28, Andrew Morton ha scritto:
> On Fri, 8 Jun 2012 16:46:47 -0700 Linus Torvalds<torvalds@linux-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