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

[Marco Stornelli <marco.stornelli@gmail.com>]

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