Re: [PATCH] Shift BKL into ->statfs()

[Alexander Viro]

On Wed, 3 Jul 2002, Matthew Wilcox wrote:

> On Tue, Jul 02, 2002 at 06:25:47PM -0700, Paul Menage wrote:
> > This patch removes BKL protection from the invocation of the
> > super_operations ->statfs() method, and shifts it into the filesystems
> > where necessary. Any out-of-tree filesystems may need to take the BKL in
> > their statfs() methods if they were relying on it for synchronisation.
> 
> Sure, makes sense to do.  For real credit though, let's see how much we
> need the BKL.  In ext2's statfs, we reference:

[snip]

> s_mount_opt doesn't actually need to be locked due to how it is
> modified & used.  So it _looks_ like we only need to lock_super(sb); /
> unlock_super(sb); in ext2.  Anyone more familiar with ext2 locking care
> to comment?

We actually don't need even that - the only places that might need
lock_super() (ext2_count_free_blocks()/ext2_count_free_inodes()) are
already taking it.

So BKL can be dropped in ext2_statfs() and no extra locks are needed.

> I bet most other filesystems can handle lock_super / unlock_super
> for themselves.  See if some kerneljanitors are willing to help audit,
> perhaps?

Depending on filesystem, lock_super() might be a bad idea.  Keep in
mind that these days ->s_lock is a private filesystem lock...