Re: [PATCH 05/43] xfs: don't take m_sb_lock in xfs_fs_statfs

Darrick J. Wong
2024-12-15T18:16:09Z

On Fri, Dec 13, 2024 at 06:06:15AM +0100, Christoph Hellwig wrote:
> On Thu, Dec 12, 2024 at 01:42:06PM -0800, Darrick J. Wong wrote:
> > On Wed, Dec 11, 2024 at 09:54:30AM +0100, Christoph Hellwig wrote:
> > > The only non-constant value read under m_sb_lock in xfs_fs_statfs is
> > > sb_dblocks, and it could become stale right after dropping the lock
> > > anyway. Remove the thus pointless lock section.
> >
> > Is there a stronger reason later for removing the critical section?
> > Do we lose much by leaving the protection in place?
>
> It makes a completely mess of xfs_fs_statfs, and as stated in the
> commit message about it's not actually useful at all. I also don't
> think taking a global lock from a non-privileged operation is an
> old that good idea to start with if we can avoid it.

Ok, I'm convinced. But perhaps you could leave a comment that we don't
care if the accesses are torn, to try to head off the inevitable kcsan/
dept/whatever patches?

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D