Re: [PATCH v2] xfs: zero newly allocated btree root space

[Carlos Maiolino <cem@kernel.org>]

On Thu, Jul 02, 2026 at 08:31:02AM -0700, Darrick J. Wong wrote:
> On Thu, Jul 02, 2026 at 04:05:06AM -0700, Christoph Hellwig wrote:
> > On Wed, Jul 01, 2026 at 08:52:34AM -0700, Darrick J. Wong wrote:
> > > > This almost sounds like we should explicitly zero this case just for that
> > > > particular case.  Although Darrick was kinda heading in a different
> > > > direction and I don't want to start a fight here.
> > > 
> > > I'm fine with either solution; I simply prefer the one that fixes all
> > > the current and future "oops we forgot to zero a hidden padding" bugs in
> > > one action.
> > 
> > Maybe we should avoid creating hidden zero padding to start with? :)
> > But this is a small allocation, and most of it gets overwritten
> > while the cache is still hot, so I can live with the unconditional
> > zeroing.  Still feels a bit odd to reach for the big hammer.
> 
> <shrug> If this is truly the only place where we forget to initialize
> if_broot fully then I'm ok with just doing that and not going for
> GFP_ZERO.  If we have an army of KASAN syzbotters whacking away at the
> system, then I could reevaluate my resistance to whack-a-mole.
> 
> --D
> 

Sorry, this conversation fell through the cracks.

I'd say the right approach here would be to measure the performance
penalty if we opt to go with GFP_ZERO and document it on the patch
description.
But I'd also prefer to just closing this gap and initializing if_broot
only here instead of GFP_ZEROing everything.