On Sun, Oct 03, 2021 at 06:07:20PM -0700, David Rientjes wrote:

On Thu, 30 Sep 2021, Rustam Kovhaev wrote:

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I think it's fair if something like XFS (not meant for tiny systems AFAIK?)
excludes SLOB (meant for tiny systems). Clearly nobody tried to use these
two together last 5 years anyway.

+1 for adding Kconfig option, it seems like some things are not meant to
be together.

But if we patch SLOB, we won't need it.

OK, so we consider XFS on SLOB a supported configuration that might be
used and should be tested.
I'll look into maybe adding a config with CONFIG_SLOB and CONFIG_XFS_FS
to syzbot.

It seems that we need to patch SLOB anyway, because any other code can
hit the very same issue.

It's probably best to introduce both (SLOB fix and Kconfig change for 
XFS), at least in the interim because the combo of XFS and SLOB could be 
broken in other ways.  If syzbot doesn't complain with a patched kernel to 
allow SLOB to be used with XFS, then we could potentially allow them to be 
used together.

(I'm not sure that this freeing issue is the *only* thing that is broken, 
nor that we have sufficient information to make that determination right 
now..)

I audited the entire xfs (kernel) codebase and didn't find any other
usage errors.  Thanks for the patch; I'll apply it to for-next.

--D