Re: [PATCH] x86/xen: only unlock when USE_SPLIT_PTE_PTLOCKS is true

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.09.2020 08:48, Jason Yan wrote:
> When USE_SPLIT_PTE_PTLOCKS is false, xen_pte_lock() actually do nothing
> but returns NULL. So xen_pte_unlock() should not actually unlock.
> Otherwise a NULL pointer dereference will be triggered.
> 
> Fixes: 74260714c56d ("xen: lock pte pages while pinning/unpinning")

I neither see any breakage this commit introduces, nor any NULL
deref. Both calls to (or arrangements to call) xen_pte_unlock() are
guarded by a check of the pointer to be non-NULL. Therefore if
anything this is a cosmetic change, which the description should
express, and which should have no Fixes: tag. (I would guess the
intention back then was to avoid #ifdef-ary where possible, at the
expense of a little bit of dead code.)

Jan