Re: [2/4] powerpc/mm: Handle removing maybe-present bolted HPTEs

[Michael Ellerman]

On Tue, 2016-09-02 at 03:32:41 UTC, David Gibson wrote:
> At the moment the hpte_removebolted callback in ppc_md returns void and
> will BUG_ON() if the hpte it's asked to remove doesn't exist in the first
> place.  This is awkward for the case of cleaning up a mapping which was
> partially made before failing.
> 
> So, we add a return value to hpte_removebolted, and have it return ENOENT
> in the case that the HPTE to remove didn't exist in the first place.
> 
> In the (sole) caller, we propagate errors in hpte_removebolted to its
> caller to handle.  However, we handle ENOENT specially, continuing to
> complete the unmapping over the specified range before returning the error
> to the caller.
> 
> This means that htab_remove_mapping() will work sanely on a partially
> present mapping, removing any HPTEs which are present, while also returning
> ENOENT to its caller in case it's important there.
> 
> There are two callers of htab_remove_mapping():
>    - In remove_section_mapping() we already WARN_ON() any error return,
>      which is reasonable - in this case the mapping should be fully
>      present
>    - In vmemmap_remove_mapping() we BUG_ON() any error.  We change that to
>      just a WARN_ON() in the case of ENOENT, since failing to remove a
>      mapping that wasn't there in the first place probably shouldn't be
>      fatal.
> 
> Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/27828f98a0522ad4a745a80407

cheers