Re: [PATCH] mm: Use local variable for swap address space

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 19 Jun 2019, "Summers, Stuart" <stuart.summers@intel.com> wrote:
> On Wed, 2019-06-19 at 18:30 +0300, Jani Nikula wrote:
>> On Tue, 18 Jun 2019, Stuart Summers <stuart.summers@intel.com> wrote:
>> > This addresses the following build error:
>> > mm/huge_memory.c: In function ‘__split_huge_page’:
>> > mm/huge_memory.c:2506:41: warning: dereferencing ‘void *’ pointer
>> >     __xa_store(&swap_address_space(entry)->i_pages,
>> >                                          ^~
>> > mm/huge_memory.c:2506:41: error: request for member ‘i_pages’ in
>> > something not a structure or union
>> 
>> Did you check under what circumstances it would be a void pointer?
>
> This got things working, but I agree probably needs at least some basic
> checks here. I'll rework it.

Hint: CONFIG_SWAP.

BR,
Jani.


>
>> 
>> Under those circumstances, what do you think will happen runtime
>> after
>> you've brushed the build error under the carpet?
>> 
>> Anyway, the patch is against a commit in topic/core-for-CI, not to be
>> merged elsewhere.
>
> Ok thanks for the feedback and makes sense. I'll resubmit.
>
> Thanks,
> Stuart
>
>> 
>> BR,
>> Jani.
>> 
>> 
>> 
>> > 
>> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> > Signed-off-by: Stuart Summers <stuart.summers@intel.com>
>> > ---
>> >  mm/huge_memory.c | 4 +++-
>> >  1 file changed, 3 insertions(+), 1 deletion(-)
>> > 
>> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> > index affb2c3667f9..bced5485137b 100644
>> > --- a/mm/huge_memory.c
>> > +++ b/mm/huge_memory.c
>> > @@ -2503,7 +2503,9 @@ static void __split_huge_page(struct page
>> > *page, struct list_head *list,
>> >  					head + i, 0);
>> >  		} else if (PageSwapCache(page)) {
>> >  			swp_entry_t entry = { .val = page_private(head
>> > + i) };
>> > -			__xa_store(&swap_address_space(entry)->i_pages,
>> > +			struct address_space *address_space =
>> > +				swap_address_space(entry);
>> > +			__xa_store(&address_space->i_pages,
>> >  				   swp_offset(entry),
>> >  				   head + i, 0);
>> >  		}
>> 
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center
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