Re: [PATCH] mm: page_alloc: document kmemleak's non-blockable __GFP_NOFAIL case

[Yang Shi]

On 7/24/19 7:48 PM, Andrew Morton wrote:
> On Sat, 13 Jul 2019 04:49:04 +0800 Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote:
>
> > When running ltp's oom test with kmemleak enabled, the below warning was
> > triggerred since kernel detects __GFP_NOFAIL & ~__GFP_DIRECT_RECLAIM is
> > passed in:
> >
> > ...
> >
> > The mempool_alloc_slab() clears __GFP_DIRECT_RECLAIM, kmemleak has
> > __GFP_NOFAIL set all the time due to commit
> > d9570ee3bd1d4f20ce63485f5ef05663866fe6c0 ("kmemleak: allow to coexist
> > with fault injection").
> >
> > The fault-injection would not try to fail slab or page allocation if
> > __GFP_NOFAIL is used and that commit tries to turn off fault injection
> > for kmemleak allocation.  Although __GFP_NOFAIL doesn't guarantee no
> > failure for all the cases (i.e. non-blockable allocation may fail), it
> > still makes sense to the most cases.  Kmemleak is also a debugging tool,
> > so it sounds not worth changing the behavior.
> >
> > It also meaks sense to keep the warning, so just document the special
> > case in the comment.
> >
> > ...
> >
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4531,8 +4531,14 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
> >   	 */
> >   	if (gfp_mask & __GFP_NOFAIL) {
> >   		/*
> > -		 * All existing users of the __GFP_NOFAIL are blockable, so warn
> > -		 * of any new users that actually require GFP_NOWAIT
> > +		 * The users of the __GFP_NOFAIL are expected be blockable,
> > +		 * and this is true for the most cases except for kmemleak.
> > +		 * The kmemleak pass in __GFP_NOFAIL to skip fault injection,
> > +		 * however kmemleak may allocate object at some non-blockable
> > +		 * context to trigger this warning.
> > +		 *
> > +		 * Keep this warning since it is still useful for the most
> > +		 * normal cases.
> >   		 */
> Comment has rather a lot of typos.  I'd normally fix them but I think
> I'll duck this patch until the kmemleak situation is addressed, so we
> can add a kmemleakless long-term comment, if desired.

Actually, this has been replaced by reverting the problematic commit. 
And, the patch has been in -mm tree. Please see: 
revert-kmemleak-allow-to-coexist-with-fault-injection.patch

I think we would like to have this merged in 5.3-rc1 or rc2?