linux-kernel - Re: [PATCH 1/2] mm: fix missing handler for __GFP

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Date:   Tue, 10 May 2022 19:32:15 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     akinobu.mita@...il.com, vbabka@...e.cz, gregkh@...uxfoundation.org,
        jirislaby@...nel.org, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm: fix missing handler for __GFP_NOWARN

On Wed, 11 May 2022 10:19:48 +0800 Qi Zheng <zhengqi.arch@...edance.com> wrote:

> 
> ,,,
> >> --- a/mm/internal.h
> >> +++ b/mm/internal.h
> >> @@ -35,6 +35,17 @@ struct folio_batch;
> >>   /* Do not use these with a slab allocator */
> >>   #define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK)
> >>   
> >> +#define WARN_ON_ONCE_GFP(cond, gfp)	({				\
> >> +	static bool __section(".data.once") __warned;			\
> >> +	int __ret_warn_once = !!(cond);					\
> >> +									\
> >> +	if (unlikely(!(gfp & __GFP_NOWARN) && __ret_warn_once && !__warned)) { \
> >> +		__warned = true;					\
> >> +		WARN_ON(1);						\
> >> +	}								\
> >> +	unlikely(__ret_warn_once);					\
> >> +})
> > 
> > I don't think WARN_ON_ONCE_GFP is a good name for this.  But
> > WARN_ON_ONCE_IF_NOT_GFP_NOWARN is too long :(
> > 
> > WARN_ON_ONCE_NOWARN might be better.  No strong opinion here, really.
> 
> I've thought about WARN_ON_ONCE_NOWARN, but I feel a little weird 
> putting 'WARN' and 'NOWARN' together, how about WARN_ON_ONCE_IF_ALLOWED?

I dunno.  WARN_ON_ONCE_GFP isn't too bad I suppose.  Add a comment over
the definition explaining it?

> > 
> >> @@ -4902,8 +4906,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >>   	 * We also sanity check to catch abuse of atomic reserves being used by
> >>   	 * callers that are not in atomic context.
> >>   	 */
> >> -	if (WARN_ON_ONCE((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
> >> -				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
> >> +	if (WARN_ON_ONCE_GFP((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
> >> +				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM), gfp_mask))
> >>   		gfp_mask &= ~__GFP_ATOMIC;
> >>   
> >>   retry_cpuset:
> > 
> > I dropped this hunk - Neil's "mm: discard __GFP_ATOMIC"
> > (https://lkml.kernel.org/r/163712397076.13692.4727608274002939094@noble.neil.brown.name)
> > deleted this code.
> > 
> 
> This series is based on v5.18-rc5, I will rebase it to the latest next
> branch and check if there are any missing WARN_ON_ONCEs that are not
> being handled.

Against git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm branch
mm-unstable, please.  That ends up in linux-next, with a delay.