Re: [PATCH 1/2] mm: fix missing handler for __GFP_NOWARN

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On 2022/5/11 2:59 AM, Andrew Morton wrote:
On Tue, 10 May 2022 19:38:08 +0800 Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:

We expect no warnings to be issued when we specify __GFP_NOWARN, but
currently in paths like alloc_pages() and kmalloc(), there are still
some warnings printed, fix it.

Looks sane to me.

--- 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?


@@ -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@xxxxxxxxxxxxxxxxxxxxx)
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.

Thanks,
Qi

--
Thanks,
Qi




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