mm/page_alloc: Revert pahole zero-sized workaround

Commit dbbee9d ("mm/page_alloc: convert per-cpu list protection to
local_lock") folded in a workaround patch for pahole that was unable to
deal with zero-sized percpu structures.

A superior workaround is achieved with commit a0b8200 ("kbuild:
skip per-CPU BTF generation for pahole v1.18-v1.21").

This patch reverts the dummy field and the pahole version check.

Fixes: dbbee9d ("mm/page_alloc: convert per-cpu list protection to local_lock")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: gormanm

lib/Kconfig.debug

@@ -324,9 +324,6 @@ config DEBUG_INFO_BTF
 config PAHOLE_HAS_SPLIT_BTF
 	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
 
-config PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT
-	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "122")
-
 config DEBUG_INFO_BTF_MODULES
 	def_bool y
 	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF

mm/page_alloc.c

@@ -124,17 +124,6 @@ static DEFINE_MUTEX(pcp_batch_high_lock);
 
 struct pagesets {
 	local_lock_t lock;
-#if defined(CONFIG_DEBUG_INFO_BTF) &&				\
-	!defined(CONFIG_DEBUG_LOCK_ALLOC) &&			\
-	!defined(CONFIG_PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT)
-	/*
-	 * pahole 1.21 and earlier gets confused by zero-sized per-CPU
-	 * variables and produces invalid BTF. Ensure that
-	 * sizeof(struct pagesets) != 0 for older versions of pahole.
-	 */
-	char __pahole_hack;
-	#warning "pahole too old to support zero-sized struct pagesets"
-#endif
 };
 static DEFINE_PER_CPU(struct pagesets, pagesets) = {
 	.lock = INIT_LOCAL_LOCK(lock),