Commit 59b5ed40 authored by Hao Ge's avatar Hao Ge Committed by Andrew Morton
Browse files

mm/percpu: conditionally define _shared_alloc_tag via CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU 

Recently discovered this entry while checking kallsyms on ARM64:
ffff800083e509c0 D _shared_alloc_tag

If ARCH_NEEDS_WEAK_PER_CPU is not defined(it is only defined for s390 and
alpha architectures), there's no need to statically define the percpu
variable _shared_alloc_tag.

Therefore, we need to implement isolation for this purpose.

When building the core kernel code for s390 or alpha architectures,
ARCH_NEEDS_WEAK_PER_CPU remains undefined (as it is gated by #if
defined(MODULE)).  However, when building modules for these architectures,
the macro is explicitly defined.

Therefore, we remove all instances of ARCH_NEEDS_WEAK_PER_CPU from the
code and introduced CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU to replace the
relevant logic.  We can now conditionally define the perpcu variable
_shared_alloc_tag based on CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU.  This
allows architectures (such as s390/alpha) that require weak definitions
for percpu variables in modules to include the definition, while others
can omit it via compile-time exclusion.

Link: https://lkml.kernel.org/r/20250618015809.1235761-1-hao.ge@linux.dev


Signed-off-by: default avatarHao Ge <gehao@kylinos.cn>
Suggested-by: default avatarSuren Baghdasaryan <surenb@google.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>	[s390]
Acked-by: default avatarMike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Chistoph Lameter <cl@linux.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent cf34cfbf

arch/alpha/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ config ALPHA 
	select ARCH_HAS_DMA_OPS if PCI

	select ARCH_MIGHT_HAVE_PC_PARPORT

	select ARCH_MIGHT_HAVE_PC_SERIO

	select ARCH_MODULE_NEEDS_WEAK_PER_CPU if SMP

	select ARCH_NO_PREEMPT

	select ARCH_NO_SG_CHAIN

	select ARCH_USE_CMPXCHG_LOCKREF

arch/alpha/include/asm/percpu.h

+2 −3
Original line number Diff line number Diff line
@@ -9,10 +9,9 @@ 
 * way above 4G.

 *

 * Always use weak definitions for percpu variables in modules.

 * Therefore, we have enabled CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU

 * in the Kconfig.

 */

#if defined(MODULE) && defined(CONFIG_SMP)

#define ARCH_NEEDS_WEAK_PER_CPU

#endif



#include <asm-generic/percpu.h>

arch/s390/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -132,6 +132,7 @@ config S390 
	select ARCH_INLINE_WRITE_UNLOCK_IRQ

	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE

	select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE

	select ARCH_MODULE_NEEDS_WEAK_PER_CPU

	select ARCH_STACKWALK

	select ARCH_SUPPORTS_ATOMIC_RMW

	select ARCH_SUPPORTS_DEBUG_PAGEALLOC

arch/s390/include/asm/percpu.h

+2 −3
Original line number Diff line number Diff line
@@ -16,10 +16,9 @@ 
 * For 64 bit module code, the module may be more than 4G above the

 * per cpu area, use weak definitions to force the compiler to

 * generate external references.

 * Therefore, we have enabled CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU

 * in the Kconfig.

 */

#if defined(MODULE)

#define ARCH_NEEDS_WEAK_PER_CPU

#endif



/*

 * We use a compare-and-swap loop since that uses less cpu cycles than

include/linux/alloc_tag.h

+3 −3
Original line number Diff line number Diff line
@@ -88,7 +88,7 @@ static inline struct alloc_tag *ct_to_alloc_tag(struct codetag *ct) 
	return container_of(ct, struct alloc_tag, ct);

}



#ifdef ARCH_NEEDS_WEAK_PER_CPU

#if defined(CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU) && defined(MODULE)

/*

 * When percpu variables are required to be defined as weak, static percpu

 * variables can't be used inside a function (see comments for DECLARE_PER_CPU_SECTION).
@@ -102,7 +102,7 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag); 
		.ct = CODE_TAG_INIT,						\

		.counters = &_shared_alloc_tag };



#else /* ARCH_NEEDS_WEAK_PER_CPU */

#else /* CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU && MODULE */



#ifdef MODULE
@@ -123,7 +123,7 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag); 


#endif /* MODULE */



#endif /* ARCH_NEEDS_WEAK_PER_CPU */

#endif /* CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU && MODULE */



DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,

			mem_alloc_profiling_key);