From a6773e6932cbfbc0e123bc0529ea27f2a8abb833 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Thu, 23 Oct 2025 10:38:50 -0700 Subject: [PATCH 1/7] jfs: Rename _inline to avoid conflict with clang's '-fms-extensions' Building fs/jfs with clang and '-fms-extensions' errors with: In file included from fs/jfs/jfs_unicode.c:8: fs/jfs/jfs_incore.h:86:13: error: type name does not allow function specifier to be specified 86 | unchar _inline[128]; | ^ fs/jfs/jfs_incore.h:86:20: error: expected member name or ';' after declaration specifiers 86 | unchar _inline[128]; | ~~~~~~~~~~~~~~^ '-fms-extensions' in clang enables several other Microsoft specific keywords such as _inline [1], presumably for compatibility with MSVC, as Microsoft's documentation [2] mentions: For compatibility with previous versions, _inline and _forceinline are synonyms for __inline and __forceinline, respectively Rename the _inline array in 'struct jfs_inode_info' to _inline_sym to avoid this conflict, which is not a large workaround as this member is only ever referred to via the i_inline macro. Link: https://github.com/llvm/llvm-project/blob/249883d0c5883996bed038cd82a8999f342994c9/clang/include/clang/Basic/TokenKinds.def#L744-L79 [1] Link: https://learn.microsoft.com/en-us/cpp/c-language/inline-functions [2] Acked-by: Dave Kleikamp Link: https://patch.msgid.link/20251023-jfs-fix-conflict-with-clang-ms-ext-v1-1-e219d59a1e68@kernel.org Signed-off-by: Nathan Chancellor --- fs/jfs/jfs_incore.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/jfs/jfs_incore.h b/fs/jfs/jfs_incore.h index 10934f9a11be..5aaafedb8fbc 100644 --- a/fs/jfs/jfs_incore.h +++ b/fs/jfs/jfs_incore.h @@ -76,14 +76,14 @@ struct jfs_inode_info { struct { unchar _unused[16]; /* 16: */ dxd_t _dxd; /* 16: */ - /* _inline may overflow into _inline_ea when needed */ + /* _inline_sym may overflow into _inline_ea when needed */ /* _inline_ea may overlay the last part of * file._xtroot if maxentry = XTROOTINITSLOT */ union { struct { /* 128: inline symlink */ - unchar _inline[128]; + unchar _inline_sym[128]; /* 128: inline extended attr */ unchar _inline_ea[128]; }; @@ -101,7 +101,7 @@ struct jfs_inode_info { #define i_imap u.file._imap #define i_dirtable u.dir._table #define i_dtroot u.dir._dtroot -#define i_inline u.link._inline +#define i_inline u.link._inline_sym #define i_inline_ea u.link._inline_ea #define i_inline_all u.link._inline_all From c4781dc3d1cf0e017e1f290607ddc56cfe187afc Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Mon, 20 Oct 2025 16:22:27 +0200 Subject: [PATCH 2/7] Kbuild: enable -fms-extensions Once in a while, it turns out that enabling -fms-extensions could allow some slightly prettier code. But every time it has come up, the code that had to be used instead has been deemed "not too awful" and not worth introducing another compiler flag for. That's probably true for each individual case, but then it's somewhat of a chicken/egg situation. If we just "bite the bullet" as Linus says and enable it once and for all, it is available whenever a use case turns up, and no individual case has to justify it. A lore.kernel.org search provides these examples: - https://lore.kernel.org/lkml/200706301813.58435.agruen@suse.de/ - https://lore.kernel.org/lkml/20180419152817.GD25406@bombadil.infradead.org/ - https://lore.kernel.org/lkml/170622208395.21664.2510213291504081000@noble.neil.brown.name/ - https://lore.kernel.org/lkml/87h6475w9q.fsf@prevas.dk/ - https://lore.kernel.org/lkml/CAHk-=wjeZwww6Zswn6F_iZTpUihTSNKYppLqj36iQDDhfntuEw@mail.gmail.com/ Undoubtedly, there are more places in the code where this could also be used but where -fms-extensions just didn't come up in any discussion. Signed-off-by: Rasmus Villemoes Acked-by: David Sterba Link: https://patch.msgid.link/20251020142228.1819871-2-linux@rasmusvillemoes.dk [nathan: Move disabled clang warning to scripts/Makefile.extrawarn and adjust comment] Signed-off-by: Nathan Chancellor --- Makefile | 3 +++ scripts/Makefile.extrawarn | 4 +++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/Makefile b/Makefile index 17cfa11ca716..1dc8873d4968 100644 --- a/Makefile +++ b/Makefile @@ -1061,6 +1061,9 @@ NOSTDINC_FLAGS += -nostdinc # perform bounds checking. KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3) +# Allow including a tagged struct or union anonymously in another struct/union. +KBUILD_CFLAGS += -fms-extensions + # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += -fno-strict-overflow diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 6af392f9cd02..68e6fafcb80c 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -28,8 +28,10 @@ endif KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds ifdef CONFIG_CC_IS_CLANG -# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. +# The kernel builds with '-std=gnu11' and '-fms-extensions' so use of GNU and +# Microsoft extensions is acceptable. KBUILD_CFLAGS += -Wno-gnu +KBUILD_CFLAGS += -Wno-microsoft-anon-tag # Clang checks for overflow/truncation with '%p', while GCC does not: # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 From 5ff8ad3909524ad55297a434f87c238224825bf4 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Thu, 30 Oct 2025 21:26:28 -0400 Subject: [PATCH 3/7] kbuild: Add '-fms-extensions' to areas with dedicated CFLAGS This is a follow up to commit c4781dc3d1cf ("Kbuild: enable -fms-extensions") but in a separate change due to being substantially different from the initial submission. There are many places within the kernel that use their own CFLAGS instead of the main KBUILD_CFLAGS, meaning code written with the main kernel's use of '-fms-extensions' in mind that may be tangentially included in these areas will result in "error: declaration does not declare anything" messages from the compiler. Add '-fms-extensions' to all these areas to ensure consistency, along with -Wno-microsoft-anon-tag to silence clang's warning about use of the extension that the kernel cares about using. parisc does not build with clang so it does not need this warning flag. LoongArch does not need it either because -W flags from KBUILD_FLAGS are pulled into cflags-vdso. Reported-by: Christian Brauner Closes: https://lore.kernel.org/20251030-meerjungfrau-getrocknet-7b46eacc215d@brauner/ Reviewed-by: Christian Brauner Acked-by: Ard Biesheuvel Signed-off-by: Nathan Chancellor --- arch/arm64/kernel/vdso32/Makefile | 3 ++- arch/loongarch/vdso/Makefile | 2 +- arch/parisc/boot/compressed/Makefile | 2 +- arch/powerpc/boot/Makefile | 3 ++- arch/s390/Makefile | 3 ++- arch/s390/purgatory/Makefile | 3 ++- arch/x86/Makefile | 4 +++- arch/x86/boot/compressed/Makefile | 7 +++++-- drivers/firmware/efi/libstub/Makefile | 4 ++-- 9 files changed, 20 insertions(+), 11 deletions(-) diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile index ffa3536581f6..9d0efed91414 100644 --- a/arch/arm64/kernel/vdso32/Makefile +++ b/arch/arm64/kernel/vdso32/Makefile @@ -63,7 +63,7 @@ VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ $(filter -Werror,$(KBUILD_CPPFLAGS)) \ -Werror-implicit-function-declaration \ -Wno-format-security \ - -std=gnu11 + -std=gnu11 -fms-extensions VDSO_CFLAGS += -O2 # Some useful compiler-dependent flags from top-level Makefile VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign) @@ -71,6 +71,7 @@ VDSO_CFLAGS += -fno-strict-overflow VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes) VDSO_CFLAGS += -Werror=date-time VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types) +VDSO_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag) # Compile as THUMB2 or ARM. Unwinding via frame-pointers in THUMB2 is # unreliable. diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile index d8316f993482..c0cc3ca5da9f 100644 --- a/arch/loongarch/vdso/Makefile +++ b/arch/loongarch/vdso/Makefile @@ -19,7 +19,7 @@ ccflags-vdso := \ cflags-vdso := $(ccflags-vdso) \ -isystem $(shell $(CC) -print-file-name=include) \ $(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \ - -std=gnu11 -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \ + -std=gnu11 -fms-extensions -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \ -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \ $(call cc-option, -fno-asynchronous-unwind-tables) \ $(call cc-option, -fno-stack-protector) diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile index 17c42d718eb3..f8481e4e9d21 100644 --- a/arch/parisc/boot/compressed/Makefile +++ b/arch/parisc/boot/compressed/Makefile @@ -18,7 +18,7 @@ KBUILD_CFLAGS += -fno-PIE -mno-space-regs -mdisable-fpregs -Os ifndef CONFIG_64BIT KBUILD_CFLAGS += -mfast-indirect-calls endif -KBUILD_CFLAGS += -std=gnu11 +KBUILD_CFLAGS += -std=gnu11 -fms-extensions LDFLAGS_vmlinux := -X -e startup --as-needed -T $(obj)/vmlinux: $(obj)/vmlinux.lds $(addprefix $(obj)/, $(OBJECTS)) $(LIBGCC) FORCE diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile index c47b78c1d3e7..f1a4761ebd44 100644 --- a/arch/powerpc/boot/Makefile +++ b/arch/powerpc/boot/Makefile @@ -70,7 +70,7 @@ BOOTCPPFLAGS := -nostdinc $(LINUXINCLUDE) BOOTCPPFLAGS += -isystem $(shell $(BOOTCC) -print-file-name=include) BOOTCFLAGS := $(BOOTTARGETFLAGS) \ - -std=gnu11 \ + -std=gnu11 -fms-extensions \ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ -fno-strict-aliasing -O2 \ -msoft-float -mno-altivec -mno-vsx \ @@ -86,6 +86,7 @@ BOOTARFLAGS := -crD ifdef CONFIG_CC_IS_CLANG BOOTCFLAGS += $(CLANG_FLAGS) +BOOTCFLAGS += -Wno-microsoft-anon-tag BOOTAFLAGS += $(CLANG_FLAGS) endif diff --git a/arch/s390/Makefile b/arch/s390/Makefile index b4769241332b..8578361133a4 100644 --- a/arch/s390/Makefile +++ b/arch/s390/Makefile @@ -22,7 +22,7 @@ KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__ ifndef CONFIG_AS_IS_LLVM KBUILD_AFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),$(aflags_dwarf)) endif -KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11 +KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11 -fms-extensions KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY KBUILD_CFLAGS_DECOMPRESSOR += -D__DECOMPRESSOR KBUILD_CFLAGS_DECOMPRESSOR += -Wno-pointer-sign @@ -35,6 +35,7 @@ KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-membe KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g) KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,)) KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_NO_ARRAY_BOUNDS),-Wno-array-bounds) +KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag) UTS_MACHINE := s390x STACK_SIZE := $(if $(CONFIG_KASAN),65536,$(if $(CONFIG_KMSAN),65536,16384)) diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile index bd39b36e7bd6..0c196a5b194a 100644 --- a/arch/s390/purgatory/Makefile +++ b/arch/s390/purgatory/Makefile @@ -13,7 +13,7 @@ CFLAGS_sha256.o := -D__NO_FORTIFY $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE $(call if_changed_rule,as_o_S) -KBUILD_CFLAGS := -std=gnu11 -fno-strict-aliasing -Wall -Wstrict-prototypes +KBUILD_CFLAGS := -std=gnu11 -fms-extensions -fno-strict-aliasing -Wall -Wstrict-prototypes KBUILD_CFLAGS += -Wno-pointer-sign -Wno-sign-compare KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding KBUILD_CFLAGS += -Os -m64 -msoft-float -fno-common @@ -21,6 +21,7 @@ KBUILD_CFLAGS += -fno-stack-protector KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING KBUILD_CFLAGS += -D__DISABLE_EXPORTS KBUILD_CFLAGS += $(CLANG_FLAGS) +KBUILD_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag) KBUILD_CFLAGS += $(call cc-option,-fno-PIE) KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS)) KBUILD_AFLAGS += -D__DISABLE_EXPORTS diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 4db7e4bf69f5..e20e25b8b16c 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -48,7 +48,8 @@ endif # How to compile the 16-bit code. Note we always compile for -march=i386; # that way we can complain to the user if the CPU is insufficient. -REALMODE_CFLAGS := -std=gnu11 -m16 -g -Os -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \ +REALMODE_CFLAGS := -std=gnu11 -fms-extensions -m16 -g -Os \ + -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \ -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \ -fno-strict-aliasing -fomit-frame-pointer -fno-pic \ -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none) @@ -60,6 +61,7 @@ REALMODE_CFLAGS += $(cc_stack_align4) REALMODE_CFLAGS += $(CLANG_FLAGS) ifdef CONFIG_CC_IS_CLANG REALMODE_CFLAGS += -Wno-gnu +REALMODE_CFLAGS += -Wno-microsoft-anon-tag endif export REALMODE_CFLAGS diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 74657589264d..68f9d7a1683b 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -25,7 +25,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ # avoid errors with '-march=i386', and future flags may depend on the target to # be valid. KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS) -KBUILD_CFLAGS += -std=gnu11 +KBUILD_CFLAGS += -std=gnu11 -fms-extensions KBUILD_CFLAGS += -fno-strict-aliasing -fPIE KBUILD_CFLAGS += -Wundef KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING @@ -36,7 +36,10 @@ KBUILD_CFLAGS += -mno-mmx -mno-sse KBUILD_CFLAGS += -ffreestanding -fshort-wchar KBUILD_CFLAGS += -fno-stack-protector KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) -KBUILD_CFLAGS += $(call cc-disable-warning, gnu) +ifdef CONFIG_CC_IS_CLANG +KBUILD_CFLAGS += -Wno-gnu +KBUILD_CFLAGS += -Wno-microsoft-anon-tag +endif KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 94b05e4451dd..7d15a85d579f 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile @@ -11,12 +11,12 @@ cflags-y := $(KBUILD_CFLAGS) cflags-$(CONFIG_X86_32) := -march=i386 cflags-$(CONFIG_X86_64) := -mcmodel=small -cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -std=gnu11 \ +cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -std=gnu11 -fms-extensions \ -fPIC -fno-strict-aliasing -mno-red-zone \ -mno-mmx -mno-sse -fshort-wchar \ -Wno-pointer-sign \ $(call cc-disable-warning, address-of-packed-member) \ - $(call cc-disable-warning, gnu) \ + $(if $(CONFIG_CC_IS_CLANG),-Wno-gnu -Wno-microsoft-anon-tag) \ -fno-asynchronous-unwind-tables \ $(CLANG_FLAGS) From b244358e9a1cd61276b8785b1b4275f1f45a1dc2 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Nov 2025 14:51:23 +0100 Subject: [PATCH 4/7] slab: separate struct freelist_tid from kmem_cache_cpu In kmem_cache_cpu we currently have a union of the freelist+tid pair with freelist_aba_t, relying implicitly on the type compatibility with the freelist+counters pair used in freelist_aba_t. To allow further changes to freelist_aba_t, we can instead define a separate struct freelist_tid (instead of a typedef, per the coding style) for kmem_cache_cpu, as that affects only a single helper __update_cpu_freelist_fast(). We can add the resulting struct freelist_tid to kmem_cache_cpu as unnamed field thanks to -fms-extensions, so that freelist and tid fields can still be accessed directly. Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- mm/slub.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 074abe8e79f8..5f6408c9e0fd 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -411,18 +411,22 @@ enum stat_item { }; #ifndef CONFIG_SLUB_TINY +struct freelist_tid { + union { + struct { + void *freelist; /* Pointer to next available object */ + unsigned long tid; /* Globally unique transaction id */ + }; + freelist_full_t freelist_tid; + }; +}; + /* * When changing the layout, make sure freelist and tid are still compatible * with this_cpu_cmpxchg_double() alignment requirements. */ struct kmem_cache_cpu { - union { - struct { - void **freelist; /* Pointer to next available object */ - unsigned long tid; /* Globally unique transaction id */ - }; - freelist_aba_t freelist_tid; - }; + struct freelist_tid; struct slab *slab; /* The slab from which we are allocating */ #ifdef CONFIG_SLUB_CPU_PARTIAL struct slab *partial; /* Partially allocated slabs */ @@ -4367,11 +4371,11 @@ __update_cpu_freelist_fast(struct kmem_cache *s, void *freelist_old, void *freelist_new, unsigned long tid) { - freelist_aba_t old = { .freelist = freelist_old, .counter = tid }; - freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) }; + struct freelist_tid old = { .freelist = freelist_old, .tid = tid }; + struct freelist_tid new = { .freelist = freelist_new, .tid = next_tid(tid) }; - return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid.full, - &old.full, new.full); + return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid, + &old.freelist_tid, new.freelist_tid); } /* From 3993ca9d6495e1e4d6fdaffc1bba0271059940c4 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Nov 2025 14:51:24 +0100 Subject: [PATCH 5/7] slab: turn freelist_aba_t to a struct and fully define counters there In struct slab we currently have freelist and counters pair, where counters itself is a union of unsigned long with a sub-struct of several smaller fields. Then for the usage with double cmpxchg we have freelist_aba_t that duplicates the definition of the freelist+counters with implicitly the same layout as the full definition in struct slab. Thanks to -fms-extension we can now move the full counters definition to freelist_aba_t (while changing it to struct freelist_counters as a typedef is unnecessary and discouraged) and replace the relevant part in struct slab to an unnamed reference to it. The immediate benefit is the removal of duplication and no longer relying on the same layout implicitly. It also allows further cleanups thanks to having the full definition of counters in struct freelist_counters. Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- mm/slab.h | 52 ++++++++++++++++++++++++---------------------------- mm/slub.c | 8 +++++--- 2 files changed, 29 insertions(+), 31 deletions(-) diff --git a/mm/slab.h b/mm/slab.h index 078daecc7cf5..42627b87d50c 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -40,13 +40,29 @@ typedef u64 freelist_full_t; * Freelist pointer and counter to cmpxchg together, avoids the typical ABA * problems with cmpxchg of just a pointer. */ -typedef union { - struct { - void *freelist; - unsigned long counter; +struct freelist_counters { + union { + struct { + void *freelist; + union { + unsigned long counters; + struct { + unsigned inuse:16; + unsigned objects:15; + /* + * If slab debugging is enabled then the + * frozen bit can be reused to indicate + * that the slab was corrupted + */ + unsigned frozen:1; + }; + }; + }; +#ifdef system_has_freelist_aba + freelist_full_t freelist_counters; +#endif }; - freelist_full_t full; -} freelist_aba_t; +}; /* Reuses the bits in struct page */ struct slab { @@ -69,27 +85,7 @@ struct slab { #endif }; /* Double-word boundary */ - union { - struct { - void *freelist; /* first free object */ - union { - unsigned long counters; - struct { - unsigned inuse:16; - unsigned objects:15; - /* - * If slab debugging is enabled then the - * frozen bit can be reused to indicate - * that the slab was corrupted - */ - unsigned frozen:1; - }; - }; - }; -#ifdef system_has_freelist_aba - freelist_aba_t freelist_counter; -#endif - }; + struct freelist_counters; }; struct rcu_head rcu_head; }; @@ -114,7 +110,7 @@ SLAB_MATCH(_unused_slab_obj_exts, obj_exts); #undef SLAB_MATCH static_assert(sizeof(struct slab) <= sizeof(struct page)); #if defined(system_has_freelist_aba) -static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t))); +static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(struct freelist_counters))); #endif /** diff --git a/mm/slub.c b/mm/slub.c index 5f6408c9e0fd..8330e4f8b3b2 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -764,10 +764,12 @@ __update_freelist_fast(struct slab *slab, void *freelist_new, unsigned long counters_new) { #ifdef system_has_freelist_aba - freelist_aba_t old = { .freelist = freelist_old, .counter = counters_old }; - freelist_aba_t new = { .freelist = freelist_new, .counter = counters_new }; + struct freelist_counters old = { .freelist = freelist_old, .counters = counters_old }; + struct freelist_counters new = { .freelist = freelist_new, .counters = counters_new }; - return try_cmpxchg_freelist(&slab->freelist_counter.full, &old.full, new.full); + return try_cmpxchg_freelist(&slab->freelist_counters, + &old.freelist_counters, + new.freelist_counters); #else return false; #endif From 32cf9f21828a752a364b2698ec66f8532cd66c52 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Nov 2025 14:51:25 +0100 Subject: [PATCH 6/7] slab: use struct freelist_counters for local variables instead of struct slab In several functions we declare local struct slab variables so we can work with the freelist and counters fields (including the sub-counters that are in the union) comfortably. With struct freelist_counters containing the full counters definition, we can now reduce the local variables to that type as we don't need the other fields in struct slab. Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- mm/slub.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 8330e4f8b3b2..a55e0af26ec7 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3725,8 +3725,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab, void *nextfree, *freelist_iter, *freelist_tail; int tail = DEACTIVATE_TO_HEAD; unsigned long flags = 0; - struct slab new; - struct slab old; + struct freelist_counters old, new; if (READ_ONCE(slab->freelist)) { stat(s, DEACTIVATE_REMOTE_FREES); @@ -4390,7 +4389,7 @@ __update_cpu_freelist_fast(struct kmem_cache *s, */ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab) { - struct slab new; + struct freelist_counters new; unsigned long counters; void *freelist; @@ -4418,7 +4417,7 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab) */ static inline void *freeze_slab(struct kmem_cache *s, struct slab *slab) { - struct slab new; + struct freelist_counters new; unsigned long counters; void *freelist; @@ -5867,7 +5866,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, { void *old_head; bool was_frozen, was_full; - struct slab new; + struct freelist_counters new; unsigned long counters; struct kmem_cache_node *n = NULL; unsigned long flags; From c33196c9429a1db5bc6cded27b6286f341ad6be0 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Nov 2025 14:51:26 +0100 Subject: [PATCH 7/7] slab: use struct freelist_counters as parameters in relevant functions In functions such as [__]slab_update_freelist() and __slab_update_freelist_fast/slow() we pass old and new freelist and counters as 4 separate parameters. The underlying __update_freelist_fast() then constructs struct freelist_counters variables for passing the full freelist+counter combinations to cmpxchg double. In most cases we actually start with struct freelist_counters variables, but then pass the individual fields, only to construct new struct freelist_counters variables. While it's all inlined and thus should be efficient, we can simplify this code. Thus replace the 4 parameters for individual fields with two pointers to struct freelist_counters wherever applicable. __update_freelist_fast() can then pass them directly to try_cmpxchg_freelist(). The code is also more obvious as the pattern becomes unified such that we set up "old" and "new" struct freelist_counters variables upfront as we fully need them to be, and simply call [__]slab_update_freelist() on them. Previously some of the "new" values would be hidden among the many parameters and thus make it harder to figure out what the code does. Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- mm/slub.c | 126 ++++++++++++++++++++++-------------------------------- 1 file changed, 52 insertions(+), 74 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index a55e0af26ec7..ddd71f4937fa 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -759,34 +759,29 @@ static __always_inline void slab_unlock(struct slab *slab) } static inline bool -__update_freelist_fast(struct slab *slab, - void *freelist_old, unsigned long counters_old, - void *freelist_new, unsigned long counters_new) +__update_freelist_fast(struct slab *slab, struct freelist_counters *old, + struct freelist_counters *new) { #ifdef system_has_freelist_aba - struct freelist_counters old = { .freelist = freelist_old, .counters = counters_old }; - struct freelist_counters new = { .freelist = freelist_new, .counters = counters_new }; - return try_cmpxchg_freelist(&slab->freelist_counters, - &old.freelist_counters, - new.freelist_counters); + &old->freelist_counters, + new->freelist_counters); #else return false; #endif } static inline bool -__update_freelist_slow(struct slab *slab, - void *freelist_old, unsigned long counters_old, - void *freelist_new, unsigned long counters_new) +__update_freelist_slow(struct slab *slab, struct freelist_counters *old, + struct freelist_counters *new) { bool ret = false; slab_lock(slab); - if (slab->freelist == freelist_old && - slab->counters == counters_old) { - slab->freelist = freelist_new; - slab->counters = counters_new; + if (slab->freelist == old->freelist && + slab->counters == old->counters) { + slab->freelist = new->freelist; + slab->counters = new->counters; ret = true; } slab_unlock(slab); @@ -802,22 +797,18 @@ __update_freelist_slow(struct slab *slab, * interrupt the operation. */ static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *slab, - void *freelist_old, unsigned long counters_old, - void *freelist_new, unsigned long counters_new, - const char *n) + struct freelist_counters *old, struct freelist_counters *new, const char *n) { bool ret; if (USE_LOCKLESS_FAST_PATH()) lockdep_assert_irqs_disabled(); - if (s->flags & __CMPXCHG_DOUBLE) { - ret = __update_freelist_fast(slab, freelist_old, counters_old, - freelist_new, counters_new); - } else { - ret = __update_freelist_slow(slab, freelist_old, counters_old, - freelist_new, counters_new); - } + if (s->flags & __CMPXCHG_DOUBLE) + ret = __update_freelist_fast(slab, old, new); + else + ret = __update_freelist_slow(slab, old, new); + if (likely(ret)) return true; @@ -832,21 +823,17 @@ static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *sla } static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab, - void *freelist_old, unsigned long counters_old, - void *freelist_new, unsigned long counters_new, - const char *n) + struct freelist_counters *old, struct freelist_counters *new, const char *n) { bool ret; if (s->flags & __CMPXCHG_DOUBLE) { - ret = __update_freelist_fast(slab, freelist_old, counters_old, - freelist_new, counters_new); + ret = __update_freelist_fast(slab, old, new); } else { unsigned long flags; local_irq_save(flags); - ret = __update_freelist_slow(slab, freelist_old, counters_old, - freelist_new, counters_new); + ret = __update_freelist_slow(slab, old, new); local_irq_restore(flags); } if (likely(ret)) @@ -3774,10 +3761,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab, } else { new.freelist = old.freelist; } - } while (!slab_update_freelist(s, slab, - old.freelist, old.counters, - new.freelist, new.counters, - "unfreezing slab")); + } while (!slab_update_freelist(s, slab, &old, &new, "unfreezing slab")); /* * Stage three: Manipulate the slab list based on the updated state. @@ -4389,27 +4373,24 @@ __update_cpu_freelist_fast(struct kmem_cache *s, */ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab) { - struct freelist_counters new; - unsigned long counters; - void *freelist; + struct freelist_counters old, new; lockdep_assert_held(this_cpu_ptr(&s->cpu_slab->lock)); do { - freelist = slab->freelist; - counters = slab->counters; + old.freelist = slab->freelist; + old.counters = slab->counters; - new.counters = counters; + new.freelist = NULL; + new.counters = old.counters; - new.inuse = slab->objects; - new.frozen = freelist != NULL; + new.inuse = old.objects; + new.frozen = old.freelist != NULL; - } while (!__slab_update_freelist(s, slab, - freelist, counters, - NULL, new.counters, - "get_freelist")); - return freelist; + } while (!__slab_update_freelist(s, slab, &old, &new, "get_freelist")); + + return old.freelist; } /* @@ -4417,26 +4398,22 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab) */ static inline void *freeze_slab(struct kmem_cache *s, struct slab *slab) { - struct freelist_counters new; - unsigned long counters; - void *freelist; + struct freelist_counters old, new; do { - freelist = slab->freelist; - counters = slab->counters; + old.freelist = slab->freelist; + old.counters = slab->counters; - new.counters = counters; + new.freelist = NULL; + new.counters = old.counters; VM_BUG_ON(new.frozen); - new.inuse = slab->objects; + new.inuse = old.objects; new.frozen = 1; - } while (!slab_update_freelist(s, slab, - freelist, counters, - NULL, new.counters, - "freeze_slab")); + } while (!slab_update_freelist(s, slab, &old, &new, "freeze_slab")); - return freelist; + return old.freelist; } /* @@ -5864,10 +5841,8 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, unsigned long addr) { - void *old_head; bool was_frozen, was_full; - struct freelist_counters new; - unsigned long counters; + struct freelist_counters old, new; struct kmem_cache_node *n = NULL; unsigned long flags; bool on_node_partial; @@ -5891,13 +5866,19 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, spin_unlock_irqrestore(&n->list_lock, flags); n = NULL; } - old_head = slab->freelist; - counters = slab->counters; - set_freepointer(s, tail, old_head); - new.counters = counters; - was_frozen = !!new.frozen; - was_full = (old_head == NULL); + + old.freelist = slab->freelist; + old.counters = slab->counters; + + was_full = (old.freelist == NULL); + was_frozen = old.frozen; + + set_freepointer(s, tail, old.freelist); + + new.freelist = head; + new.counters = old.counters; new.inuse -= cnt; + /* * Might need to be taken off (due to becoming empty) or added * to (due to not being full anymore) the partial list. @@ -5926,10 +5907,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, } } - } while (!slab_update_freelist(s, slab, - old_head, counters, - head, new.counters, - "__slab_free")); + } while (!slab_update_freelist(s, slab, &old, &new, "__slab_free")); if (likely(!n)) {