* + atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch added to mm-nonmm-unstable branch
@ 2025-12-27 15:09 Andrew Morton
0 siblings, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2025-12-27 15:09 UTC (permalink / raw)
To: mm-commits, ysato, yonghong.song, will, tglx, stefan.kristiansson,
song, shorne, sdf, sashal, peterz, mingo, martin.lau,
mark.rutland, kpsingh, jonas, jolsa, john.fastabend, hpa, haoluo,
guoren, glaubitz, geert, gary, eddyz87, dinguyen, dave.hansen,
daniel, dalias, bp, boqun.feng, ast, arnd, ardb, andrii, fthain,
akpm
The patch titled
Subject: atomic: specify alignment for atomic_t and atomic64_t
has been added to the -mm mm-nonmm-unstable branch. Its filename is
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Finn Thain <fthain@linux-m68k.org>
Subject: atomic: specify alignment for atomic_t and atomic64_t
Date: Wed, 31 Dec 2025 19:25:42 +1100
Some recent commits incorrectly assumed 4-byte alignment of locks. That
assumption fails on Linux/m68k (and, interestingly, would have failed on
Linux/cris also). The jump label implementation makes a similar alignment
assumption.
The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures. But
atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned on
m68k.
This patch brings a little uniformity by specifying natural alignment for
atomic types. One benefit is that atomic64_t variables do not get split
across a page boundary. The cost is that some structs grow which leads to
cache misses and wasted memory.
Link: https://lkml.kernel.org/r/88df424bfb93bdabe73bf91f5985c5b89f04d123.1767169542.git.fthain@linux-m68k.org
Link: https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7w@mail.gmail.com
Link: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: Hao Luo <haoluo@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin (Microsoft) <sashal@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/asm-generic/atomic64.h | 2 +-
include/linux/types.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/include/asm-generic/atomic64.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/asm-generic/atomic64.h
@@ -10,7 +10,7 @@
#include <linux/types.h>
typedef struct {
- s64 counter;
+ s64 __aligned(sizeof(s64)) counter;
} atomic64_t;
#define ATOMIC64_INIT(i) { (i) }
--- a/include/linux/types.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/linux/types.h
@@ -179,7 +179,7 @@ typedef phys_addr_t resource_size_t;
typedef unsigned long irq_hw_number_t;
typedef struct {
- int counter;
+ int __aligned(sizeof(int)) counter;
} atomic_t;
#define ATOMIC_INIT(i) { (i) }
_
Patches currently in -mm which might be from fthain@linux-m68k.org are
bpf-explicitly-align-bpf_res_spin_lock.patch
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
atomic-add-option-for-weaker-alignment-check.patch
^ permalink raw reply [flat|nested] 3+ messages in thread* + atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch added to mm-nonmm-unstable branch
@ 2026-01-13 23:34 Andrew Morton
0 siblings, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2026-01-13 23:34 UTC (permalink / raw)
To: mm-commits, ysato, yonghong.song, will, tglx, stefan.kristiansson,
song, shorne, sdf, sashal, peterz, mingo, martin.lau,
mark.rutland, kpsingh, jonas, jolsa, john.fastabend, hpa, haoluo,
guoren, glaubitz, geert, gary, eddyz87, dinguyen, dave.hansen,
daniel, dalias, bp, boqun.feng, ast, arnd, ardb, andrii, fthain,
akpm
The patch titled
Subject: atomic: specify alignment for atomic_t and atomic64_t
has been added to the -mm mm-nonmm-unstable branch. Its filename is
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Finn Thain <fthain@linux-m68k.org>
Subject: atomic: specify alignment for atomic_t and atomic64_t
Date: Tue, 13 Jan 2026 16:22:28 +1100
Some recent commits incorrectly assumed 4-byte alignment of locks. That
assumption fails on Linux/m68k (and, interestingly, would have failed on
Linux/cris also). The jump label implementation makes a similar alignment
assumption.
The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures. But
atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned on
m68k.
This patch brings a little uniformity by specifying natural alignment for
atomic types. One benefit is that atomic64_t variables do not get split
across a page boundary. The cost is that some structs grow which leads to
cache misses and wasted memory.
See also, commit bbf2a330d92c ("x86: atomic64: The atomic64_t data type
should be 8 bytes aligned on 32-bit too").
Link: https://lkml.kernel.org/r/a76bc24a4e7c1d8112d7d5fa8d14e4b694a0e90c.1768281748.git.fthain@linux-m68k.org
Link: https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7w@mail.gmail.com
Link: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Guo Ren <guoren@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: Hao Luo <haoluo@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin (Microsoft) <sashal@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/asm-generic/atomic64.h | 2 +-
include/linux/types.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/include/asm-generic/atomic64.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/asm-generic/atomic64.h
@@ -10,7 +10,7 @@
#include <linux/types.h>
typedef struct {
- s64 counter;
+ s64 __aligned(sizeof(s64)) counter;
} atomic64_t;
#define ATOMIC64_INIT(i) { (i) }
--- a/include/linux/types.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/linux/types.h
@@ -179,7 +179,7 @@ typedef phys_addr_t resource_size_t;
typedef unsigned long irq_hw_number_t;
typedef struct {
- int counter;
+ int __aligned(sizeof(int)) counter;
} atomic_t;
#define ATOMIC_INIT(i) { (i) }
_
Patches currently in -mm which might be from fthain@linux-m68k.org are
bpf-explicitly-align-bpf_res_spin_lock.patch
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
atomic-add-option-for-weaker-alignment-check.patch
^ permalink raw reply [flat|nested] 3+ messages in thread* + atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch added to mm-nonmm-unstable branch
@ 2025-12-16 19:49 Andrew Morton
0 siblings, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2025-12-16 19:49 UTC (permalink / raw)
To: mm-commits, ysato, yonghong.song, will, stefan.kristiansson, song,
shorne, sdf, peterz, martin.lau, mark.rutland, kpsingh, jonas,
jolsa, john.fastabend, haoluo, guoren, glaubitz, geert, gary,
eddyz87, dinguyen, daniel, dalias, boqun.feng, ast, arnd, andrii,
fthain, akpm
The patch titled
Subject: atomic: specify alignment for atomic_t and atomic64_t
has been added to the -mm mm-nonmm-unstable branch. Its filename is
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Finn Thain <fthain@linux-m68k.org>
Subject: atomic: specify alignment for atomic_t and atomic64_t
Date: Tue, 16 Dec 2025 17:31:05 +1100
Some recent commits incorrectly assumed 4-byte alignment of locks. That
assumption fails on Linux/m68k (and, interestingly, would have failed on
Linux/cris also). The jump label implementation makes a similar alignment
assumption.
The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures. But
atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned on
m68k.
This patch brings a little uniformity by specifying natural alignment for
atomic types. One benefit is that atomic64_t variables do not get split
across a page boundary. The cost is that some structs grow which leads to
cache misses and wasted memory.
Link: https://lkml.kernel.org/r/d6cd17b387fa4b4cf9f419ec586ac4756bc7aaeb.1765866665.git.fthain@linux-m68k.org
Link: https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7w@mail.gmail.com
Link: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Will Deacon <will@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/asm-generic/atomic64.h | 2 +-
include/linux/types.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/include/asm-generic/atomic64.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/asm-generic/atomic64.h
@@ -10,7 +10,7 @@
#include <linux/types.h>
typedef struct {
- s64 counter;
+ s64 __aligned(sizeof(s64)) counter;
} atomic64_t;
#define ATOMIC64_INIT(i) { (i) }
--- a/include/linux/types.h~atomic-specify-alignment-for-atomic_t-and-atomic64_t
+++ a/include/linux/types.h
@@ -180,7 +180,7 @@ typedef phys_addr_t resource_size_t;
typedef unsigned long irq_hw_number_t;
typedef struct {
- int counter;
+ int __aligned(sizeof(int)) counter;
} atomic_t;
#define ATOMIC_INIT(i) { (i) }
_
Patches currently in -mm which might be from fthain@linux-m68k.org are
bpf-explicitly-align-bpf_res_spin_lock.patch
atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch
atomic-add-option-for-weaker-alignment-check.patch
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-01-13 23:34 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2025-12-27 15:09 + atomic-specify-alignment-for-atomic_t-and-atomic64_t.patch added to mm-nonmm-unstable branch Andrew Morton
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2026-01-13 23:34 Andrew Morton
2025-12-16 19:49 Andrew Morton
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