From: Peter Zijlstra <peterz@infradead.org>
Add a Kconfig option for debug builds which logs a warning when an
instrumented atomic operation takes place that's misaligned.
Some platforms don't trap for this.
[ fthain: added __DISABLE_EXPORTS conditional and refactored as helper
function. ]
Cc: Sasha Levin <sashal@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/lkml/20250901093600.GF4067720@noisy.programming.kicks-ass.net/
Link: https://lore.kernel.org/linux-next/df9fbd22-a648-ada4-fee0-68fe4325ff82@linux-m68k.org/
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
Checkpatch.pl says...
ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@infradead.org>'
---
Changed since v6:
- Implemented helper function earlier in patch series, as requested by Ard.
- Dropped __DISABLE_BUG_TABLE macro in favour of __DISABLE_EXPORTS, as
requested by Peter.
Changed since v5:
- Add new __DISABLE_BUG_TABLE macro to prevent a build failure on those
architectures which use atomics in pre-boot code like the EFI stub loader:
x86_64-linux-gnu-ld: error: unplaced orphan section `__bug_table' from `arch/x86/boot/compressed/sev-handle-vc.o'
Changed since v2:
- Always check for natural alignment.
---
include/linux/instrumented.h | 11 +++++++++++
lib/Kconfig.debug | 10 ++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
index 711a1f0d1a73..e34b6a557e0a 100644
--- a/include/linux/instrumented.h
+++ b/include/linux/instrumented.h
@@ -7,6 +7,7 @@
#ifndef _LINUX_INSTRUMENTED_H
#define _LINUX_INSTRUMENTED_H
+#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/kasan-checks.h>
#include <linux/kcsan-checks.h>
@@ -55,6 +56,13 @@ static __always_inline void instrument_read_write(const volatile void *v, size_t
kcsan_check_read_write(v, size);
}
+static __always_inline void instrument_atomic_check_alignment(const volatile void *v, size_t size)
+{
+#ifndef __DISABLE_EXPORTS
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ATOMIC) && ((unsigned long)v & (size - 1)));
+#endif
+}
+
/**
* instrument_atomic_read - instrument atomic read access
* @v: address of access
@@ -67,6 +75,7 @@ static __always_inline void instrument_atomic_read(const volatile void *v, size_
{
kasan_check_read(v, size);
kcsan_check_atomic_read(v, size);
+ instrument_atomic_check_alignment(v, size);
}
/**
@@ -81,6 +90,7 @@ static __always_inline void instrument_atomic_write(const volatile void *v, size
{
kasan_check_write(v, size);
kcsan_check_atomic_write(v, size);
+ instrument_atomic_check_alignment(v, size);
}
/**
@@ -95,6 +105,7 @@ static __always_inline void instrument_atomic_read_write(const volatile void *v,
{
kasan_check_write(v, size);
kcsan_check_atomic_read_write(v, size);
+ instrument_atomic_check_alignment(v, size);
}
/**
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ba36939fda79..4b4d1445ef9c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1359,6 +1359,16 @@ config DEBUG_PREEMPT
depending on workload as it triggers debugging routines for each
this_cpu operation. It should only be used for debugging purposes.
+config DEBUG_ATOMIC
+ bool "Debug atomic variables"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here then the kernel will add a runtime alignment check
+ to atomic accesses. Useful for architectures that do not have trap on
+ mis-aligned access.
+
+ This option has potentially significant overhead.
+
menu "Lock Debugging (spinlocks, mutexes, etc...)"
config LOCK_DEBUGGING_SUPPORT
--
2.49.1On Tue, Jan 13, 2026 at 04:22:28PM +1100, Finn Thain wrote: > From: Peter Zijlstra <peterz@infradead.org> > > Add a Kconfig option for debug builds which logs a warning when an > instrumented atomic operation takes place that's misaligned. > Some platforms don't trap for this. > > [ fthain: added __DISABLE_EXPORTS conditional and refactored as helper > function. ] > > Cc: Sasha Levin <sashal@kernel.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Link: https://lore.kernel.org/lkml/20250901093600.GF4067720@noisy.programming.kicks-ass.net/ > Link: https://lore.kernel.org/linux-next/df9fbd22-a648-ada4-fee0-68fe4325ff82@linux-m68k.org/ > Signed-off-by: Finn Thain <fthain@linux-m68k.org> > > --- > Checkpatch.pl says... > ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@infradead.org>' Feel free to add: Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Hi Finn,
On Tue, 13 Jan 2026 at 06:39, Finn Thain <fthain@linux-m68k.org> wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> Add a Kconfig option for debug builds which logs a warning when an
> instrumented atomic operation takes place that's misaligned.
> Some platforms don't trap for this.
>
> [ fthain: added __DISABLE_EXPORTS conditional and refactored as helper
> function. ]
>
> Cc: Sasha Levin <sashal@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Link: https://lore.kernel.org/lkml/20250901093600.GF4067720@noisy.programming.kicks-ass.net/
> Link: https://lore.kernel.org/linux-next/df9fbd22-a648-ada4-fee0-68fe4325ff82@linux-m68k.org/
> Signed-off-by: Finn Thain <fthain@linux-m68k.org>
>
> ---
> Checkpatch.pl says...
> ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@infradead.org>'
Alternatively, you can credit Peter using
Suggested-by: Peter Zijlstra <peterz@infradead.org>
just before the Link-header pointing to his suggestion.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
On Tue, 13 Jan 2026, Geert Uytterhoeven wrote:
> >
> > ---
> > Checkpatch.pl says...
> > ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@infradead.org>'
>
> Alternatively, you can credit Peter using
>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
>
> just before the Link-header pointing to his suggestion.
>
I'll leave that up to Peter as he's both author and maintainer.
If there was to be another revision, perhaps I can add --
Suggested-by-suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
;-)
On Wed, 14 Jan 2026 14:53:33 +1100 (AEDT) Finn Thain <fthain@linux-m68k.org> wrote: > > On Tue, 13 Jan 2026, Geert Uytterhoeven wrote: > > > > > > > --- > > > Checkpatch.pl says... > > > ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@infradead.org>' > > > > Alternatively, you can credit Peter using > > > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > > > just before the Link-header pointing to his suggestion. > > > > I'll leave that up to Peter as he's both author and maintainer. We have his signoff. > If there was to be another revision, perhaps I can add -- > > Suggested-by-suggested-by: Geert Uytterhoeven <geert@linux-m68k.org> edited and added, thanks.
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