linux-kernel - [PATCH] atomic: Specify natural alignment for atomic

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Message-ID: <7d9554bfe2412ed9427bf71ce38a376e06eb9ec4.1756087385.git.fthain@linux-m68k.org>
Date: Mon, 25 Aug 2025 12:03:05 +1000
From: Finn Thain <fthain@...ux-m68k.org>
To: "Andrew Morton" <akpm@...ux-foundation.org>,
    "Lance Yang" <lance.yang@...ux.dev>
Cc: "Geert Uytterhoeven" <geert@...ux-m68k.org>,
    "Masami Hiramatsu" <mhiramat@...nel.org>,
    "Eero Tamminen" <oak@...sinkinet.fi>,
    "Peter Zijlstra" <peterz@...radead.org>,
    "Will Deacon" <will@...nel.org>,
    stable@...r.kernel.org,
    linux-kernel@...r.kernel.org
Subject: [PATCH] atomic: Specify natural alignment for atomic_t

Some recent commits incorrectly assumed the natural alignment of locks.
That assumption fails on Linux/m68k (and, interestingly, would have failed
on Linux/cris also). This leads to spurious warnings from the hang check
code. Fix this bug by adding the necessary 'aligned' attribute.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Lance Yang <lance.yang@...ux.dev>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Eero Tamminen <oak@...sinkinet.fi>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>
Cc: stable@...r.kernel.org
Reported-by: Eero Tamminen <oak@...sinkinet.fi>
Closes: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Fixes: e711faaafbe5 ("hung_task: replace blocker_mutex with encoded blocker")
Signed-off-by: Finn Thain <fthain@...ux-m68k.org>
---
I tested this on m68k using GCC and it fixed the problem for me. AFAIK,
the other architectures naturally align ints already so I'm expecting to
see no effect there.
---
 include/linux/types.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/types.h b/include/linux/types.h
index 6dfdb8e8e4c3..cd5b2b0f4b02 100644
--- a/include/linux/types.h
+++ b/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 counter __aligned(sizeof(int));
 } atomic_t;
 
 #define ATOMIC_INIT(i) { (i) }
-- 
2.49.1