From: Lance Yang lance.yang@linux.dev

The blocker tracking mechanism assumes that lock pointers are at least 4-byte aligned to use their lower bits for type encoding.

However, as reported by Geert Uytterhoeven, some architectures like m68k only guarantee 2-byte alignment of 32-bit values. This breaks the assumption and causes two related WARN_ON_ONCE checks to trigger.

To fix this, enforce a minimum of 4-byte alignment on the core lock structures supported by the blocker tracking mechanism. This ensures the algorithm's alignment assumption now holds true on all architectures.

This patch adds __aligned(4) to the definitions of "struct mutex", "struct semaphore", and "struct rw_semaphore", resolving the warnings.

Thanks to Geert for bisecting!

Reported-by: Geert Uytterhoeven geert@linux-m68k.org Closes: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc... Fixes: e711faaafbe5 ("hung_task: replace blocker_mutex with encoded blocker") Cc: stable@vger.kernel.org Signed-off-by: Lance Yang lance.yang@linux.dev --- include/linux/mutex_types.h | 2 +- include/linux/rwsem.h | 2 +- include/linux/semaphore.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/mutex_types.h b/include/linux/mutex_types.h index fdf7f515fde8..de798bfbc4c7 100644 --- a/include/linux/mutex_types.h +++ b/include/linux/mutex_types.h @@ -51,7 +51,7 @@ struct mutex { #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif -}; +} __aligned(4); /* For hung_task blocker tracking, which encodes type in LSBs */

#else /* !CONFIG_PREEMPT_RT */ /* diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index f1aaf676a874..f6ecf4a4710d 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -64,7 +64,7 @@ struct rw_semaphore { #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif -}; +} __aligned(4); /* For hung_task blocker tracking, which encodes type in LSBs */

#define RWSEM_UNLOCKED_VALUE 0UL #define RWSEM_WRITER_LOCKED (1UL << 0) diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index 89706157e622..ac9b9c87bfb7 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -20,7 +20,7 @@ struct semaphore { #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER unsigned long last_holder; #endif -}; +} __aligned(4); /* For hung_task blocker tracking, which encodes type in LSBs */

#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER #define __LAST_HOLDER_SEMAPHORE_INITIALIZER \