6.17-stable review patch. If anyone has any objections, please let me know.
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From: Lance Yang lance.yang@linux.dev
commit c97513cddcfc235f2522617980838e500af21d01 upstream.
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 Eero Tamminen, 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, the runtime checks are adjusted to silently ignore any lock that is not 4-byte aligned, effectively disabling the feature in such cases and avoiding the related warnings.
Thanks to Geert Uytterhoeven for bisecting!
Link: https://lkml.kernel.org/r/20250909145243.17119-1-lance.yang@linux.dev Fixes: e711faaafbe5 ("hung_task: replace blocker_mutex with encoded blocker") Signed-off-by: Lance Yang lance.yang@linux.dev Reported-by: Eero Tamminen oak@helsinkinet.fi Closes: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc... Reviewed-by: Masami Hiramatsu (Google) mhiramat@kernel.org Cc: John Paul Adrian Glaubitz glaubitz@physik.fu-berlin.de Cc: Anna Schumaker anna.schumaker@oracle.com Cc: Boqun Feng boqun.feng@gmail.com Cc: Finn Thain fthain@linux-m68k.org Cc: Geert Uytterhoeven geert@linux-m68k.org Cc: Ingo Molnar mingo@redhat.com Cc: Joel Granados joel.granados@kernel.org Cc: John Stultz jstultz@google.com Cc: Kent Overstreet kent.overstreet@linux.dev Cc: Lance Yang lance.yang@linux.dev Cc: Mingzhe Yang mingzhe.yang@ly.com Cc: Peter Zijlstra peterz@infradead.org Cc: Sergey Senozhatsky senozhatsky@chromium.org Cc: Steven Rostedt rostedt@goodmis.org Cc: Tomasz Figa tfiga@chromium.org Cc: Waiman Long longman@redhat.com Cc: Will Deacon will@kernel.org Cc: Yongliang Gao leonylgao@tencent.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/hung_task.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/include/linux/hung_task.h b/include/linux/hung_task.h index 34e615c76ca5..c4403eeb7144 100644 --- a/include/linux/hung_task.h +++ b/include/linux/hung_task.h @@ -20,6 +20,10 @@ * always zero. So we can use these bits to encode the specific blocking * type. * + * Note that on architectures where this is not guaranteed, or for any + * unaligned lock, this tracking mechanism is silently skipped for that + * lock. + * * Type encoding: * 00 - Blocked on mutex (BLOCKER_TYPE_MUTEX) * 01 - Blocked on semaphore (BLOCKER_TYPE_SEM) @@ -45,7 +49,7 @@ static inline void hung_task_set_blocker(void *lock, unsigned long type) * If the lock pointer matches the BLOCKER_TYPE_MASK, return * without writing anything. */ - if (WARN_ON_ONCE(lock_ptr & BLOCKER_TYPE_MASK)) + if (lock_ptr & BLOCKER_TYPE_MASK) return;
WRITE_ONCE(current->blocker, lock_ptr | type); @@ -53,8 +57,6 @@ static inline void hung_task_set_blocker(void *lock, unsigned long type)
static inline void hung_task_clear_blocker(void) { - WARN_ON_ONCE(!READ_ONCE(current->blocker)); - WRITE_ONCE(current->blocker, 0UL); }