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[77.2.57.64]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-495653c98ebsm175819785e9.13.2026.07.22.21.12.14 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 22 Jul 2026 21:12:15 -0700 (PDT) From: Karl Mehltretter To: Geert Uytterhoeven Cc: Karl Mehltretter , linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org Subject: [PATCH] m68k: Fix backtraces for non-running tasks Date: Thu, 23 Jul 2026 06:10:55 +0200 Message-Id: <20260723041055.47289-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When no stack pointer is supplied, show_stack() starts at thread.esp0. This is the saved userspace register frame, not where a task was switched out. For kernel threads it points to the zeroed frame created by copy_thread(), so sched_show_task() prints no useful backtrace. Use thread.ksp for non-current tasks. It is saved by switch_to() and is already used by __get_wchan(). For current, start at the current stack frame, as is already done when no task is supplied. Tested on qemu-system-m68k -M virt using SysRq-t. All task dumps contained resolved frames. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Karl Mehltretter --- diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c index d2f25e8895e5..60759ba3cbd4 100644 --- a/arch/m68k/kernel/traps.c +++ b/arch/m68k/kernel/traps.c @@ -936,8 +936,8 @@ void show_stack(struct task_struct *task, unsigned long= *stack, int i; =20 if (!stack) { - if (task) - stack =3D (unsigned long *)task->thread.esp0; + if (task && task !=3D current) + stack =3D (unsigned long *)task->thread.ksp; else stack =3D (unsigned long *)&stack; }