+ reboot-halt-when-power-off-fails.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: reboot: halt when power off fails
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     reboot-halt-when-power-off-fails.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/reboot-halt-when-power-off-fails.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Breno Leitao <leitao@debian.org>
Subject: reboot: halt when power off fails
Date: Tue, 10 Nov 2026 07:24:34 -0800

The reboot syscall calls do_exit(0) when kernel_power_off() returns.  That
happens when no power off handler takes the machine down, since
machine_power_off() returns to its caller on x86, arm, arm64 and sh.

For example, an x86 kernel built with CONFIG_ACPI_REDUCED_HARDWARE_ONLY
cannot power off QEMU's pc and q35 machines.  Their FADT is not
hardware-reduced, so acpi_power_off() is still registered.  But the legacy
sleep code is compiled out and the FADT has no sleep control register, so
acpi_enter_sleep_state() returns AE_NOT_EXIST.

On x86, arm and arm64, interrupts are disabled by then, and do_exit()
warns. syzbot hit this on a GCE VM:

  ACPI: PM: Preparing to enter system sleep state S5
  kvm: exiting hardware virtualization
  reboot: Power down
  ------------[ cut here ]------------
  irqs_disabled()
  WARNING: kernel/exit.c:930 at do_exit+0x1cf7/0x2ae0 kernel/exit.c:930, CPU#0: init/6193
  CPU: 0 UID: 0 PID: 6193 Comm: init Tainted: G             L      syzkaller #0 PREEMPT(full)
  Call Trace:
   <TASK>
   __do_sys_reboot+0x36e/0x400 kernel/reboot.c:784
   do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

If the caller is init, do_exit() then panics. Exiting does not help
the other callers either: the devices are already shut down, and the
task still holds system_transition_mutex.

Halt instead, as the syscall already does when no power off handler is
registered, and as most other architectures do in machine_power_off().

Use machine_halt() rather than kernel_halt(). kernel_power_off() has
already run the shutdown sequence, and kernel_halt() would call the
reboot notifiers again with interrupts disabled.

Keep the fallback in the syscall.  hw_failure_emergency_action_func()
relies on kernel_power_off() returning, so that it can try an emergency
restart.

Link: https://lore.kernel.org/20261110-reboot-make-task-dead-v1-1-af88a3f37bf7@debian.org
Link: https://lore.kernel.org/all/20260713062332.21131-1-include@grrlz.net/
Fixes: 001c28e57187 ("exit: Detect and fix irq disabled state in oops")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: <syzbot+8fdf0d8e10bdde1c2e88@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=8fdf0d8e10bdde1c2e88
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/all/20250404152006.GF3720@redhat.com/
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Bradley Morgan <bradley.morgan@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Konrad Dybcio <angelogioacchino.delregno@collabora.com>
Cc: <stable@vger.kernel.org>
---

 kernel/reboot.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/reboot.c~reboot-halt-when-power-off-fails
+++ a/kernel/reboot.c
@@ -791,6 +791,9 @@ SYSCALL_DEFINE4(reboot, int, magic1, int
 
 	case LINUX_REBOOT_CMD_POWER_OFF:
 		kernel_power_off();
+		pr_emerg("Power off failed: System halted instead\n");
+		/* kernel_power_off() already ran the shutdown, only halt. */
+		machine_halt();
 		do_exit(0);
 		break;
 
_

Patches currently in -mm which might be from leitao@debian.org are

mm-kmemleak-scan-modified-objects-as-soon-as-they-are-grayed.patch
tools-mm-add-hwpoison-panic-tool.patch
mm-split-out-memory-failure-declarations-from-internalh.patch
mm-kmemleak-drop-kmemleak_lock-in-scan_block-when-it-is-contended.patch
ratelimit-fix-data-race-on-burst-in-___ratelimit.patch
stackdepot-dont-warn-when-the-depot-runs-out-of-pools.patch
reboot-halt-when-power-off-fails.patch