• Eric W. Biederman's avatar
    [PATCH] i386/x86-64: Don't IPI to offline cpus on shutdown · 6e3fbee5
    Eric W. Biederman authored
    So why are we calling smp_send_stop from machine_halt?
    
    We don't.
    
    Looking more closely at the bug report the problem here
    is that halt -p is called which triggers not a halt but
    an attempt to power off.
    
    machine_power_off calls machine_shutdown which calls smp_send_stop.
    
    If pm_power_off is set we should never make it out machine_power_off
    to the call of do_exit.  So pm_power_off must not be set in this case.
    When pm_power_off is not set we expect machine_power_off to devolve
    into machine_halt.
    
    So how do we fix this?
    
    Playing too much with smp_send_stop is dangerous because it
    must also be safe to be called from panic.
    
    It looks like the obviously correct fix is to only call
    machine_shutdown when pm_power_off is defined.  Doing
    that will make Andi's assumption about not scheduling
    true and generally simplify what must be supported.
    
    This turns machine_power_off into a noop like machine_halt
    when pm_power_off is not defined.
    
    If the expected behavior is that sys_reboot(LINUX_REBOOT_CMD_POWER_OFF)
    becomes sys_reboot(LINUX_REBOOT_CMD_HALT) if pm_power_off is NULL
    this is not quite a comprehensive fix as we pass a different parameter
    to the reboot notifier and we set system_state to a different value
    before calling device_shutdown().
    
    Unfortunately any fix more comprehensive I can think of is not
    obviously correct.  The core problem is that there is no architecture
    independent way to detect if machine_power will become a noop, without
    calling it.
    Signed-off-by: default avatarAndi Kleen <ak@suse.de>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    6e3fbee5
reboot.c 10.6 KB