• Ingo Molnar's avatar
    [PATCH] i386/x86_64: ACPI cpu_idle_wait() fix · dc1829a4
    Ingo Molnar authored
    The scheduler on Andreas Friedrich's hyperthreading system stopped
    working properly: the scheduler would never move tasks to another CPU!
    The lask known working kernel was 2.6.8.
    
    After a couple of attempts to corner the bug, the following smoking gun
    was found:
    
      BIOS reported wrong ACPI idfor the processor
      CPU#1: set_cpus_allowed(), swapper:1, 3 -> 2
       [<c0103bbe>] show_trace_log_lvl+0x34/0x4a
       [<c0103ceb>] show_trace+0x2c/0x2e
       [<c01045f8>] dump_stack+0x2b/0x2d
       [<c0116a77>] set_cpus_allowed+0x52/0xec
       [<c0101d86>] cpu_idle_wait+0x2e/0x100
       [<c0259c57>] acpi_processor_power_exit+0x45/0x58
       [<c0259752>] acpi_processor_remove+0x46/0xea
       [<c025c6fb>] acpi_start_single_object+0x47/0x54
       [<c025cee5>] acpi_bus_register_driver+0xa4/0xd3
       [<c04ab2d7>] acpi_processor_init+0x57/0x77
       [<c01004d7>] init+0x146/0x2fd
       [<c0103a87>] kernel_thread_helper+0x7/0x10
    
    a quick look at cpu_idle_wait() shows how broken that code is
    on i386: it changes the init task's affinity map but never
    restores it ...
    
    and because all userspace tasks get forked by init, they all
    inherited that single-CPU affinity mask. x86_64 cloned this
    bug too.
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    Cc: Andreas Friedrich <andreas.friedrich@fujitsu-siemens.com>
    Cc: Wolfgang Erig <Wolfgang.Erig@fujitsu-siemens.com>
    Cc: Andrew Morton <akpm@osdl.org>
    Cc: Adrian Bunk <bunk@stusta.de>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    dc1829a4
process.c 20.8 KB