• Konrad Rzeszutek Wilk's avatar
    x86/microcode: Add local mutex to fix physical CPU hot-add deadlock · 903bded0
    Konrad Rzeszutek Wilk authored
    commit 074d72ff upstream.
    
    This can easily be triggered if a new CPU is added (via
    ACPI hotplug mechanism) and from user-space you do:
    
       echo 1 > /sys/devices/system/cpu/cpu3/online
    
    (or wait for UDEV to do it) on a newly appeared physical CPU.
    
    The deadlock is that the "store_online" in drivers/base/cpu.c
    takes the cpu_hotplug_driver_lock() lock, then calls "cpu_up".
    "cpu_up" eventually ends up calling "save_mc_for_early"
    which also takes the cpu_hotplug_driver_lock() lock.
    
    And here is that lockdep thinks of it:
    
     smpboot: Stack at about ffff880075c39f44
     smpboot: CPU3: has booted.
     microcode: CPU3 sig=0x206a7, pf=0x2, revision=0x25
    
     =============================================
     [ INFO: possible recursive locking detected ]
     3.9.0upstream-10129-g167af0e #1 Not tainted
     ---------------------------------------------
     sh/2487 is trying to acquire lock:
      (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>] cpu_hotplug_driver_lock+0x12/0x20
    
     but task is already holding lock:
      (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>] cpu_hotplug_driver_lock+0x12/0x20
    
     other info that might help us debug this:
      Possible unsafe locking scenario:
    
            CPU0
            ----
       lock(x86_cpu_hotplug_driver_mutex);
       lock(x86_cpu_hotplug_driver_mutex);
    
      *** DEADLOCK ***
    
      May be due to missing lock nesting notation
    
     6 locks held by sh/2487:
      #0:  (sb_writers#5){.+.+.+}, at: [<ffffffff811ca48d>] vfs_write+0x17d/0x190
      #1:  (&buffer->mutex){+.+.+.}, at: [<ffffffff812464ef>] sysfs_write_file+0x3f/0x160
      #2:  (s_active#20){.+.+.+}, at: [<ffffffff81246578>] sysfs_write_file+0xc8/0x160
      #3:  (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>] cpu_hotplug_driver_lock+0x12/0x20
      #4:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff810961c2>] cpu_maps_update_begin+0x12/0x20
      #5:  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff810962a7>] cpu_hotplug_begin+0x27/0x60
    Suggested-and-Acked-by: default avatarBorislav Petkov <bp@alien8.de>
    Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: fenghua.yu@intel.com
    Cc: xen-devel@lists.xensource.com
    Link: http://lkml.kernel.org/r/1368029583-23337-1-git-send-email-konrad.wilk@oracle.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    903bded0
microcode_intel_early.c 19.5 KB