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x86/microcode: Add local mutex to fix physical CPU hot-add deadlock 

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: Borislav Petkov <bp@alien8.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: fenghua.yu@intel.com
Cc: xen-devel@lists.xensource.com
Cc: stable@vger.kernel.org # for v3.9
Link: http://lkml.kernel.org/r/1368029583-23337-1-git-send-email-konrad.wilk@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Konrad Rzeszutek Wilk 2013-05-08 12:13:03 -04:00 committed by Ingo Molnar
parent 97a5b81fa4
commit 074d72ff57
1 changed files with 3 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/kernel/microcode_intel_early.c
View File

@ -487,6 +487,7 @@ static inline void show_saved_mc(void)
#endif
#if defined(CONFIG_MICROCODE_INTEL_EARLY) && defined(CONFIG_HOTPLUG_CPU)
static DEFINE_MUTEX(x86_cpu_microcode_mutex);
/*
* Save this mc into mc_saved_data. So it will be loaded early when a CPU is
* hot added or resumes.
@ -507,7 +508,7 @@ int save_mc_for_early(u8 *mc)
* Hold hotplug lock so mc_saved_data is not accessed by a CPU in
* hotplug.
*/
cpu_hotplug_driver_lock();
mutex_lock(&x86_cpu_microcode_mutex);
mc_saved_count_init = mc_saved_data.mc_saved_count;
mc_saved_count = mc_saved_data.mc_saved_count;
@ -544,7 +545,7 @@ int save_mc_for_early(u8 *mc)
}
out:
cpu_hotplug_driver_unlock();
mutex_unlock(&x86_cpu_microcode_mutex);
return ret;
}