x86/mce: Fix CMCI preemption bugs

x86/mce: Fix CMCI preemption bugs

The following commit:

  27f6c573e0f7 ("x86, CMCI: Add proper detection of end of CMCI storms")

Added two preemption bugs:

 - machine_check_poll() does a get_cpu_var() without a matching
   put_cpu_var(), which causes preemption imbalance and crashes upon
   bootup.

 - it does percpu ops without disabling preemption. Preemption is not
   disabled due to the mistaken use of a raw spinlock.

To fix these bugs fix the imbalance and change
cmci_discover_lock to a regular spinlock.

Reported-by: Owen Kibel <[email protected]>
Reported-by: Linus Torvalds <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Chen, Gong <[email protected]>
Cc: Josh Boyer <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Alexander Todorov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
--
 arch/x86/kernel/cpu/mcheck/mce.c       |    4 +---
 arch/x86/kernel/cpu/mcheck/mce_intel.c |   18 +++++++++---------
 2 files changed, 10 insertions(+), 12 deletions(-)