panic, x86: Fix re-entrance problem due to panic on NMI

If panic on NMI happens just after panic() on the same CPU, panic() is
recursively called. Kernel stalls, as a result, after failing to acquire
panic_lock.

To avoid this problem, don't call panic() in NMI context if we've
already entered panic().

For that, introduce nmi_panic() macro to reduce code duplication. In
the case of panic on NMI, don't return from NMI handlers if another CPU
already panicked.

Signed-off-by: Hidehiro Kawai <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Aaron Tomlin <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Gobinda Charan Maji <[email protected]>
Cc: HATAYAMA Daisuke <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Javi Merino <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: lkml <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Michal Nazarewicz <[email protected]>
Cc: Nicolas Iooss <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Vivek Goyal <[email protected]>
Link: http://lkml.kernel.org/r/20151210014626.25437.13302.stgit@softrs
[ Cleanup comments, fixup formatting. ]
Signed-off-by: Borislav Petkov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>

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