Currently printk isn't synchronized except at the byte output level,
leading to interleaving of messages on SMP systems that try to log
simultaneously. This is actually fairly amusing, and actually helpful
occasionally to validate inter-CPU contention down to the "few cycles"
level.
Still, when you're printing data you need to read, you need to be able
to read it. Put a spinlock around each buffered line. This has to
happen in a few places, as there are three different code paths taken
for !USERSPACE, syscall, and user mode.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
3f9ad86b1d