Commit f56e8a076 "x86/mce: Fix RCU lockdep splats" introduced the
following build bug:
arch/x86/kernel/cpu/mcheck/mce.c: In function 'mce_log':
arch/x86/kernel/cpu/mcheck/mce.c:166: error: 'mce_read_mutex' undeclared (first use in this function)
arch/x86/kernel/cpu/mcheck/mce.c:166: error: (Each undeclared identifier is reported only once
arch/x86/kernel/cpu/mcheck/mce.c:166: error: for each function it appears in.)
Move the in-the-middle-of-file lock variable up to the variable
definition section, the top of the .c file.