powerpc/fadump: Fix the race in crash_fadump().
There are chances that multiple CPUs can call crash_fadump() simultaneously and would start duplicating same info to vmcoreinfo ELF note section. This causes makedumpfile to fail during kdump capture. One example is, triggering dumprestart from HMC which sends system reset to all the CPUs at once. makedumpfile --dump-dmesg /proc/vmcore read_vmcoreinfo_basic_info: Invalid data in /tmp/vmcoreinfoyjgxlL: CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971 makedumpfile Failed. Running makedumpfile --dump-dmesg /proc/vmcore failed (1). makedumpfile -d 31 -l /proc/vmcore read_vmcoreinfo_basic_info: Invalid data in /tmp/vmcoreinfo1mmVdO: CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971 makedumpfile Failed. Running makedumpfile -d 31 -l /proc/vmcore failed (1). Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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