Skip HZ calculation using cfq_slice_async in Linux 4.8+

In task_init() there is a calculation of machdep->hz based on the
value of cfq_slice_async if the symbol exists.

However, kernel commit 9a7f38c42c2b ("cfq-iosched: Convert from
jiffies to nanoseconds") changed the definition of cfq_slice_async
from (HZ / 25) to (NSEC_PER_SEC / 25).  As such, the HZ calculation
will result in a value of 1000000000 for machdep->hz.   In vmcores
where the symbol exists and has this definition, this causes incorrect
results for some calculations.  For a couple of 4.12 vmcores in this
situation crash shows the uptime as 3 seconds, which also throws off
the timestamps in "log -T".

Fix this by skipping the code block for Linux 4.8 and above.

Signed-off-by: Martin Moore <[email protected]>

Author: Moore, Martin (Linux ERT)

task.c

@@ -417,7 +417,8 @@ task_init(void)
 
 	STRUCT_SIZE_INIT(cputime_t, "cputime_t");
 
-	if (symbol_exists("cfq_slice_async")) {
+	if ((THIS_KERNEL_VERSION < LINUX(4,8,0)) &&
+	    symbol_exists("cfq_slice_async")) {
 		uint cfq_slice_async;
 
 		get_symbol_data("cfq_slice_async", sizeof(int),