kgdbts: fix hw_access_break_test

The test for access watchpoints (hw_access_break_test) was broken
(always failed) because the compiler optimized out the write to the
static helper variable (hw_break_val2), as it is never read anywhere.
This resulted in the target variable (hw_break_val) not being accessed
and thus the breakpoint not being triggered.

Remove the helper variable (hw_break_val2), and use READ_ONCE to force
reading the target variable (hw_break_val).

Signed-off-by: Florian Rommel <[e-mail]>
Reviewed-by: Douglas Anderson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/kgdbts.c

···
 #include <linux/kallsyms.h>
 
 #include <asm/sections.h>
+#include <asm/rwonce.h>
 
 #define v1printk(a...) do {		\
 	if (verbose)			\
···
 static int force_hwbrks;
 static int hwbreaks_ok;
 static int hw_break_val;
-static int hw_break_val2;
 static int cont_instead_of_sstep;
 static unsigned long cont_thread_id;
 static unsigned long sstep_thread_id;
···
 
 static void hw_break_val_access(void)
 {
-	hw_break_val2 = hw_break_val;
+	READ_ONCE(hw_break_val);
 }
 
 static void hw_break_val_write(void)