x86/pkeys/selftests: Fix protection keys write() warning

write() is marked as having a must-check return value.  Check it and
abort if we fail to write an error message from a signal handler.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171111001232.94813E58@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/testing/selftests/x86/pkey-helpers.h

@@ -30,6 +30,7 @@ static inline void sigsafe_printf(const char *format, ...)
 	if (!dprint_in_signal) {
 		vprintf(format, ap);
 	} else {
+		int ret;
 		int len = vsnprintf(dprint_in_signal_buffer,
 				    DPRINT_IN_SIGNAL_BUF_SIZE,
 				    format, ap);
@@ -39,7 +40,9 @@ static inline void sigsafe_printf(const char *format, ...)
 		 */
 		if (len > DPRINT_IN_SIGNAL_BUF_SIZE)
 			len = DPRINT_IN_SIGNAL_BUF_SIZE;
-		write(1, dprint_in_signal_buffer, len);
+		ret = write(1, dprint_in_signal_buffer, len);
+		if (ret < 0)
+			abort();
 	}
 	va_end(ap);
 }