x86/stacktrace: Do not unwind after user regs

Josh pointed out, that there is no way a frame can be after user regs.
So remove the last unwind and the check.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/lkml/20180518064713.26440-1-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/stacktrace.c

@@ -113,15 +113,6 @@ __save_stack_trace_reliable(struct stack_trace *trace,
 			if (!user_mode(regs))
 				return -EINVAL;
 
-			/*
-			 * The last frame contains the user mode syscall
-			 * pt_regs.  Skip it and finish the unwind.
-			 */
-			unwind_next_frame(&state);
-			if (!unwind_done(&state)) {
-				STACKTRACE_DUMP_ONCE(task);
-				return -EINVAL;
-			}
 			break;
 		}