x86/dumpstack: Fix occasionally missing registers

If two consecutive stack frames have pt_regs, the oops dump code fails
to print the second frame's registers. Fix that.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Fixes: 3b3fa11bc700 ("x86/dumpstack: Print any pt_regs found on the stack")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/dumpstack.c

···
 		if (stack_name)
 			printk("%s <%s>\n", log_lvl, stack_name);
 
+		if (regs && on_stack(&stack_info, regs, sizeof(*regs)))
+			__show_regs(regs, 0);
+
 		/*
 		 * Scan the stack, printing any text addresses we find.  At the
 		 * same time, follow proper stack frames with the unwinder.
···
 			 * Don't print regs->ip again if it was already printed
 			 * by __show_regs() below.
 			 */
-			if (regs && stack == &regs->ip) {
-				unwind_next_frame(&state);
-				continue;
-			}
+			if (regs && stack == &regs->ip)
+				goto next;
 
 			if (stack == ret_addr_p)
 				reliable = 1;
···
 			if (!reliable)
 				continue;
 
+next:
 			/*
 			 * Get the next frame from the unwinder.  No need to
 			 * check for an error: if anything goes wrong, the rest
···
 
 			/* if the frame has entry regs, print them */
 			regs = unwind_get_entry_regs(&state);
-			if (regs)
+			if (regs && on_stack(&stack_info, regs, sizeof(*regs)))
 				__show_regs(regs, 0);
 		}