stacktrace: Move documentation for arch_stack_walk_reliable() to header

Currently arch_stack_walk_reliable() is documented with an identical
comment in both x86 and S/390 implementations which is a bit redundant.
Move this to the header and convert to kerneldoc while we're at it.

Signed-off-by: Mark Brown <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Reviewed-by: Miroslav Benes <[e-mail]>
Acked-by: Vasily Gorbik <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/s390/kernel/stacktrace.c

···
 	}
 }
 
-/*
- * This function returns an error if it detects any unreliable features of the
- * stack.  Otherwise it guarantees that the stack trace is reliable.
- *
- * If the task is not 'current', the caller *must* ensure the task is inactive.
- */
 int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 			     void *cookie, struct task_struct *task)
 {

arch/x86/kernel/stacktrace.c

···
 	}
 }
 
-/*
- * This function returns an error if it detects any unreliable features of the
- * stack.  Otherwise it guarantees that the stack trace is reliable.
- *
- * If the task is not 'current', the caller *must* ensure the task is inactive.
- */
 int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 			     void *cookie, struct task_struct *task)
 {

include/linux/stacktrace.h

···
  */
 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 		     struct task_struct *task, struct pt_regs *regs);
+
+/**
+ * arch_stack_walk_reliable - Architecture specific function to walk the
+ *			      stack reliably
+ *
+ * @consume_entry:	Callback which is invoked by the architecture code for
+ *			each entry.
+ * @cookie:		Caller supplied pointer which is handed back to
+ *			@consume_entry
+ * @task:		Pointer to a task struct, can be NULL
+ *
+ * This function returns an error if it detects any unreliable
+ * features of the stack. Otherwise it guarantees that the stack
+ * trace is reliable.
+ *
+ * If the task is not 'current', the caller *must* ensure the task is
+ * inactive and its stack is pinned.
+ */
 int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, void *cookie,
 			     struct task_struct *task);
+
 void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
 			  const struct pt_regs *regs);