smp: Iterate functions through llist_for_each_entry_safe()

The IPI function llist iteration is open coded. Lets simplify this
with using an llist iterator.

Also we want to keep the iteration safe against possible
csd.llist->next value reuse from the IPI handler. At least the block
subsystem used to do such things so lets stay careful and use
llist_for_each_entry_safe().
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

kernel/smp.c

@@ -151,7 +151,8 @@ static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
  */
 void generic_smp_call_function_single_interrupt(void)
 {
-	struct llist_node *entry, *next;
+	struct llist_node *entry;
+	struct call_single_data *csd, *csd_next;
 
 	/*
 	 * Shouldn't receive this interrupt on a cpu that is not yet online.
@@ -161,16 +162,9 @@ void generic_smp_call_function_single_interrupt(void)
 	entry = llist_del_all(&__get_cpu_var(call_single_queue));
 	entry = llist_reverse_order(entry);
 
-	while (entry) {
-		struct call_single_data *csd;
-
-		next = entry->next;
-
-		csd = llist_entry(entry, struct call_single_data, llist);
+	llist_for_each_entry_safe(csd, csd_next, entry, llist) {
 		csd->func(csd->info);
 		csd_unlock(csd);
-
-		entry = next;
 	}
 }