rgw: don't try to wait for pending if list is empty

Fixes: #8846
Backport: firefly, dumpling

This was broken at ea68b9372319fd0bab40856db26528d36359102e. We ended
up calling wait_pending_front() when pending list was empty.
This commit also moves the need_to_wait check to a different place,
where we actually throttle (and not just drain completed IOs).

Reported-by: Sylvain Munaut <s.munaut@whatever-company.com>
Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
(cherry picked from commit f9f2417d7db01ecf2425039539997901615816a9)

diff --git a/src/rgw/rgw_rados.cc b/src/rgw/rgw_rados.cc
index edde93b4b8ea3e1079e4808b9c43c03a08f19f89..3a15c73918aff676358090a7c1fdaacf324a4e24 100644 (file)
--- a/src/rgw/rgw_rados.cc
+++ b/src/rgw/rgw_rados.cc
@@ -595,6 +595,9 @@ struct put_obj_aio_info RGWPutObjProcessor_Aio::pop_pending()
 
 int RGWPutObjProcessor_Aio::wait_pending_front()
 {
+  if (pending.empty()) {
+    return 0;
+  }
   struct put_obj_aio_info info = pop_pending();
   int ret = store->aio_wait(info.handle);
   return ret;
@@ -628,8 +631,9 @@ int RGWPutObjProcessor_Aio::throttle_data(void *handle, bool need_to_wait)
     pending.push_back(info);
   }
   size_t orig_size = pending.size();
-  while (pending_has_completed()
-         || need_to_wait) {
+
+  /* first drain complete IOs */
+  while (pending_has_completed()) {
     int r = wait_pending_front();
     if (r < 0)
       return r;
@@ -642,10 +646,14 @@ int RGWPutObjProcessor_Aio::throttle_data(void *handle, bool need_to_wait)
     max_chunks++;
   }
 
-  if (pending.size() > max_chunks) {
+  /* now throttle. Note that need_to_wait should only affect the first IO operation */
+  if (pending.size() > max_chunks ||
+      need_to_wait) {
     int r = wait_pending_front();
     if (r < 0)
       return r;
+
+    need_to_wait = false;
   }
   return 0;
 }