crimson/osd: fix the lifetime of Notify during timeouts.

This fixes a segfault during `LibRadosWatchNotify.WatchNotify2Timeout`.

Signed-off-by: Radoslaw Zarzynski <[email protected]>

src/crimson/osd/watch.cc

@@ -210,6 +210,10 @@ void Notify::do_timeout()
   if (complete) {
     return;
   }
+  // it might be that `this` is kept alive only because of the reference
+  // a watcher stores and which is being removed by `cancel_notify()`.
+  // to avoid use-after-free we bump up the ref counter with `guard_ptr`.
+  [[maybe_unused]] auto guard_ptr = shared_from_this();
   for (auto& watcher : watchers) {
     watcher->cancel_notify(ninfo.notify_id);
   }

src/crimson/osd/watch.h

@@ -106,7 +106,7 @@ struct notify_reply_t {
 };
 std::ostream &operator<<(std::ostream &out, const notify_reply_t &rhs);
 
-class Notify {
+class Notify : public seastar::enable_shared_from_this<Notify> {
   std::set<WatchRef> watchers;
   const notify_info_t ninfo;
   crimson::net::ConnectionRef conn;