vcl: improve vpp detached handling for mq epoll apps

Apps that rely on epoll and use eventfds for mq signaling can
potentially sleep indefinitely if vcl detaches from vpp and no libc fd
generates events.

To avoid this, at detach time, force creation of a pair of pipes that
constantly generates mq_epfd events to force apps, including ldp, to
request vppcom epoll_waits which retry attaching to vpp.

Type: improvement

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: Ie2ac338cc10721829e6ac525ee7d6b812354e9a3

1 files changed, 49 insertions, 0 deletions

diff --git a/src/vcl/vcl_private.c b/src/vcl/vcl_private.c
index 6892688da5a..1adc8cb6666 100644
--- a/src/vcl/vcl_private.c
+++ b/src/vcl/vcl_private.c
@@ -189,6 +189,53 @@ vcl_worker_cleanup_cb (void *arg)
 }
 
 void
+vcl_worker_detached_start_signal_mq (vcl_worker_t *wrk)
+{
+  /* Generate mq epfd events using pipes to hopefully force
+   * calls into epoll_wait which retries attaching to vpp */
+  if (!wrk->detached_pipefds[0])
+    {
+      if (pipe (wrk->detached_pipefds))
+	{
+	  VDBG (0, "failed to add mq eventfd to mq epoll fd");
+	  exit (1);
+	}
+    }
+
+  struct epoll_event evt = {};
+  evt.events = EPOLLIN;
+  evt.data.u32 = wrk->detached_pipefds[0];
+  if (epoll_ctl (wrk->mqs_epfd, EPOLL_CTL_ADD, wrk->detached_pipefds[0],
+		 &evt) < 0)
+    {
+      VDBG (0, "failed to add mq eventfd to mq epoll fd");
+      exit (1);
+    }
+
+  int sig = 1, __clib_unused rv;
+  rv = write (wrk->detached_pipefds[1], &sig, 1);
+}
+
+void
+vcl_worker_detached_signal_mq (vcl_worker_t *wrk)
+{
+  int buf, __clib_unused rv;
+  rv = read (wrk->detached_pipefds[0], &buf, 1);
+  rv = write (wrk->detached_pipefds[1], &buf, 1);
+}
+
+void
+vcl_worker_detached_stop_signal_mq (vcl_worker_t *wrk)
+{
+  if (epoll_ctl (wrk->mqs_epfd, EPOLL_CTL_DEL, wrk->detached_pipefds[0], 0) <
+      0)
+    {
+      VDBG (0, "failed to del mq eventfd to mq epoll fd");
+      exit (1);
+    }
+}
+
+void
 vcl_worker_detach_sessions (vcl_worker_t *wrk)
 {
   session_event_t *e;
@@ -239,6 +286,8 @@ vcl_worker_detach_sessions (vcl_worker_t *wrk)
 
   vec_free (seg_indices);
   hash_free (seg_indices_map);
+
+  vcl_worker_detached_start_signal_mq (wrk);
 }
 
 void