From 8b7d7227881269339aabd92cd7d96b8b59a231df Mon Sep 17 00:00:00 2001
From: Casey Bodley <cbodley@redhat.com>
Date: Fri, 9 Sep 2016 16:46:54 -0400
Subject: [PATCH] rgw: detect and work around a curl_multi_wait bug

Fixes: http://tracker.ceph.com/issues/15915
Fixes: http://tracker.ceph.com/issues/16695

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 0359be62b79857357f6d0d4fb81c6bb4e0c381a6)
---
 src/rgw/rgw_http_client.cc | 74 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 72 insertions(+), 2 deletions(-)

diff --git a/src/rgw/rgw_http_client.cc b/src/rgw/rgw_http_client.cc
index 2fa5c91140bca..1dc577d59a39e 100644
--- a/src/rgw/rgw_http_client.cc
+++ b/src/rgw/rgw_http_client.cc
@@ -347,7 +347,8 @@ RGWHTTPClient::~RGWHTTPClient()
 static int clear_signal(int fd)
 {
   // since we're in non-blocking mode, we can try to read a lot more than
-  // one signal from signal_thread() to avoid later wakeups
+  // one signal from signal_thread() to avoid later wakeups. non-blocking reads
+  // are also required to support the curl_multi_wait bug workaround
   std::array<char, 256> buf;
   int ret = ::read(fd, (void *)buf.data(), buf.size());
   if (ret < 0) {
@@ -359,6 +360,67 @@ static int clear_signal(int fd)
 
 #if HAVE_CURL_MULTI_WAIT
 
+static std::once_flag detect_flag;
+static bool curl_multi_wait_bug_present = false;
+
+static int detect_curl_multi_wait_bug(CephContext *cct, CURLM *handle,
+                                      int write_fd, int read_fd)
+{
+  int ret = 0;
+
+  // write to write_fd so that read_fd becomes readable
+  uint32_t buf = 0;
+  ret = ::write(write_fd, &buf, sizeof(buf));
+  if (ret < 0) {
+    ret = -errno;
+    ldout(cct, 0) << "ERROR: " << __func__ << "(): write() returned " << ret << dendl;
+    return ret;
+  }
+
+  // pass read_fd in extra_fds for curl_multi_wait()
+  int num_fds;
+  struct curl_waitfd wait_fd;
+
+  wait_fd.fd = read_fd;
+  wait_fd.events = CURL_WAIT_POLLIN;
+  wait_fd.revents = 0;
+
+  ret = curl_multi_wait(handle, &wait_fd, 1, 0, &num_fds);
+  if (ret != CURLM_OK) {
+    ldout(cct, 0) << "ERROR: curl_multi_wait() returned " << ret << dendl;
+    return -EIO;
+  }
+
+  // curl_multi_wait should flag revents when extra_fd is readable. if it
+  // doesn't, the bug is present and we can't rely on revents
+  if (wait_fd.revents == 0) {
+    curl_multi_wait_bug_present = true;
+    ldout(cct, 0) << "WARNING: detected a version of libcurl which contains a "
+        "bug in curl_multi_wait(). enabling a workaround that may degrade "
+        "performance slightly. please upgrade to a more recent version of "
+        "libcurl." << dendl;
+  }
+
+  return clear_signal(read_fd);
+}
+
+static bool is_signaled(const curl_waitfd& wait_fd)
+{
+  if (wait_fd.fd < 0) {
+    // no fd to signal
+    return false;
+  }
+
+  if (curl_multi_wait_bug_present) {
+    // we can't rely on revents, so we always return true if a wait_fd is given.
+    // this means we'll be trying a non-blocking read on this fd every time that
+    // curl_multi_wait() wakes up
+    return true;
+  }
+
+  return wait_fd.revents > 0;
+}
+
 static int do_curl_wait(CephContext *cct, CURLM *handle, int signal_fd)
 {
   int num_fds;
@@ -374,7 +436,7 @@ static int do_curl_wait(CephContext *cct, CURLM *handle, int signal_fd)
     return -EIO;
   }
 
-  if (wait_fd.revents > 0) {
+  if (is_signaled(wait_fd)) {
     ret = clear_signal(signal_fd);
     if (ret < 0) {
       ldout(cct, 0) << "ERROR: " << __func__ << "(): read() returned " << ret << dendl;
@@ -736,6 +798,14 @@ int RGWHTTPManager::set_threaded()
     return r;
   }
 
+#ifdef HAVE_CURL_MULTI_WAIT
+  // on first initialization, use this pipe to detect whether we're using a
+  // buggy version of libcurl
+  std::call_once(detect_flag, detect_curl_multi_wait_bug, cct,
+                 static_cast<CURLM*>(multi_handle),
+                 thread_pipe[1], thread_pipe[0]);
+#endif
+
   is_threaded = true;
   reqs_thread = new ReqsThread(this);
   reqs_thread->create("http_manager");
-- 
2.39.5