[PATCH lttng-tools 5/8] Fix hang in thread_rotation when using compat-poll

From: Yannick Lamarre <ylamarre@efficios.com>
To: lttng-dev@lists.lttng.org
Cc: jgalar@efficios.com
Subject: [PATCH lttng-tools 5/8] Fix hang in thread_rotation when using compat-poll
Date: Tue, 19 Mar 2019 17:17:32 -0400	[thread overview]
Message-ID: <20190319211735.7187-6-ylamarre__49749.0754861914$1553030379$gmane$org@efficios.com> (raw)
In-Reply-To: <20190319211735.7187-1-ylamarre@efficios.com>

The poll flavor of the lttng_poll api requires the caller to verify
which of the fd has really waken the thread from wait. This
verification was missing and a blocking read was made on an empty fd.

Signed-off-by: Yannick Lamarre <ylamarre@efficios.com>
---
 src/bin/lttng-sessiond/rotation-thread.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/bin/lttng-sessiond/rotation-thread.c b/src/bin/lttng-sessiond/rotation-thread.c
index 6669372d..b86b1668 100644
--- a/src/bin/lttng-sessiond/rotation-thread.c
+++ b/src/bin/lttng-sessiond/rotation-thread.c
@@ -974,6 +974,10 @@ void *thread_rotation(void *data)
 			int fd = LTTNG_POLL_GETFD(&thread.events, i);
 			uint32_t revents = LTTNG_POLL_GETEV(&thread.events, i);
 
+			if (!revents) {
+				/* No activity for this FD (poll implementation). */
+				continue;
+			}
 			DBG("[rotation-thread] Handling fd (%i) activity (%u)",
 					fd, revents);
 
-- 
2.11.0
