Re: [dpdk-dev] [PATCH] eal_interrupts.c: properly init struct epoll_event (valgrind)

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 12 Feb 2016 22:41:18 -0800
Matthew Hall <mhall@mhcomputing.net> wrote:

> Signed-off-by: Matthew Hall <mhall@mhcomputing.net>
> ---
>  lib/librte_eal/linuxapp/eal/eal_interrupts.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/librte_eal/linuxapp/eal/eal_interrupts.c b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
> index 06b26a9..b33ccdb 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_interrupts.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
> @@ -800,6 +800,7 @@ static __attribute__((noreturn)) void *
>  eal_intr_thread_main(__rte_unused void *arg)
>  {
>  	struct epoll_event ev;
> +	memset(&ev, 0, sizeof(ev));
>  
>  	/* host thread, never break out */
>  	for (;;) {

I wonder why valgrind is giving this false report.
The only place this data structure is used is here, and all fields
in epoll_event are correctly set.

		TAILQ_FOREACH(src, &intr_sources, next) {
			if (src->callbacks.tqh_first == NULL)
				continue; /* skip those with no callbacks */
			ev.events = EPOLLIN | EPOLLPRI;
			ev.data.fd = src->intr_handle.fd;

			/**
			 * add all the uio device file descriptor
			 * into wait list.
			 */
			if (epoll_ctl(pfd, EPOLL_CTL_ADD,
					src->intr_handle.fd, &ev) < 0){
				rte_panic("Error adding fd %d epoll_ctl, %s\n",
					src->intr_handle.fd, strerror(errno));

A better patch would be to move the data structure into the
code block used, and get rid of the useless else (rte_panic never returns);
and fix the indentation, and use C99 initialization which should make valgrind
happier.

The moral is don't just slap memsets around

diff --git a/lib/librte_eal/linuxapp/eal/eal_interrupts.c b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
index 06b26a9..d53826e 100644
--- a/lib/librte_eal/linuxapp/eal/eal_interrupts.c
+++ b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
@@ -799,8 +799,6 @@ eal_intr_handle_interrupts(int pfd, unsigned totalfds)
 static __attribute__((noreturn)) void *
 eal_intr_thread_main(__rte_unused void *arg)
 {
-	struct epoll_event ev;
-
 	/* host thread, never break out */
 	for (;;) {
 		/* build up the epoll fd with all descriptors we are to
@@ -834,20 +832,22 @@ eal_intr_thread_main(__rte_unused void *arg)
 		TAILQ_FOREACH(src, &intr_sources, next) {
 			if (src->callbacks.tqh_first == NULL)
 				continue; /* skip those with no callbacks */
-			ev.events = EPOLLIN | EPOLLPRI;
-			ev.data.fd = src->intr_handle.fd;
+
+			struct epoll_event ev = {
+				.events = EPOLLIN | EPOLLPRI,
+				.data.fd = src->intr_handle.fd,
+			};
 
 			/**
 			 * add all the uio device file descriptor
 			 * into wait list.
 			 */
 			if (epoll_ctl(pfd, EPOLL_CTL_ADD,
-					src->intr_handle.fd, &ev) < 0){
+					src->intr_handle.fd, &ev) < 0)
 				rte_panic("Error adding fd %d epoll_ctl, %s\n",
 					src->intr_handle.fd, strerror(errno));
-			}
-			else
-				numfds++;
+
+			numfds++;
 		}
 		rte_spinlock_unlock(&intr_lock);
 		/* serve the interrupt */