[OpenWrt-Devel] [PATCH][RFC] libubus: added max retry mechanism

[Alexandru Ardelean]

Seems that every once in a while libubus takes up the whole CPU
for certain processes.

This could be bad code that I keep (re)writing.

I don't know if it's ok to give up after a certain number of
retries; high CPU usage could indicate I should look deeper
at my logic.

Which is why I've submitted this patch for review/opinions/comments.

Can also be reviewed here:
https://github.com/commodo/ubus/commits/max_retry_mechanism

Thanks

---
 libubus-io.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/libubus-io.c b/libubus-io.c
index 31dad27..6bc06aa 100644
--- a/libubus-io.c
+++ b/libubus-io.c
@@ -29,6 +29,7 @@
 #define STATIC_IOV(_var) { .iov_base = (char *) &(_var), .iov_len = sizeof(_var) }
 
 #define UBUS_MSGBUF_REDUCTION_INTERVAL	16
+#define UBUS_MAX_RETRIES		256
 
 static const struct blob_attr_info ubus_policy[UBUS_ATTR_MAX] = {
 	[UBUS_ATTR_STATUS] = { .type = BLOB_ATTR_INT32 },
@@ -75,6 +76,7 @@ static int writev_retry(int fd, struct iovec *iov, int iov_len, int sock_fd)
 		.msg_controllen = sizeof(fd_buf),
 	};
 	int len = 0;
+	int retries = UBUS_MAX_RETRIES;
 
 	do {
 		int cur_len;
@@ -91,9 +93,9 @@ static int writev_retry(int fd, struct iovec *iov, int iov_len, int sock_fd)
 			switch(errno) {
 			case EAGAIN:
 				wait_data(fd, true);
-				break;
 			case EINTR:
-				break;
+				if (retries-- > 0)
+					break;
 			default:
 				return -1;
 			}
@@ -115,6 +117,7 @@ static int writev_retry(int fd, struct iovec *iov, int iov_len, int sock_fd)
 		iov->iov_len -= cur_len;
 		msghdr.msg_iov = iov;
 		msghdr.msg_iovlen = iov_len;
+		retries = UBUS_MAX_RETRIES;
 	} while (1);
 
 	/* Should never reach here */
@@ -170,6 +173,7 @@ static int recv_retry(int fd, struct iovec *iov, bool wait, int *recv_fd)
 		.msg_iov = iov,
 		.msg_iovlen = 1,
 	};
+	int retries = UBUS_MAX_RETRIES;
 
 	while (iov->iov_len > 0) {
 		if (wait)
@@ -192,11 +196,16 @@ static int recv_retry(int fd, struct iovec *iov, bool wait, int *recv_fd)
 			bytes = 0;
 			if (uloop_cancelled)
 				return 0;
-			if (errno == EINTR)
-				continue;
-
-			if (errno != EAGAIN)
+			switch (errno) {
+			case EINTR:
+				if (retries-- > 0)
+					continue;
+			case EAGAIN:
+				if (retries-- > 0)
+					break;
+			default:
 				return -1;
+			}
 		}
 		if (!wait && !bytes)
 			return 0;
@@ -210,6 +219,7 @@ static int recv_retry(int fd, struct iovec *iov, bool wait, int *recv_fd)
 		iov->iov_len -= bytes;
 		iov->iov_base += bytes;
 		total += bytes;
+		retries = UBUS_MAX_RETRIES;
 	}
 
 	return total;
-- 
1.8.4.5
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