Re: 100% CPU usage

On Mon, Jun 10, 2013 at 11:59:51AM +0300, Pasi Kärkkäinen wrote:
> On Thu, Jun 06, 2013 at 09:11:15PM +0100, John Sullivan wrote:
> > On Thursday, June 6, 2013, 2:55:25 PM, Graeme Fowler wrote:
> > > It seems that your mail server is the culprit. I don't fully understand why - a couple of messages get out, then a bunch of connectons get stuck:
> > 
> > Not convinced the keepalived smtp engine is right here.
> > 
> > > On 6 Jun 2013, at 12:12, Rimbalza Rimbalza <[email protected]> wrote:
> > >> The log file contains these 3 repeating lines forever.
> > >> 1530  13:08:46.986966 read(14, "", 512) = 0
> > >> 1530  13:08:46.986993 read(13, "", 512) = 0
> > >> 1530  13:08:46.987021 select(1024, [4 6 11 13 14], [], [], {0, 62960}) = 2 (in [13 14], left {0, 62958})
> > >> 1530  13:08:46.987090 read(14, "", 512) = 0
> > >> 1530  13:08:46.987117 read(13, "", 512) = 0
> > >> 1530  13:08:46.987145 select(1024, [4 6 11 13 14], [], [], {0, 62836}) = 2 (in [13 14], left {0, 62834})
> > 
> > Check out keepalived/core/smtp.c, smtp_read_thread().
> > 
> > It does the read, checks for -1 - mostly error conditions except
> > for EAGAIN which, on a non-blocking socket, simply means no data
> > is available *yet* but the socket is still good.
> > 
> > Otherwise it assumes it got some data, appends it to the buffer,
> > parses for the status code etc., requeues the select for read.
> > 
> > At no point does it check for a zero return from read(), which
> > means the socket has been closed by the other end (or otherwise
> > failed). On a closed socket (where all input has already been
> > drained), read() will *always* return immediately with 0, and
> > select() will always indicate readability, hence the spin.
> > 
> 
> Wanna send a patch? :)

I've attached a quick-and-dirty patch. Note that I have not completely
tested this patch because I am unable to easily recreate the
problem. Comments welcome.

Ryan

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diff --git a/keepalived/core/smtp.c b/keepalived/core/smtp.c
index e74a0a5..7bfb5f1 100644
--- a/keepalived/core/smtp.c
+++ b/keepalived/core/smtp.c
@@ -167,8 +167,8 @@ smtp_read_thread(thread_t * thread)
 	rcv_buffer_size = read(thread->u.fd, buffer + smtp->buflen,
 			       SMTP_BUFFER_LENGTH - smtp->buflen);
 
-	if (rcv_buffer_size == -1) {
-		if (errno == EAGAIN)
+	if (rcv_buffer_size <= 0) {
+		if (rcv_buffer_size == -1 && errno == EAGAIN)
 			goto end;
 		log_message(LOG_INFO, "Error reading data from remote SMTP server [%s]:%d."
 				    , inet_sockaddrtos(&global_data->smtp_server), SMTP_PORT);