Re: 100% CPU usage

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? :)

-- Pasi


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