• KOSAKI Motohiro's avatar
    tcp: select(writefds) don't hang up when a peer close connection · d84ba638
    KOSAKI Motohiro authored
    This issue come from ruby language community. Below test program
    hang up when only run on Linux.
    
    	% uname -mrsv
    	Linux 2.6.26-2-486 #1 Sat Dec 26 08:37:39 UTC 2009 i686
    	% ruby -rsocket -ve '
    	BasicSocket.do_not_reverse_lookup = true
    	serv = TCPServer.open("127.0.0.1", 0)
    	s1 = TCPSocket.open("127.0.0.1", serv.addr[1])
    	s2 = serv.accept
    	s2.close
    	s1.write("a") rescue p $!
    	s1.write("a") rescue p $!
    	Thread.new {
    	  s1.write("a")
    	}.join'
    	ruby 1.9.3dev (2010-07-06 trunk 28554) [i686-linux]
    	#<Errno::EPIPE: Broken pipe>
    	[Hang Here]
    
    FreeBSD, Solaris, Mac doesn't. because Ruby's write() method call
    select() internally. and tcp_poll has a bug.
    
    SUS defined 'ready for writing' of select() as following.
    
    |  A descriptor shall be considered ready for writing when a call to an output
    |  function with O_NONBLOCK clear would not block, whether or not the function
    |  would transfer data successfully.
    
    That said, EPIPE situation is clearly one of 'ready for writing'.
    
    We don't have read-side issue because tcp_poll() already has read side
    shutdown care.
    
    |        if (sk->sk_shutdown & RCV_SHUTDOWN)
    |                mask |= POLLIN | POLLRDNORM | POLLRDHUP;
    
    So, Let's insert same logic in write side.
    
    - reference url
      http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/31065
      http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/31068Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    d84ba638
tcp.c 85.7 KB