epoll reporting events when it hasn't been asked to

Ben
2004-04-01T16:54:47Z

Hi,

epoll seems to behave oddly with TCP sockets that return ECONNRESET on a
read. Here's an abridged strace snippet:
(my strace doesn't cope very well with epoll syscalls, so I've mixed in
some of the program's debug output as well)

epoll_create(0x400) = 5

...

socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 10
setsockopt(10, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(10, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
bind(10, {sa_family=AF_INET, sin_port=htons(2342), sin_addr=inet_addr("10.100.1.208")}, 16) = 0

EPollMultiplexer::Add( fd 10 events 1 )
epoll_ctl(0x5, 0x1, 0xa, 0xbffff010) = 0

EPollMultiplexer::Poll()
epoll_wait(0x5, 0x831b390, 0x20, 0x3e8) = 1
fd 10 has events 1

accept(10, {sa_family=AF_INET, sin_port=htons(47255), sin_addr=inet_addr("10.100.1.208")}, [16]) = 7

EPollMultiplexer::Add( fd 7 events 1 )
epoll_ctl(0x5, 0x1, 0x7, 0xbffff5c0) = 0

socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 11
connect(11, {sa_family=AF_INET, sin_port=htons(21), sin_addr=inet_addr("10.100.1.5")}, 16) = -1 EINPROGRESS (Operation now in progress)

EPollMultiplexer::Add( fd 11 events 1 )
epoll_ctl(0x5, 0x1, 0xb, 0xbffff3f0) = 0

EPollMultiplexer::Poll()
epoll_wait(0x5, 0x831b390, 0x20, 0x3e8) = 1
fd 11 has events 1

EPollMultiplexer::Poll()
epoll_wait(0x5, 0x831b390, 0x20, 0x3e8) = 2
fd 10 has events 1
fd 7 has events 25

read(7, 0x8336240, 4096) = -1 ECONNRESET (Connection reset by peer)

EPollMultiplexer::Poll()
Setting events on fd 7 to 0
epoll_ctl(0x5, 0x3, 0x7, 0x8301550) = 0
epoll_wait(0x5, 0x831b390, 0x20, 0x3e8) = 2
fd 11 has events 1
fd 7 has events 16

This is odd. The epoll_ctl() got rid of all events for FD 7, yet the
epoll_wait() following it returns event 16 (EPOLLHUP). Is this a bug?
I don't normally see this behaviour for most connections, is it perhaps
to do with the read returning ECONNRESET ?

(This is on 2.6.2-rc1-mm1 and on 2.6.5-rc3-mm3, on x86 and x86_64)

Ben