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![]() Applications use -ECONNREFUSED as returned from write() in order to determine that a socket should be closed. However, when using connected dgram unix sockets in a poll/write loop, a final POLLOUT event can be missed when the remote end closes. Thus, the poll is stuck forever: thread 1 (client) thread 2 (server) connect() to server write() returns -EAGAIN unix_dgram_poll() -> unix_recvq_full() is true close() ->unix_release_sock() ->wake_up_interruptible_all() unix_dgram_poll() (due to the wake_up_interruptible_all) -> unix_recvq_full() still is true ->free all skbs Now thread 1 is stuck and will not receive anymore wakeups. In this case, when thread 1 gets the -EAGAIN, it has not queued any skbs otherwise the 'free all skbs' step would in fact cause a wakeup and a POLLOUT return. So the race here is probably fairly rare because it means there are no skbs that thread 1 queued and that thread 1 schedules before the 'free all skbs' step. This issue was reported as a hang when /dev/log is closed. The fix is to signal POLLOUT if the socket is marked as SOCK_DEAD, which means a subsequent write() will get -ECONNREFUSED. Reported-by: Ian Lance Taylor <iant@golang.org> Cc: David Rientjes <rientjes@google.com> Cc: Rainer Weikusat <rweikusat@mobileactivedefense.com> Cc: Eric Dumazet <edumazet@google.com> Signed-off-by: Jason Baron <jbaron@akamai.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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af_unix.c | ||
diag.c | ||
garbage.c | ||
Kconfig | ||
Makefile | ||
sysctl_net_unix.c |