Commit fda20929 authored Aug 16, 2019 by Eric Dumazet Committed by Greg Kroah-Hartman Sep 06, 2019

tcp: make sure EPOLLOUT wont be missed



[ Upstream commit ef8d8ccdc216f797e66cb4a1372f5c4c285ce1e4 ]

As Jason Baron explained in commit 790ba456 ("tcp: set SOCK_NOSPACE
under memory pressure"), it is crucial we properly set SOCK_NOSPACE
when needed.

However, Jason patch had a bug, because the 'nonblocking' status
as far as sk_stream_wait_memory() is concerned is governed
by MSG_DONTWAIT flag passed at sendmsg() time :

    long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);

So it is very possible that tcp sendmsg() calls sk_stream_wait_memory(),
and that sk_stream_wait_memory() returns -EAGAIN with SOCK_NOSPACE
cleared, if sk->sk_sndtimeo has been set to a small (but not zero)
value.

This patch removes the 'noblock' variable since we must always
set SOCK_NOSPACE if -EAGAIN is returned.

It also renames the do_nonblock label since we might reach this
code path even if we were in blocking mode.

Fixes: 790ba456 ("tcp: set SOCK_NOSPACE under memory pressure")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jason Baron <jbaron@akamai.com>
Reported-by: Vladimir Rutsky <rutsky@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 53856af7

net/core/stream.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -118,7 +118,6 @@ int sk_stream_wait_memory(struct sock sk, long timeo_p)
		int err = 0;
		long vm_wait = 0;
		long current_timeo = *timeo_p;
		bool noblock = (*timeo_p ? false : true);
		DEFINE_WAIT(wait);

		if (sk_stream_memory_free(sk))
		@@ -131,11 +130,8 @@ int sk_stream_wait_memory(struct sock sk, long timeo_p)

		if (sk->sk_err \|\| (sk->sk_shutdown & SEND_SHUTDOWN))
		goto do_error;
		if (!*timeo_p) {
		if (noblock)
		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
		goto do_nonblock;
		}
		if (!*timeo_p)
		goto do_eagain;
		if (signal_pending(current))
		goto do_interrupted;
		sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
		@@ -167,7 +163,13 @@ int sk_stream_wait_memory(struct sock sk, long timeo_p)
		do_error:
		err = -EPIPE;
		goto out;
		do_nonblock:
		do_eagain:
		/* Make sure that whenever EAGAIN is returned, EPOLLOUT event can
		* be generated later.
		* When TCP receives ACK packets that make room, tcp_check_space()
		* only calls tcp_new_space() if SOCK_NOSPACE is set.
		*/
		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
		err = -EAGAIN;
		goto out;
		do_interrupted: