tcp: make sure EPOLLOUT wont be missed

[ Upstream commit ef8d8ccdc216f797e66cb4a1372f5c4c285ce1e4 ]

As Jason Baron explained in commit 790ba4566c1a ("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: 790ba4566c1a ("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>

diff --git a/net/core/stream.c b/net/core/stream.c
index b96f7a7..3089b01 100644 (file)
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -119,7 +119,6 @@ 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))
@@ -132,11 +131,8 @@ 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);
@@ -168,7 +164,13 @@ out:
 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: