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Miller" Cc: netdev , Soheil Hassas Yeganeh , Neal Cardwell , Eric Dumazet , Vladimir Rutsky References: <20190817042622.91497-1-edumazet@google.com> From: Jason Baron Message-ID: Date: Sat, 17 Aug 2019 10:19:51 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190817042622.91497-1-edumazet@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-17_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908170154 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:5.22.84,1.0.8 definitions=2019-08-17_06:2019-08-16,2019-08-17 signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 mlxlogscore=999 clxscore=1011 phishscore=0 bulkscore=0 spamscore=0 adultscore=0 lowpriorityscore=0 suspectscore=2 malwarescore=0 impostorscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1906280000 definitions=main-1908170154 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 8/17/19 12:26 AM, Eric Dumazet wrote: > 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. Is MSG_DONTWAIT not set in this case? The original patch was intended only for the explicit non-blocking case. The epoll manpage says: "EPOLLET flag should use nonblocking file descriptors". So the original intention was not to impact the blocking case. This seems to me like a different use-case. Thanks, -Jason > 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 > Cc: Jason Baron > Reported-by: Vladimir Rutsky > --- > net/core/stream.c | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > > diff --git a/net/core/stream.c b/net/core/stream.c > index e94bb02a56295ec2db34ab423a8c7c890df0a696..4f1d4aa5fb38d989a9c81f32dfce3f31bbc1fa47 100644 > --- a/net/core/stream.c > +++ b/net/core/stream.c > @@ -120,7 +120,6 @@ 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_FUNC(wait, woken_wake_function); > > if (sk_stream_memory_free(sk)) > @@ -133,11 +132,8 @@ 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); > @@ -169,7 +165,13 @@ 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: >