From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Miller" Subject: Re: send(), sendmsg(), sendto() not thread-safe Date: Mon, 15 May 2006 15:49:39 -0700 (PDT) Message-ID: <20060515.154939.28171388.davem@davemloft.net> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org Return-path: Received: from dsl027-180-168.sfo1.dsl.speakeasy.net ([216.27.180.168]:9617 "EHLO sunset.davemloft.net") by vger.kernel.org with ESMTP id S1750708AbWEOWtn (ORCPT ); Mon, 15 May 2006 18:49:43 -0400 To: mark1smi@us.ibm.com In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Mark A Smith Date: Mon, 15 May 2006 14:39:06 -0700 > I discovered that in some cases, send(), sendmsg(), and sendto() are not > thread-safe. Although the man page for these functions does not specify > whether these functions are supposed to be thread-safe, my reading of the > POSIX/SUSv3 specification tells me that they should be. I traced the > problem to tcp_sendmsg(). I was very curious about this issue, so I wrote > up a small page to describe in more detail my findings. You can find it at: > http://www.almaden.ibm.com/cs/people/marksmith/sendmsg.html . I don't understand why the desire is so high to ensure that individual threads get "atomic" writes, you can't even ensure that in the general case. Only sloppy programs that don't do their own internal locking hit into issues in this area. >>From your findings, the vast majority of systems you investigated do not provide "atomic" thread safe write semantics over TCP sockets. And frankly, BSD defines BSD socket semantics here not some wording in the POSIX standards. Finally, this discussion belongs on the networking development mailing list, netdev@vger.kernel.org, not linux-kernel.