From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/13506 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: sem_wait and EINTR Date: Wed, 5 Dec 2018 22:17:56 -0500 Message-ID: <20181206031756.GZ23599@brightrain.aerifal.cx> References: <20181205191605.72492698@orivej.orivej.org> <20181205194759.GA32233@voyager> <20181205212716.sx6ra2xqhuei735q@core.my.home> <20181205215826.GX23599@brightrain.aerifal.cx> <20181206024340.202e0fc4@orivej.orivej.org> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: blaine.gmane.org 1544066165 538 195.159.176.226 (6 Dec 2018 03:16:05 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 6 Dec 2018 03:16:05 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-13522-gllmg-musl=m.gmane.org@lists.openwall.com Thu Dec 06 04:16:01 2018 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1gUk8u-0008SN-6Y for gllmg-musl@m.gmane.org; Thu, 06 Dec 2018 04:16:00 +0100 Original-Received: (qmail 18246 invoked by uid 550); 6 Dec 2018 03:18:09 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 18225 invoked from network); 6 Dec 2018 03:18:08 -0000 Content-Disposition: inline In-Reply-To: <20181206024340.202e0fc4@orivej.orivej.org> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:13506 Archived-At: On Thu, Dec 06, 2018 at 02:43:40AM +0000, Orivej Desh wrote: > * Rich Felker [2018-12-05] > > On Wed, Dec 05, 2018 at 10:27:16PM +0100, Ondřej Jirman wrote: > > > On Wed, Dec 05, 2018 at 08:47:59PM +0100, Markus Wichmann wrote: > > > > > > It's specified by POSIX: > > > > > > https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_wait.html > > > > > > Sates: "The sem_wait() function is interruptible by the delivery of a signal." > > > > This seems contradictory with EINTR being a "may fail" error, and, if > > interpreted the way you want to interpret it, seems to be > > contradictory with SA_RESTART semantics, since it doesn't say anything > > about whether that signal is an interrupting one. I think we should > > attempt to obtain a clarification on what the intent is here. Does "is > > interruptible" mean that it needs to fail on signals (only without > > SA_RESTART?) or simply that signal handlers must be permitted to run > > (i.e. the wait can't happen with signals blocked)? > > There is a definition of interruptible functions on the sigaction page: > > SA_RESTART > > This flag affects the behavior of interruptible functions; that is, those > specified to fail with errno set to [EINTR]. > > If set, and a function specified as interruptible is interrupted by this > signal, the function shall restart and shall not fail with [EINTR] unless > otherwise specified. > > If the flag is not set, interruptible functions interrupted by this signal > shall fail with errno set to [EINTR]. > > https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html OK, this seems correct. I still don't understand why EINTR is a "may fail" error; it's been that way at least back to SUSv2: http://pubs.opengroup.org/onlinepubs/7908799/xsh/sem_wait.html I'd like it if we could avoid the pre-linux-2.6.22 bug of spurious EINTR from SYS_futex, but I don't see any way to do so except possibly wrapping all signal handlers and implementing restart-vs-EINTR ourselves. So if we need to change this, it might just be a case where we say "well, sorry, your kernel is broken" if someone is using a broken kernel. Thoughts? Rich