From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41345) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Za5vR-0001aG-Vd for qemu-devel@nongnu.org; Thu, 10 Sep 2015 13:46:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Za5vM-0007Cr-Sj for qemu-devel@nongnu.org; Thu, 10 Sep 2015 13:46:21 -0400 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:47594) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Za5vM-0007Cg-MO for qemu-devel@nongnu.org; Thu, 10 Sep 2015 13:46:16 -0400 Received: from compute6.internal (compute6.nyi.internal [10.202.2.46]) by mailout.nyi.internal (Postfix) with ESMTP id 1A511209FA for ; Thu, 10 Sep 2015 13:46:15 -0400 (EDT) Date: Thu, 10 Sep 2015 13:46:53 -0400 From: "Emilio G. Cota" Message-ID: <20150910174653.GA17236@flamenco> References: <1440375847-17603-1-git-send-email-cota@braap.org> <1440375847-17603-12-git-send-email-cota@braap.org> <87zj0u8l3q.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87zj0u8l3q.fsf@linaro.org> Subject: Re: [Qemu-devel] [RFC 11/38] qemu-thread: handle spurious futex_wait wakeups List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex =?iso-8859-1?Q?Benn=E9e?= Cc: mttcg@listserver.greensocs.com, mark.burton@greensocs.com, a.rigo@virtualopensystems.com, qemu-devel@nongnu.org, guillaume.delbergue@greensocs.com, pbonzini@redhat.com, Frederic Konrad On Thu, Sep 10, 2015 at 14:22:49 +0100, Alex Bennée wrote: > Emilio G. Cota writes: > > > Signed-off-by: Emilio G. Cota > > --- > > util/qemu-thread-posix.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c > > index 04dae0f..3760e27 100644 > > --- a/util/qemu-thread-posix.c > > +++ b/util/qemu-thread-posix.c > > @@ -303,7 +303,16 @@ static inline void futex_wake(QemuEvent *ev, int n) > > > > static inline void futex_wait(QemuEvent *ev, unsigned val) > > { > > - futex(ev, FUTEX_WAIT, (int) val, NULL, NULL, 0); > > + while (futex(ev, FUTEX_WAIT, (int) val, NULL, NULL, 0)) { > > + switch (errno) { > > + case EWOULDBLOCK: > > + return; > > + case EINTR: > > + break; /* get out of switch and retry */ > > + default: > > + abort(); > > I'd be tempted to error_exit with the errno in this case so additional > information is reported before we bail out. Yes that's a good suggestion. > The man pages seems to indicate other errnos are possible for FUTUX_WAIT > although they may be unlikely: > > EACCES No read access to futex memory. > EFAULT Error retrieving timeout information from user space. > > I guess things would have gone very wrong for these > > EINVAL Invalid argument. > > Hard to get wrong > > ENFILE The system limit on the total number of open files has > been reached. > > Might happen under system load? > > ENOSYS Invalid operation specified in op. > > Hardcoded op so no > > ETIMEDOUT > Timeout during the FUTEX_WAIT operation. > > No timeout specified so we shouldn't hit it Of these I'd say all would be bugs in our code except for ENFILE, so it might be worth adding. Thanks, Emilio