lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 1 Jan 2013 11:58:14 -0500
From:	"Junchang(Jason) Wang" <>
To:	Eric Wong <>
	Hans Verkuil <>,
	Jiri Olsa <>, Jonathan Corbet <>,
	Al Viro <>,
	Davide Libenzi <>,
	Hans de Goede <>,
	Mauro Carvalho Chehab <>,
	David Miller <>,
	Eric Dumazet <>,
	Andrew Morton <>,
	Linus Torvalds <>,
	Andreas Voellmy <>,,
Subject: Re: [PATCH] poll: prevent missed events if _qproc is NULL

Hi Eric and list,

Thanks a lot. The patch solves our (Andreas and my) issue in using
epoll. Here's our test program  We
are using Linux 3.7.1 and a server with 80 cores.



On Mon, Dec 31, 2012 at 6:24 PM, Eric Wong <> wrote:
> Eric Wong <> wrote:
> > This patch seems to fix my issue with ppoll() being stuck on my
> > SMP machine:
> OK, it doesn't fix my issue, but it seems to make it harder-to-hit...
> > The change to sock_poll_wait() in
> > commit 626cf236608505d376e4799adb4f7eb00a8594af
> >   (poll: add poll_requested_events() and poll_does_not_wait() functions)
> > seems to have allowed additional cases where the SMP memory barrier
> > is not issued before checking for readiness.
> >
> > In my case, this affects the select()-family of functions
> > which register descriptors once and set _qproc to NULL before
> > checking events again (after poll_schedule_timeout() returns).
> > The set_mb() barrier in poll_schedule_timeout() appears to be
> > insufficient on my SMP x86-64 machine (as it's only an xchg()).
> >
> > This may also be related to the epoll issue described by
> > Andreas Voellmy in
> However, I believe my patch will still fix Andreas' issue with epoll
> due to how ep_modify() uses a NULL qproc when calling ->poll().
> (I've never been able to reproduce Andreas' issue on my 4-core system,
>  but he's been hitting it since 3.4 (at least))
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists