lists.openwall.net   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  linux-hardening  linux-cve-announce  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:	Wed, 20 Sep 2006 10:06:46 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	Mike Waychison <mikew@...gle.com>, linux-mm@...ck.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [RFC] page fault retry with NOPAGE_RETRY

On Tue, 2006-09-19 at 16:59 -0700, Andrew Morton wrote:
> On Wed, 20 Sep 2006 09:50:35 +1000
> Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > On Tue, 2006-09-19 at 16:35 -0700, Mike Waychison wrote:
> > > Patch attached.
> > > 
> > > As Andrew points out, the logic is a bit hacky and using a flag in 
> > > current->flags to determine whether we have done the retry or not already.
> > > 
> > > I too think the right approach to being able to handle these kinds of 
> > > retries in a more general fashion is to introduce a struct 
> > > pagefault_args along the page faulting path.  Within it, we could 
> > > introduce a reason for the retry so the higher levels would be able to 
> > > better understand what to do.
> > 
> >  .../...
> > 
> > I need to re-read your mail and Andrew as at this point, I don't quite
> > see why we need that args and/or that current->flags bit instead of
> > always returning all the way to userland and let the faulting
> > instruction happen again (which means you don't block in the kernel, can
> > take signals etc...
> 
> That would amount to a busy wait, waiting for the disk IO to complete.
> 
> So we need to go to sleep somewhere (in D state, because we _are_ waiting
> for disk IO).  Returning all the way to userspace and immediately retaking
> the fault is unneeded extra work.

No, I'm not saying immediately... you do the wait thing in filemap.c.
Anyway, see my other message.

> > thus do you actually need to prevent multiple
> > retries ?)
> 
> I expect there are livelock scenarios.  For example, process A could spin
> on posix_fadvise(some libc text page, POSIX_FADV_DONTNEED), perhaps causing
> other applications to get permanently stuck in the kernel.

Unless you add a way to handle signals.. see my other mail.

Ben.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists