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:	Thu, 30 Aug 2012 18:43:59 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tj@...nel.org, bharrosh@...asas.com,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by
 stacking drivers

On Thu, Aug 30, 2012 at 06:07:45PM -0400, Vivek Goyal wrote:
> On Wed, Aug 29, 2012 at 10:13:45AM -0700, Kent Overstreet wrote:
> 
> [..]
> > > Performance aside, punting submission to per device worker in case of deep
> > > stack usage sounds cleaner solution to me.
> > 
> > Agreed, but performance tends to matter in the real world. And either
> > way the tricky bits are going to be confined to a few functions, so I
> > don't think it matters that much.
> > 
> > If someone wants to code up the workqueue version and test it, they're
> > more than welcome...
> 
> Here is one quick and dirty proof of concept patch. It checks for stack
> depth and if remaining space is less than 20% of stack size, then it
> defers the bio submission to per queue worker.

I can't think of any correctness issues. I see some stuff that could be
simplified (blk_drain_deferred_bios() is redundant, just make it a
wrapper around blk_deffered_bio_work()).

Still skeptical about the performance impact, though - frankly, on some
of the hardware I've been running bcache on this would be a visible
performance regression - probably double digit percentages but I'd have
to benchmark it.  That kind of of hardware/usage is not normal today,
but I've put a lot of work into performance and I don't want to make
things worse without good reason.

Have you tested/benchmarked it?

There's scheduling behaviour, too. We really want the workqueue thread's
cpu time to be charged to the process that submitted the bio. (We could
use a mechanism like that in other places, too... not like this is a new
issue).

This is going to be a real issue for users that need strong isolation -
for any driver that uses non negligable cpu (i.e. dm crypt), we're
breaking that (not that it wasn't broken already, but this makes it
worse).

I could be convinced, but right now I prefer my solution.
--
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