linux-kernel - Re: USB device cannot be reconnected and khubd "blocked for more than 120 seconds"

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]

Message-ID: <Pine.LNX.4.44L0.1301152253070.26877-100000@netrider.rowland.org>
Date:	Tue, 15 Jan 2013 23:01:15 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <tj@...nel.org>
cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ming Lei <ming.lei@...onical.com>,
	Alex Riesen <raa.lkml@...il.com>, Jens Axboe <axboe@...nel.dk>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: USB device cannot be reconnected and khubd "blocked for more
 than 120 seconds"

On Tue, 15 Jan 2013, Tejun Heo wrote:

> Hello, Arjan.
> 
> On Tue, Jan 15, 2013 at 04:25:54PM -0800, Arjan van de Ven wrote:
> > async fundamentally had the concept of a monotonic increasing number,
> > and that you could always wait for "everyone before me".
> > then people (like me) wanted exceptions to what "everyone" means ;-(
> > I'm ok with going back to a single space and simplify the world.
> 
> If we want (or need) finer grained operation, we'll probably have to
> head the other direction, so that we can definitively tell that an
> async operation belongs to domains system, module load A and B, so
> that each waiter knows what to wait for.
> 
> The current domain implementation is somewhere inbetween.  It's not
> completely simplistic system and at the same time not developed enough
> to do properly stacked flushing.

I like your idea of chronological synchronization: Insist that anybody
who wants to flush async jobs must get a cookie, and then only allow
them to wait for async jobs started after the cookie was issued.

I don't know if this is possible with the current implementation.  It 
would require changing every call to async_synchronize_*(), and in a 
nontrivial way.  But it might provide a proper solution to all these 
problems.

Can you think of any reasons why it wouldn't work in principle?  It 
would prevent code from doing "wait until all currently-running async 
jobs have finished" -- but arguably, nobody should be allowed to do 
that anyway.

Alan Stern


--
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/