linux-kernel - Re: [PATCH] workqueue: Document exceptions to work item non-reentrancy guarantee

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: <20140218153056.GC30043@htj.dyndns.org>
Date:	Tue, 18 Feb 2014 10:30:56 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	stable@...r.kernel.org
Subject: Re: [PATCH] workqueue: Document exceptions to work item
 non-reentrancy guarantee

On Mon, Feb 17, 2014 at 09:29:34PM -0500, Peter Hurley wrote:
> >It never would have occurred to me that you could safely change the
> >function for a work item that is already scheduled or running.
> >Especially given that PREPARE_WORK() is just a simple assignment (i.e.
> >no serialisation).
> 
> process_one_work() has an established order that safely allows for
> resetting the work function and scheduling the work, and further
> guaranteeing that the new work function will run.
> 
> Further, existing memory barriers ensure that
> 1. The new work function is visible on all cpus before testing if
>    the work is already pending.
> 2. The new work function is stored as the worker's current function
>    before the work is marked as not pending.
> 
> If this wasn't possible, then single-threaded workqueues could
> not be used for multiple functions without flushing work.
> 
> I wonder if the floppy driver is broken too.

Ugh... I'd just rather remove PREPARE_WORK altogether.  It's a pretty
dumb thing to do anyway.  I'll look into it.

Thanks.

-- 
tejun
--
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/