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  PHC 
Open Source and information security mailing list archives
 
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Sat, 21 Apr 2012 08:32:55 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	netdev@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>
Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work()

On Fri, Apr 20, 2012 at 4:32 PM, Yong Zhang <yong.zhang0@...il.com> wrote:
> On Fri, Apr 20, 2012 at 01:18:19AM -0700, Stephen Boyd wrote:
>> On 4/20/2012 12:18 AM, Yong Zhang wrote:
>> > On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote:
>> >> complain in the case where the work is not queued. That case is not a
>> >> false positive. We will get a lockdep warning if the work is running
>> > IIRC, flush_work() is just a nop when a work is not queued nor running.
>>
>> Agreed, but it's better to always print a lockdep warning instead of
>> only when the deadlock is going to occur.
>
> It will IMHO.

After reconsidering this issue, I recognize I'm wrong from the beginning.
My suggestion will only warn on the real deadlock. It doesn't follow
what lockdep want to achieve. Sorry for that.

BTW, your latest patch should work :)

Thanks,
Yong

>
>>
>> >
>> >> (when start_flush_work() returns true) solely with the
>> >> lock_map_acquire() on cwq->wq->lockdep_map.
>> > Yeah, that is the point we use lockdep to detect deadlock for workqueue.
>> >
>> > But when looking at start_flush_work(), for some case
>> > !(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER),
>> > lock_map_acquire_read() is called, but recursive read is not added to
>> > the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map)
>> > is called, deadlock will not be detected. I hope you don't hit that
>> > special case.
>>
>> Hmm. Originally I had what you suggested in my patch but I left it out
>> because I wasn't sure if it would cause false positives.
>> Do you see any
>> possibility for false positives?
>
> No, I don't. My test indeed show nothing (just build and boot).
>
>>I'll add it back in if not.
>
> It's great if you can try it :)
>
> Thanks,
> Yong



-- 
Only stand for myself
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists