linux-kernel - Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device online store callbacks

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, 17 Apr 2014 11:06:40 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, gregkh@...uxfoundation.org,
	rafael.j.wysocki@...el.com, toshi.kani@...com
Subject: Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device
 online store callbacks

Hello,

On Thu, Apr 17, 2014 at 11:05:53AM +0800, Li Zhong wrote:
> It seems to me cpu_add_remove_lock is always taken after
> device_hotplug_lock.
> 
> So if cpu_add_remove_lock has been acquired by device removing process,
> then it means the other online/offline process couldn't successfully try
> lock device_hotplug_lock, and will release s_active with a restart
> syscall error;
> 
> if cpu_add_remove_lock has been acquired by online/offline process, then
> it should already hold device_hotlug_lock, and keeps the device removing
> process waiting at device_hotplug_lock. So online/offline process could
> release the lock, and finally release s_active soon. 

I see.  That's kinda nasty tho and lockdep of course doesn't know
about it and generates spurious warnings.

> But after some further thinking, I seem to understand your point.
> s_active has lock order problem with the other series of hotplug related
> locks, so it's better to take s_active out of the dependency chain,
> rather than the first of the other series of locks? like you suggested
> below.

Yeah, I think that'd be the right thing to do and we can revert the
previous convolution.

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/