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From: Li Zhong <zhong@linux.vnet.ibm.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Tejun Heo <tj@kernel.org>, Johan Hovold <jhovold@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	rafael.j.wysocki@intel.com
Subject: Re: [PATCH] USB: serial: fix sysfs-attribute removal deadlock
Date: Mon, 28 Apr 2014 09:55:00 +0800	[thread overview]
Message-ID: <1398650100.3046.64.camel@ThinkPad-T5421> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1404250953090.1140-100000@iolanthe.rowland.org>

On Fri, 2014-04-25 at 09:54 -0400, Alan Stern wrote:
> On Fri, 25 Apr 2014, Li Zhong wrote:
> 
> > > I don't get why try_module_get() matters here.  We can't call into
> > > ->store if the object at hand is already destroyed and the underlying
> > > module can't go away if the target device is still alive.
> > > try_module_get() doesn't actually protect the object.  Why does that
> > > matter?  This is self removal, right?  Can you please take a look at
> > > kernfs_remove_self()?
> > 
> > This is about one process writing something to driver attributes, and
> > one process trying to unload this driver. 
> > 
> > I think try_module_get() could detect whether the driver is being
> > unloaded, and if not, prevent it from being unloaded, so it could
> > protect the object here by not allow the driver to be unloaded.
> 
> That isn't how try_module_get() works.  If the module is being 
> unloaded, try_module_get() simply fails.  It does not prevent the 
> module from being unloaded -- that's why its name begins with "try".

Yes, I know that. What I said above is for the case when
try_module_get() detects the driver is NOT being unloaded, and increases
the reference counter. 

Thanks, Zhong
> 
> Alan Stern
> 



      parent reply	other threads:[~2014-04-28  1:55 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-23  9:32 [PATCH] USB: serial: fix sysfs-attribute removal deadlock Johan Hovold
2014-04-23 14:19 ` Tejun Heo
2014-04-24  8:29   ` Li Zhong
2014-04-24 14:35     ` Tejun Heo
2014-04-24 14:52       ` Johan Hovold
2014-04-25  2:16         ` Li Zhong
2014-04-25 10:15           ` Johan Hovold
2014-04-28  0:39             ` Li Zhong
2014-05-02 15:20               ` Tejun Heo
2014-04-25 13:59           ` Alan Stern
2014-04-28  1:58             ` Li Zhong
2014-04-25  2:15       ` Li Zhong
2014-04-25 13:54         ` Alan Stern
2014-04-25 15:13           ` Johan Hovold
2014-04-28  1:55           ` Li Zhong [this message]

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