From: Johan Hovold <jhovold@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>, 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: Fri, 25 Apr 2014 17:13:27 +0200 [thread overview]
Message-ID: <20140425151327.GF2206@localhost> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1404250953090.1140-100000@iolanthe.rowland.org>
On Fri, Apr 25, 2014 at 09:54:33AM -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".
Well, to be fair, if the try_module_get() *succeeds* it will prevent the
module from being unloaded (and otherwise the sysfs operation bails
out).
Johan
next prev parent reply other threads:[~2014-04-25 15:13 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 [this message]
2014-04-28 1:55 ` Li Zhong
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