Date: Tue, 3 Jun 2014 16:21:00 -0700
From: Greg KH <gregkh@linuxfoundation.org>
To: Francesco Ruggeri <fruggeri@aristanetworks.com>
Cc: linux-kernel@vger.kernel.org, hare@suse.de, linux@roeck-us.net,
        fruggeri@arista.com
Subject: Re: pci: kernel crash in bus_find_device
Message-ID: <20140603232100.GA15247@kroah.com>
References: <20140603225502.F1C5122C07D5@bs320.sjc.aristanetworks.com>
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On Tue, Jun 03, 2014 at 03:55:02PM -0700, Francesco Ruggeri wrote:
> In-Reply-To: <20140523023141.GC13900@kroah.com>
> 
> 
> Hi Guenter,
> I got back to looking into this crash.
> Just as an example, the attached diffs also fix my bus_find_device problem for
> traversals that start from the head of the list and traverse it completely.
> They are very specific to the case of bus_find_device, and a complete solution
> would affect a lot of code.
> The main issue seems to be that when a device is found in a klist by say
> bus_find_device the klist_node reference should be returned to the caller,
> who should then decide whether to use it for the next klist search, drop it or
> maybe exchange it for a struct device reference. When resuming a search one
> should already hold a klist_node reference from the previous search.
> This model is broken by several functions using struct devices such as
> bus_find_device, which resume klist searches on the implicit assumption that
> holding a reference to the struct device is enough to acquire one on the
> klist_node. 
> The only reason that this has not been a big issue so far is probably that
> on most systems struct devices are not destroyed and created very often.

Not true, this happens on every USB device insertion and removal, and on
startup and shutdown.  What makes PCI special that we aren't hitting
these issues in USB and other subsystems that do a lot of device
creation/removal?

thanks,

greg k-h
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