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SubjectRe: [PATCH 01/15] Char: lp, protect LPGETSTATUS with port_mutex
On 05/07/2013 04:48 PM, Arnd Bergmann wrote:
> On Tuesday 07 May 2013, Jiri Slaby wrote:
>> From: "salina@us.ibm.com" <salina@us.ibm.com>
>>
>> The patch fixes a problem in the lp driver that can cause oopses as
>> follows:
>> process A: calls lp_write, which in turn calls
>> parport_ieee1284_write_compat, and that invokes
>> parport_wait_peripheral
>> process B: meanwhile does an ioctl(LPGETSTATUS), which call
>> lp_release_parport when done. This function will set
>> physport->cad = NULL.
>> process A: parport_wait_peripheral tries to dereference
>> physport->cad and dies
>>
>> So, protect that code with the port_mutex in order to protect against
>> simultaneous calls to lp_read/lp_write.
>>
>> Similar protection is probably required for ioctl(LPRESET)...
>>
>> This patch was done by IBM a while back and we (at suse) have that
>> since at least 2004 in our repos. Let's make it upstream.
>
> Hmm, it seems the driver has changed a bit since 2004, at least when
> I added the lp_mutex to lp_open()/lp_ioctl(). It's probably worth
> taking a look at the bigger picture now, to combine lp_mutex with
> lp_table[minor].port_mutex. I don't see any reason why we can't always
> use the per-device mutex.

Yeah, it looks sensible to me too to get rid of the lp_mutex, another
BKL left-over. However I don't have the hardware, the patch I attached
was taken from our tree and tested, at least some time ago. Patches to
clean that mess up welcome.

thanks,
--
js
suse labs


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