Re: [PATCH v2 1/5] vfio: ccw: fix cleanup if cp_prefetch fails

Halil Pasic
2018-04-23T12:00:11Z

On 04/23/2018 01:40 PM, Cornelia Huck wrote:
> On Mon, 23 Apr 2018 13:01:09 +0200
> Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:
>
>> From: Halil Pasic <pasic@linux.vnet.ibm.com>
>>
>> If the translation of a channel program fails, we may end up attempting
>> to clean up (free, unpin) stuff that never got translated (and allocated,
>> pinned) in the first place.
>>
>> By adjusting the lengths of the chains accordingly (so the element that
>> failed, and all subsequent elements are excluded) cleanup activities
>> based on false assumptions can be avoided.
>>
>> Let's make sure cp_free works properly after cp_prefetch returns with an
>> error by setting ch_len of a ccw chain to the number of the translated
>> CCWs on that chain.
>
> Should that be cc:stable? This problem has been there probably since we
> introduced vfio-ccw, no?
>

Seems emails crossed in flight. Yes I think it should
be cc stable and this was broken since the very beginning.

>>
>> Acked-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
>> Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
>> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>> Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
>> ---
>> drivers/s390/cio/vfio_ccw_cp.c | 13 ++++++++++++-
>> 1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
>> index 2c7550797ec2..62d66e195304 100644
>> --- a/drivers/s390/cio/vfio_ccw_cp.c
>> +++ b/drivers/s390/cio/vfio_ccw_cp.c
>> @@ -715,6 +715,10 @@ void cp_free(struct channel_program *cp)
>> * and stores the result to ccwchain list. @cp must have been
>> * initialized by a previous call with cp_init(). Otherwise, undefined
>> * behavior occurs.
>> + * For each chain composing the channel program:
>> + * - On entry ch_len holds the count of CCW to be translated.
>> + * - On exit ch_len is adjusted to the count of successfully translated CCW.
>> + * This allows cp_free to find in ch_len the count of CCW to free in a chain.
>
> s/CCW/CCWs/ (x3)?
>

Nod.

> Can change on applying.
>
>> *
>> * The S/390 CCW Translation APIS (prefixed by 'cp_') are introduced
>> * as helpers to do ccw chain translation inside the kernel. Basically
>> @@ -749,11 +753,18 @@ int cp_prefetch(struct channel_program *cp)
>> for (idx = 0; idx < len; idx++) {
>> ret = ccwchain_fetch_one(chain, idx, cp);
>> if (ret)
>> - return ret;
>> + goto out_err;
>> }
>> }
>>
>> return 0;
>> +out_err:
>> + /* Only cleanup the chain elements that were actually translated. */
>> + chain->ch_len = idx;
>> + list_for_each_entry_continue(chain, &cp->ccwchain_list, next) {
>> + chain->ch_len = 0;
>> + }
>> + return ret;
>> }
>>
>> /**
>
> Else, looks good.
>