On 10/28/2016 11:53 AM, Steffen Maier wrote:
>
>
> On 10/13/2016 06:24 PM, Johannes Thumshirn wrote:
>> On Thu, Oct 13, 2016 at 05:15:25PM +0200, Steffen Maier wrote:
>>> I'm puzzled.
>>>
>>> $ git bisect start fc_bsg master
>
>>>> 3087864ce3d7282f59021245d8a5f83ef1caef18 is the first bad commit
>>>> commit 3087864ce3d7282f59021245d8a5f83ef1caef18
>>>> Author: Johannes Thumshirn <jthumshirn@xxxxxxx>
>>>> Date: Wed Oct 12 15:06:28 2016 +0200
>>>>
>>>> scsi: don't use fc_bsg_job::request and fc_bsg_job::reply directly
>>>>
>>>> Don't use fc_bsg_job::request and fc_bsg_job::reply directly,
>>>> but use
>>>> helper variables bsg_request and bsg_reply. This will be
>>>> helpfull when
>>>> transitioning to bsg-lib.
>>>>
>>>> Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
>>>>
>>>> :040000 040000 140c4b6829d5cfaec4079716e0795f63f8bc3bd2
>>>> 0d9fe225615679550be91fbd9f84c09ab1e280fc M drivers
>>>
>>> From there (on the reverse bisect path) I get the following Oops,
>>> except for the full patch set having another stack trace as in my
>>> previous
>>> mail (dying in zfcp code).
>>>
>>
>> [...]
>>
>>>
>>>> @@ -3937,6 +3944,7 @@ fc_bsg_request_handler(struct request_queue
>>>> *q, struct Scsi_Host *shost,
>>>> struct request *req;
>>>> struct fc_bsg_job *job;
>>>> enum fc_dispatch_result ret;
>>>> + struct fc_bsg_reply *bsg_reply;
>>>>
>>>> if (!get_device(dev))
>>>> return;
>>>> @@ -3973,8 +3981,9 @@ fc_bsg_request_handler(struct request_queue
>>>> *q, struct Scsi_Host *shost,
>>>> /* check if we have the msgcode value at least */
>>>> if (job->request_len < sizeof(uint32_t)) {
>>>> BUG_ON(job->reply_len < sizeof(uint32_t));
>>>> - job->reply->reply_payload_rcv_len = 0;
>>>> - job->reply->result = -ENOMSG;
>>>> + bsg_reply = job->reply;
>>>> + bsg_reply->reply_payload_rcv_len = 0;
>>>> + bsg_reply->result = -ENOMSG;
>
> Compiler optimization re-ordered above two lines and the first pointer
> derefence is bsg_reply->result [field offset 0] where bsg_reply is NULL.
> The assignment tries to write to memory at address NULL causing the
> kernel page fault.
>
I spoke to our compiler people, and they strongly believed this not to
be the case. Or, put it the other way round, if such a thing would
happen it would be a compiler issue.
Have you checked the compiler output?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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