On 10/13/2016 06:24 PM, Johannes Thumshirn wrote:

On Thu, Oct 13, 2016 at 05:15:25PM +0200, Steffen Maier wrote:

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I'm puzzled.

$ git bisect start fc_bsg master

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3087864ce3d7282f59021245d8a5f83ef1caef18 is the first bad commit
commit 3087864ce3d7282f59021245d8a5f83ef1caef18
Author: Johannes Thumshirn [off-list ref]
Date:   Wed Oct 12 15:06:28 2016 +0200

    scsi: don't use fc_bsg_job::request and fc_bsg_job::reply directl=

y

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    Don't use fc_bsg_job::request and fc_bsg_job::reply directly, but=

 use

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    helper variables bsg_request and bsg_reply. This will be helpfull=

  when

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    transitioning to bsg-lib.

    Signed-off-by: Johannes Thumshirn [off-list ref]

:040000 040000 140c4b6829d5cfaec4079716e0795f63f8bc3bd2 0d9fe22561567=

9550be91fbd9f84c09ab1e280fc M	drivers

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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 prev=

ious

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mail (dying in zfcp code).

[...]

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@@ -3937,6 +3944,7 @@ fc_bsg_request_handler(struct request_queue *q,=

 struct Scsi_Host *shost,

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 	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,

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 		/* 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 =3D 0;
-			job->reply->result =3D -ENOMSG;
+			bsg_reply =3D job->reply;
+			bsg_reply->reply_payload_rcv_len =3D 0;
+			bsg_reply->result =3D -ENOMSG;

Compiler optimization re-ordered above two lines and the first pointer=20
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=20
kernel page fault.

Does your suggested change for [PATCH v3 02/16], shuffling the=20
job->request_len checks, address above kernel page fault?

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 			job->reply_len =3D sizeof(uint32_t);
 			fc_bsg_jobdone(job);
 			spin_lock_irq(q->queue_lock);

Ahm and what exactly can break here? It's just assigning variables. Now=

I'm puzzled too.

--=20
Mit freundlichen Gr=FC=DFen / Kind regards
Steffen Maier

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