From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Christie <michaelc@cs.wisc.edu>
Subject: Re: An oops will occur while SCSI core is being used in 3.4-rc1
Date: Tue, 10 Apr 2012 11:37:55 -0500
Message-ID: <4F8461E3.3050808@cs.wisc.edu>
References: <CAAxnys5O7PfWYv0q+BvhK2CP7X-_pNRa4j-Z1gSWHqLm8D8XmA@mail.gmail.com> <4F83EC71.90904@acm.org>
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To: Bart Van Assche <bvanassche@acm.org>
Cc: Elric Fu <elricfu1@gmail.com>, "Martin K. Petersen" <martin.petersen@oracle.com>, James Bottomley <JBottomley@Parallels.com>, linux-scsi@vger.kernel.org, Sarah Sharp <sarah.a.sharp@linux.intel.com>, Felipe Balbi <balbi@ti.com>, Alex He <alex.he@amd.com>, Andiry Xu <andiry.xu@amd.com>, Greg KH <gregkh@linuxfoundation.org>, Linux USB Mailing List <linux-usb@vger.kernel.org>, Alan Stern <stern@rowland.harvard.edu>

On 04/10/2012 03:16 AM, Bart Van Assche wrote:
> On 04/10/12 01:22, Elric Fu wrote:
> 
>> After debugging the code, I found the issue happened while the driver ran to
>> line 782 in scsi_send_eh_cmnd().
>>
>>  778 static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
>>  779                              int cmnd_size, int timeout, unsigned
>> sense_bytes)
>>  780 {
>>  781         struct scsi_device *sdev = scmd->device;
>>  782         struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
>>  783         struct Scsi_Host *shost = sdev->host;
>>  784         DECLARE_COMPLETION_ONSTACK(done);
>>  785         unsigned long timeleft;
>>  786         struct scsi_eh_save ses;
>>  787         int rtn;
>>
>> I know the code is submitted by you. I don't familiar with the scsi core.
>> It seems like the conversion process from scsi command to scsi driver
>> encounter a NULL pointer. Any idea?
> 
> 
> I have observed crashes at the same point while testing device removal
> with the ib_srp driver. As far as I can see that code was added through
> commit 18a4d0a22ed6c54b67af7718c305cd010f09ddf8 (February 9, 2012). The
> approach of that patch looks questionable to me: what guarantees that
> the struct scsi_driver will be available at the time the SCSI error
> handler needs it ?

If a scsi scan IO timesout then the driver will not be set yet. It is ok
to use scsi_cmd_to_driver in scsi_finish_cmd because of the req block pc
check (scsi scan IO set that flag and so do not hit that path).