From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bart Van Assche <bvanassche@acm.org>
Subject: Re: An oops will occur while SCSI core is being used in 3.4-rc1
Date: Tue, 10 Apr 2012 08:16:49 +0000
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To: Elric Fu <elricfu1@gmail.com>
Cc: "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 04/10/12 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 ? At least the sd driver explicitly resets that pointer
in its scsi_disk_release() function.

Thanks,

Bart.