> -----Original Message----- > From: Bart Van Assche [mailto:bart.vanass...@sandisk.com] > Sent: Monday, May 15, 2017 5:01 PM > To: j...@linux.vnet.ibm.com; linux-scsi@vger.kernel.org; linux- > ker...@vger.kernel.org; Long Li <lon...@microsoft.com>; > martin.peter...@oracle.com > Cc: Stephen Hemminger <sthem...@microsoft.com>; KY Srinivasan > <k...@microsoft.com> > Subject: Re: [PATCH] scsi: zero per-cmd driver data for each MQ I/O > > On Mon, 2017-05-15 at 23:32 +0000, Long Li wrote: > > Thanks for looking! Yes this is for chasing a bug. > > > > With the patch, we also zero the private data used by lower layer > > driver, in addition to the private data in scsi_cmnd. > > Hello Long, > > What bug did you encounter, with which combination of ULP (sd?) and LLD SCSI > driver(s) and for which request type (REQ_OP_*)? You will have to mention > that information in the patch description anyway if you want your patch to get > accepted. > > If the bug that you encountered only occurs with a single LLD, would it be > possible to implement a fix by modifying the LLD instead of the SCSI core?
The bug I encounter is that in hv_storvsc (a LLD), sometime we are getting stale data in the private driver data memory allocated by SCSI. As a LLD, we expect the memory allocated by SCSI to be zeroed. If not we may send unexpected commands to the device. A little background on private data: In LLD's scsi_host_template, the driver may optionally ask SCSI to allocate its private driver memory for each command, by specifying cmd_size. This memory is allocated at the end of scsi_cmnd by SCSI. Later when SCSI queues a command, the LLD can use scsi_cmd_priv to get its private data. hv_storvsc doesn't clear its private data before use. I'm not sure about other LLD drivers. Although it's possible to fix it in LLD not SCSI core, I think that is not the ideal place to do it. Whoever is allocating the SCSI command should also zero it. There is a similar patch that fixed a similar issue for non-MQ case: commit ee5242360424b9b967454e9183767323d10cf985 I'm sorry I should have put more details in the patch. > > Thanks, > > Bart.
