On Tue, 2017-05-16 at 17:31 +0000, Long Li wrote: > > -----Original Message----- > > From: Bart Van Assche [mailto:Bart.VanAssche@xxxxxxxxxxx] > > Sent: Monday, May 15, 2017 5:01 PM > > To: jejb@xxxxxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; linux- > > kernel@xxxxxxxxxxxxxxx; Long Li <longli@xxxxxxxxxxxxx>; > > martin.petersen@xxxxxxxxxx > > Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>; KY Srinivasan > > <kys@xxxxxxxxxxxxx> > > 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. Hello Long, Thank you for the feedback. I'm working on a patch series that merges the scsi-sq and scsi-mq code paths for command initialization and that should fix the bug you encountered. Bart.
