Re: kern/46896: iSCSI initiator ccb_pool gets corrupted

["Michael L. Hitch" <mhitch%lightning.msu.montana.edu@localhost>]

The following reply was made to PR kern/46896; it has been noted by GNATS.

From: "Michael L. Hitch" <mhitch%lightning.msu.montana.edu@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/46896: iSCSI initiator ccb_pool gets corrupted
Date: Sat, 8 Sep 2012 20:17:29 -0600 (MDT)

 >> How-To-Repeat:
 >      I suspect this problem is relatively rare, and needs something similar
 >      to my above described setup to get enough random activity with the iSCSI
 >      target to duplicate.
 
    I had added tagged queueing support for iscsi in my netbsd-6 while 
 debugging the problem, and wanted to test tagged queueing in -current 
 before commiting that change.  With tagged queueuing, things very quickly 
 went awry and hung when I tried to start the DOMU, so adding tagged 
 queueing should make this problem much more repeatable.
 
 >> Fix:
 >      If the problem is multiple processing of a ccb on the ccbs_waiting 
 > queue,
 >      try to prevent that from happening, or at least prevent it from 
 > clobbering
 >      the ccb_pool and ccbs_waiting queues.
 
    What I've discovered so far:  I do indeed see ccbs passed to wake_ccb() 
 which are not on the ccbs_waiting queue.  If I check the ccbs_waiting 
 queue and only remove the ccb if it's on that queue, I do not have the 
 problems of ccb corruption.  Also, I noticed that all the ccbs that passed 
 to wake_ccb() have a dispostion of CCBDISP_SCSIPI, which presumably are 
 the result of requests from the scsipi layer and will report their status 
 back to the scsipi layer.  I don't yet know if there are any ccbs with 
 CCBDISP_SCSIPI that get added to the ccbs_waiting queue, and my cursory 
 attempt to follow the logic of the scsipi requests got me rather lost.
 
    I think that the iscsi initiator working as well as it has for several 
 people is pure luck and happenstance.
 
 --
 Michael L. Hitch                       mhitch%montana.edu@localhost
 Computer Consultant
 Information Technology Center
 Montana State University       Bozeman, MT     USA