illumos gate

OS: oi_151a

when issuing SCSI read commands to a iscsi target on Linux (SCST 2.1.0, scst_cdrom module), I regularly see the connection being dropped by OI:

Mar 25 17:58:10 linuxdev kernel: [0]: iscsi-scst: __iscsi_state_change:444:***ERROR***: Connection with initiator iqn.1986-03.com.sun:01:00900d4901ff.4f62ff12 unexpectedly closed!

After doing a network trace with Wireshark, I noticed that OI indeed closes the socket connection unexpectedly.
I then started investigating the idm module using dtrace, and found that a page fault occurs in kcopy_nta() and it then
returns 14 (EFAULT):

0  > idm_fill_iov                          ro 0 dlength 8192
  0  < idm_fill_iov                          8192
  0  > idm_iov_sorecv                        so ffffff014a6f5288 iop ffffff014c1c36e0 iovlen 1 total_len 8192
  0    -> ksocket_recvmsg                     ks ffffff014a6f5288 msg ffffff000498eab0 flags 64 cr ffffff0148468db0
  0      -> socket_recvmsg                    so ffffff014a6f5288 msg ffffff000498eab0 uiop ffffff000498ea10, cr ffffff0148468db0
  0        -> so_recvmsg                      so ffffff014a6f5288 msg ffffff000498eab0 uiop ffffff000498ea10, cr ffffff0148468db0
  0          -> so_dequeue_msg                so ffffff014a6f5288
  0            -> uiomove                     p ffffff01812d50e2 size 1400 uiop ffffff000498ea10 resid 8192, uio_segflg 1
  0              -> kcopy_nta                 from ffffff01812d50e2 to ffffff0170012000 size 1400, copy_cached 1
  0                -> pagefault               page fault on addr 0xffffff0170012000, fault type = 1
  0                < kcopy_nta               14 uiop ffffff000498ea10 from ffffff01812d50e2 to ffffff0170012000
  0              <- uiomove                   14 uiop ffffff000498ea10 (UIOMOVE ERROR!)
  0            <- socopyoutuio                0
  0          <- so_dequeue_msg                14
  0        <- so_recvmsg                      14
  0      <- socket_recvmsg                    14
  0    <- ksocket_recvmsg                     14
  0  <- idm_iov_sorecv                        14
  0  <- idm_sorecvdata                        4
  0  <- idm_sorecv_scsidata                   4
  0  -> idm_conn_event
  0    -> idm_conn_event_handler
  0      -> idm_so_conn_disconnect

The EFAULT error causes a connection failed status in idm, and the socket connection is closed.
The SCSI read command terminates with a transport error.
I can reproduce this very easily.

I would appreciate it if someone could give me some hints on how to investigate why this page fault
occurs.