scsi: libiscsi: Set expecting_cc_ua flag when stop_conn

Initiator need to recover session and reconnect to target, after calling stop_conn. And target will rebuild new session info, and mark ASC_POWERON_RESET ua sense for scsi devices belong to the target(device reset). After recovery, first scsi command(scmd) request to target will get ASC_POWERON_RESET(ua sense) + SAM_STAT_CHECK_CONDITION(status) in response.
According to scsi code: "scsi_done --> scsi_complete --> scsi_decide_disposition --> scsi_check_sense", if expecting_cc_ua = 0, scmd response with ASC_POWERON_RESET(ua sense) will ignore "cmd->retries <= cmd->allowed", fail directly. It will cause SCSI return io_error to upper layer without retry.
If we set expecting_cc_ua=1 in fail_scsi_tasks, SISC will retry the scmd which is response with ASC_POWERON_RESET. The scmd second request to target can successful, because target will clear ASC_POWERON_RESET in device pending ua_sense_list after first scmd request.

Signed-off-by: Xiang Zhang <hawkxiang.cpp@gmail.com>
---
 drivers/scsi/libiscsi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Hi Xiang,

kernel test robot noticed the following build warnings:

[auto build test WARNING on mkp-scsi/for-next]
[also build test WARNING on jejb-scsi/for-next linus/master v6.12-rc2 next-20241011]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Xiang-Zhang/scsi-libiscsi-Set-expecting_cc_ua-flag-when-stop_conn/20241011-161915
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git for-next
patch link:    https://lore.kernel.org/r/20241011081807.65027-1-hawkxiang.cpp%40gmail.com
patch subject: [PATCH] scsi: libiscsi: Set expecting_cc_ua flag when stop_conn
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20241012/202410122213.bq19EI34-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241012/202410122213.bq19EI34-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410122213.bq19EI34-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/scsi/libiscsi.c:634:3: warning: variable 'sc' is uninitialized when used here [-Wuninitialized]
     634 |                 sc->device->expecting_cc_ua = 1;
         |                 ^~
   drivers/scsi/libiscsi.c:618:22: note: initialize the variable 'sc' to silence this warning
     618 |         struct scsi_cmnd *sc;
         |                             ^
         |                              = NULL
   1 warning generated.


vim +/sc +634 drivers/scsi/libiscsi.c

   610	
   611	/*
   612	 * session back and frwd lock must be held and if not called for a task that
   613	 * is still pending or from the xmit thread, then xmit thread must be suspended
   614	 */
   615	static void __fail_scsi_task(struct iscsi_task *task, int err)
   616	{
   617		struct iscsi_conn *conn = task->conn;
   618		struct scsi_cmnd *sc;
   619		int state;
   620	
   621		if (cleanup_queued_task(task))
   622			return;
   623	
   624		if (task->state == ISCSI_TASK_PENDING) {
   625			/*
   626			 * cmd never made it to the xmit thread, so we should not count
   627			 * the cmd in the sequencing
   628			 */
   629			conn->session->queued_cmdsn--;
   630			/* it was never sent so just complete like normal */
   631			state = ISCSI_TASK_COMPLETED;
   632		} else if (err == DID_TRANSPORT_DISRUPTED) {
   633			state = ISCSI_TASK_ABRT_SESS_RECOV;
 > 634			sc->device->expecting_cc_ua = 1;
   635		} else
   636			state = ISCSI_TASK_ABRT_TMF;
   637	
   638		sc = task->sc;
   639		sc->result = err << 16;
   640		scsi_set_resid(sc, scsi_bufflen(sc));
   641		iscsi_complete_task(task, state);
   642	}
   643

On 10/12/24 2:55 AM, 张翔 wrote:
> 
> 
>     For commands coming from sd, then scsi_io_completion will end up calling
>     scsi_io_completion_action and seeing the UNIT_ATTENTION and will retry.
>     I'm not saying we shouldn't do a fix like you did below. Just want to
>     make sure I understand the case you describe above.
> 
>  
> For commands coming from sd, then scsi_complete calling scsi_decide_disposition to get "enum scsi_disposition", scsi_decide_disposition seeing the SAM_STAT_CHECK_CONDITION and calling scsi_check_sense function, then scsi_check_sense seeing UNIT_ATTENTION. If expecting_cc_ua == 1, scsi_check_sense return NEEDS_RETRY and scsi_complete will retry.


For sd, scsi_decide_disposition will return SUCCESS. scsi_complete will call
scsi_finish_command. In there we call the upper layer done callback, sd_done,
and it will return 0 as there are no good bytes. scsi_io_completion will
initially complete 0 bytes. If there are retries left then we call
scsi_io_completion_action which sees the UA and will retry.