This is a note to let you know that I've just added the patch titled

scsi: libiscsi: Allow sd_shutdown on bad transport

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: scsi-libiscsi-allow-sd_shutdown-on-bad-transport.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Mon Apr 9 10:16:32 CEST 2018

From: Rafael David Tinoco rafael.tinoco@canonical.com Date: Thu, 7 Dec 2017 19:59:13 -0200 Subject: scsi: libiscsi: Allow sd_shutdown on bad transport

From: Rafael David Tinoco rafael.tinoco@canonical.com

[ Upstream commit d754941225a7dbc61f6dd2173fa9498049f9a7ee ]

If, for any reason, userland shuts down iscsi transport interfaces before proper logouts - like when logging in to LUNs manually, without logging out on server shutdown, or when automated scripts can't umount/logout from logged LUNs - kernel will hang forever on its sd_sync_cache() logic, after issuing the SYNCHRONIZE_CACHE cmd to all still existent paths.

PID: 1 TASK: ffff8801a69b8000 CPU: 1 COMMAND: "systemd-shutdow" #0 [ffff8801a69c3a30] __schedule at ffffffff8183e9ee #1 [ffff8801a69c3a80] schedule at ffffffff8183f0d5 #2 [ffff8801a69c3a98] schedule_timeout at ffffffff81842199 #3 [ffff8801a69c3b40] io_schedule_timeout at ffffffff8183e604 #4 [ffff8801a69c3b70] wait_for_completion_io_timeout at ffffffff8183fc6c #5 [ffff8801a69c3bd0] blk_execute_rq at ffffffff813cfe10 #6 [ffff8801a69c3c88] scsi_execute at ffffffff815c3fc7 #7 [ffff8801a69c3cc8] scsi_execute_req_flags at ffffffff815c60fe #8 [ffff8801a69c3d30] sd_sync_cache at ffffffff815d37d7 #9 [ffff8801a69c3da8] sd_shutdown at ffffffff815d3c3c

This happens because iscsi_eh_cmd_timed_out(), the transport layer timeout helper, would tell the queue timeout function (scsi_times_out) to reset the request timer over and over, until the session state is back to logged in state. Unfortunately, during server shutdown, this might never happen again.

Other option would be "not to handle" the issue in the transport layer. That would trigger the error handler logic, which would also need the session state to be logged in again.

Best option, for such case, is to tell upper layers that the command was handled during the transport layer error handler helper, marking it as DID_NO_CONNECT, which will allow completion and inform about the problem.

After the session was marked as ISCSI_STATE_FAILED, due to the first timeout during the server shutdown phase, all subsequent cmds will fail to be queued, allowing upper logic to fail faster.

Signed-off-by: Rafael David Tinoco rafael.tinoco@canonical.com Reviewed-by: Lee Duncan lduncan@suse.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/scsi/libiscsi.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)

--- a/drivers/scsi/libiscsi.c +++ b/drivers/scsi/libiscsi.c @@ -1696,6 +1696,15 @@ int iscsi_queuecommand(struct Scsi_Host */ switch (session->state) { case ISCSI_STATE_FAILED: + /* + * cmds should fail during shutdown, if the session + * state is bad, allowing completion to happen + */ + if (unlikely(system_state != SYSTEM_RUNNING)) { + reason = FAILURE_SESSION_FAILED; + sc->result = DID_NO_CONNECT << 16; + break; + } case ISCSI_STATE_IN_RECOVERY: reason = FAILURE_SESSION_IN_RECOVERY; sc->result = DID_IMM_RETRY << 16; @@ -1979,6 +1988,19 @@ enum blk_eh_timer_return iscsi_eh_cmd_ti

if (session->state != ISCSI_STATE_LOGGED_IN) { /* + * During shutdown, if session is prematurely disconnected, + * recovery won't happen and there will be hung cmds. Not + * handling cmds would trigger EH, also bad in this case. + * Instead, handle cmd, allow completion to happen and let + * upper layer to deal with the result. + */ + if (unlikely(system_state != SYSTEM_RUNNING)) { + sc->result = DID_NO_CONNECT << 16; + ISCSI_DBG_EH(session, "sc on shutdown, handled\n"); + rc = BLK_EH_HANDLED; + goto done; + } + /* * We are probably in the middle of iscsi recovery so let * that complete and handle the error. */ @@ -2082,7 +2104,7 @@ done: task->last_timeout = jiffies; spin_unlock(&session->frwd_lock); ISCSI_DBG_EH(session, "return %s\n", rc == BLK_EH_RESET_TIMER ? - "timer reset" : "nh"); + "timer reset" : "shutdown or nh"); return rc; } EXPORT_SYMBOL_GPL(iscsi_eh_cmd_timed_out);

Patches currently in stable-queue which might be from rafael.tinoco@canonical.com are

queue-4.15/scsi-libiscsi-allow-sd_shutdown-on-bad-transport.patch