scsi: docs: convert scsi_eh.txt to ReST
Link: https://lore.kernel.org/r/300314197f2e6a3258200711e825aa04c9e8ceaf.1583136624.git.mchehab+huawei@kernel.org Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Mauro Carvalho Chehab
committed by
Martin K. Petersen
Martin K. Petersen
parent
731fc16c2f
commit
e513de9936
@@ -401,7 +401,7 @@ Error handling
|
||||
==============
|
||||
|
||||
This chapter describes how errors are handled under libata. Readers are
|
||||
advised to read SCSI EH (Documentation/scsi/scsi_eh.txt) and ATA
|
||||
advised to read SCSI EH (Documentation/scsi/scsi_eh.rst) and ATA
|
||||
exceptions doc first.
|
||||
|
||||
Origins of commands
|
||||
|
||||
@@ -32,5 +32,6 @@ Linux SCSI Subsystem
|
||||
ppa
|
||||
qlogicfas
|
||||
scsi-changer
|
||||
scsi_eh
|
||||
|
||||
scsi_transport_srp/figures
|
||||
|
||||
@@ -1,12 +1,14 @@
|
||||
.. SPDX-License-Identifier: GPL-2.0
|
||||
|
||||
=======
|
||||
SCSI EH
|
||||
======================================
|
||||
=======
|
||||
|
||||
This document describes SCSI midlayer error handling infrastructure.
|
||||
Please refer to Documentation/scsi/scsi_mid_low_api.txt for more
|
||||
information regarding SCSI midlayer.
|
||||
|
||||
TABLE OF CONTENTS
|
||||
.. TABLE OF CONTENTS
|
||||
|
||||
[1] How SCSI commands travel through the midlayer and to EH
|
||||
[1-1] struct scsi_cmnd
|
||||
@@ -25,9 +27,11 @@ TABLE OF CONTENTS
|
||||
[2-2-3] Things to consider
|
||||
|
||||
|
||||
[1] How SCSI commands travel through the midlayer and to EH
|
||||
1. How SCSI commands travel through the midlayer and to EH
|
||||
==========================================================
|
||||
|
||||
[1-1] struct scsi_cmnd
|
||||
1.1 struct scsi_cmnd
|
||||
--------------------
|
||||
|
||||
Each SCSI command is represented with struct scsi_cmnd (== scmd). A
|
||||
scmd has two list_head's to link itself into lists. The two are
|
||||
@@ -38,14 +42,16 @@ otherwise stated scmds are always linked using scmd->eh_entry in this
|
||||
discussion.
|
||||
|
||||
|
||||
[1-2] How do scmd's get completed?
|
||||
1.2 How do scmd's get completed?
|
||||
--------------------------------
|
||||
|
||||
Once LLDD gets hold of a scmd, either the LLDD will complete the
|
||||
command by calling scsi_done callback passed from midlayer when
|
||||
invoking hostt->queuecommand() or the block layer will time it out.
|
||||
|
||||
|
||||
[1-2-1] Completing a scmd w/ scsi_done
|
||||
1.2.1 Completing a scmd w/ scsi_done
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
For all non-EH commands, scsi_done() is the completion callback. It
|
||||
just calls blk_complete_request() to delete the block layer timer and
|
||||
@@ -57,6 +63,7 @@ looks at the scmd->result value and sense data to determine what to do
|
||||
with the command.
|
||||
|
||||
- SUCCESS
|
||||
|
||||
scsi_finish_command() is invoked for the command. The
|
||||
function does some maintenance chores and then calls
|
||||
scsi_io_completion() to finish the I/O.
|
||||
@@ -66,15 +73,19 @@ with the command.
|
||||
of the data in case of an error.
|
||||
|
||||
- NEEDS_RETRY
|
||||
|
||||
- ADD_TO_MLQUEUE
|
||||
|
||||
scmd is requeued to blk queue.
|
||||
|
||||
- otherwise
|
||||
|
||||
scsi_eh_scmd_add(scmd) is invoked for the command. See
|
||||
[1-3] for details of this function.
|
||||
|
||||
|
||||
[1-2-2] Completing a scmd w/ timeout
|
||||
1.2.2 Completing a scmd w/ timeout
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The timeout handler is scsi_times_out(). When a timeout occurs, this
|
||||
function
|
||||
@@ -101,16 +112,19 @@ function
|
||||
3. scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD) is invoked for the
|
||||
command. See [1-4] for more information.
|
||||
|
||||
[1-3] Asynchronous command aborts
|
||||
1.3 Asynchronous command aborts
|
||||
-------------------------------
|
||||
|
||||
After a timeout occurs a command abort is scheduled from
|
||||
scsi_abort_command(). If the abort is successful the command
|
||||
will either be retried (if the number of retries is not exhausted)
|
||||
or terminated with DID_TIME_OUT.
|
||||
|
||||
Otherwise scsi_eh_scmd_add() is invoked for the command.
|
||||
See [1-4] for more information.
|
||||
|
||||
[1-4] How EH takes over
|
||||
1.4 How EH takes over
|
||||
---------------------
|
||||
|
||||
scmds enter EH via scsi_eh_scmd_add(), which does the following.
|
||||
|
||||
@@ -147,7 +161,8 @@ timer has already expired.
|
||||
forget about - timed out scmds later.
|
||||
|
||||
|
||||
[2] How SCSI EH works
|
||||
2. How SCSI EH works
|
||||
====================
|
||||
|
||||
LLDD's can implement SCSI EH actions in one of the following two
|
||||
ways.
|
||||
@@ -177,9 +192,11 @@ calling scsi_restart_operations(), which
|
||||
4. Kicks queues in all devices on the host in the asses
|
||||
|
||||
|
||||
[2-1] EH through fine-grained callbacks
|
||||
2.1 EH through fine-grained callbacks
|
||||
-------------------------------------
|
||||
|
||||
[2-1-1] Overview
|
||||
2.1.1 Overview
|
||||
^^^^^^^^^^^^^^
|
||||
|
||||
If eh_strategy_handler() is not present, SCSI midlayer takes charge
|
||||
of driving error handling. EH's goals are two - make LLDD, host and
|
||||
@@ -194,6 +211,8 @@ others are performed by invoking one of the following fine-grained
|
||||
hostt EH callbacks. Callbacks may be omitted and omitted ones are
|
||||
considered to fail always.
|
||||
|
||||
::
|
||||
|
||||
int (* eh_abort_handler)(struct scsi_cmnd *);
|
||||
int (* eh_device_reset_handler)(struct scsi_cmnd *);
|
||||
int (* eh_bus_reset_handler)(struct scsi_cmnd *);
|
||||
@@ -232,47 +251,61 @@ EH), REQ_FAILFAST is not set and ++scmd->retries is less than
|
||||
scmd->allowed.
|
||||
|
||||
|
||||
[2-1-2] Flow of scmds through EH
|
||||
2.1.2 Flow of scmds through EH
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
1. Error completion / time out
|
||||
ACTION: scsi_eh_scmd_add() is invoked for scmd
|
||||
|
||||
:ACTION: scsi_eh_scmd_add() is invoked for scmd
|
||||
|
||||
- add scmd to shost->eh_cmd_q
|
||||
- set SHOST_RECOVERY
|
||||
- shost->host_failed++
|
||||
LOCKING: shost->host_lock
|
||||
|
||||
:LOCKING: shost->host_lock
|
||||
|
||||
2. EH starts
|
||||
ACTION: move all scmds to EH's local eh_work_q. shost->eh_cmd_q
|
||||
|
||||
:ACTION: move all scmds to EH's local eh_work_q. shost->eh_cmd_q
|
||||
is cleared.
|
||||
LOCKING: shost->host_lock (not strictly necessary, just for
|
||||
|
||||
:LOCKING: shost->host_lock (not strictly necessary, just for
|
||||
consistency)
|
||||
|
||||
3. scmd recovered
|
||||
ACTION: scsi_eh_finish_cmd() is invoked to EH-finish scmd
|
||||
|
||||
:ACTION: scsi_eh_finish_cmd() is invoked to EH-finish scmd
|
||||
|
||||
- scsi_setup_cmd_retry()
|
||||
- move from local eh_work_q to local eh_done_q
|
||||
LOCKING: none
|
||||
CONCURRENCY: at most one thread per separate eh_work_q to
|
||||
|
||||
:LOCKING: none
|
||||
|
||||
:CONCURRENCY: at most one thread per separate eh_work_q to
|
||||
keep queue manipulation lockless
|
||||
|
||||
4. EH completes
|
||||
ACTION: scsi_eh_flush_done_q() retries scmds or notifies upper
|
||||
|
||||
:ACTION: scsi_eh_flush_done_q() retries scmds or notifies upper
|
||||
layer of failure. May be called concurrently but must have
|
||||
a no more than one thread per separate eh_work_q to
|
||||
manipulate the queue locklessly
|
||||
|
||||
- scmd is removed from eh_done_q and scmd->eh_entry is cleared
|
||||
- if retry is necessary, scmd is requeued using
|
||||
scsi_queue_insert()
|
||||
- otherwise, scsi_finish_command() is invoked for scmd
|
||||
- zero shost->host_failed
|
||||
LOCKING: queue or finish function performs appropriate locking
|
||||
|
||||
:LOCKING: queue or finish function performs appropriate locking
|
||||
|
||||
|
||||
[2-1-3] Flow of control
|
||||
2.1.3 Flow of control
|
||||
^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EH through fine-grained callbacks start from scsi_unjam_host().
|
||||
|
||||
<<scsi_unjam_host>>
|
||||
``scsi_unjam_host``
|
||||
|
||||
1. Lock shost->host_lock, splice_init shost->eh_cmd_q into local
|
||||
eh_work_q and unlock host_lock. Note that shost->eh_cmd_q is
|
||||
@@ -280,7 +313,7 @@ scmd->allowed.
|
||||
|
||||
2. Invoke scsi_eh_get_sense.
|
||||
|
||||
<<scsi_eh_get_sense>>
|
||||
``scsi_eh_get_sense``
|
||||
|
||||
This action is taken for each error-completed
|
||||
(!SCSI_EH_CANCEL_CMD) commands without valid sense data. Most
|
||||
@@ -315,7 +348,7 @@ scmd->allowed.
|
||||
|
||||
3. If !list_empty(&eh_work_q), invoke scsi_eh_abort_cmds().
|
||||
|
||||
<<scsi_eh_abort_cmds>>
|
||||
``scsi_eh_abort_cmds``
|
||||
|
||||
This action is taken for each timed out command when
|
||||
no_async_abort is enabled in the host template.
|
||||
@@ -339,14 +372,14 @@ scmd->allowed.
|
||||
|
||||
4. If !list_empty(&eh_work_q), invoke scsi_eh_ready_devs()
|
||||
|
||||
<<scsi_eh_ready_devs>>
|
||||
``scsi_eh_ready_devs``
|
||||
|
||||
This function takes four increasingly more severe measures to
|
||||
make failed sdevs ready for new commands.
|
||||
|
||||
1. Invoke scsi_eh_stu()
|
||||
|
||||
<<scsi_eh_stu>>
|
||||
``scsi_eh_stu``
|
||||
|
||||
For each sdev which has failed scmds with valid sense data
|
||||
of which scsi_check_sense()'s verdict is FAILED,
|
||||
@@ -369,7 +402,7 @@ scmd->allowed.
|
||||
|
||||
2. If !list_empty(&eh_work_q), invoke scsi_eh_bus_device_reset().
|
||||
|
||||
<<scsi_eh_bus_device_reset>>
|
||||
``scsi_eh_bus_device_reset``
|
||||
|
||||
This action is very similar to scsi_eh_stu() except that,
|
||||
instead of issuing STU, hostt->eh_device_reset_handler()
|
||||
@@ -379,7 +412,7 @@ scmd->allowed.
|
||||
|
||||
3. If !list_empty(&eh_work_q), invoke scsi_eh_bus_reset()
|
||||
|
||||
<<scsi_eh_bus_reset>>
|
||||
``scsi_eh_bus_reset``
|
||||
|
||||
hostt->eh_bus_reset_handler() is invoked for each channel
|
||||
with failed scmds. If bus reset succeeds, all failed
|
||||
@@ -388,7 +421,7 @@ scmd->allowed.
|
||||
|
||||
4. If !list_empty(&eh_work_q), invoke scsi_eh_host_reset()
|
||||
|
||||
<<scsi_eh_host_reset>>
|
||||
``scsi_eh_host_reset``
|
||||
|
||||
This is the last resort. hostt->eh_host_reset_handler()
|
||||
is invoked. If host reset succeeds, all failed scmds on
|
||||
@@ -396,14 +429,14 @@ scmd->allowed.
|
||||
|
||||
5. If !list_empty(&eh_work_q), invoke scsi_eh_offline_sdevs()
|
||||
|
||||
<<scsi_eh_offline_sdevs>>
|
||||
``scsi_eh_offline_sdevs``
|
||||
|
||||
Take all sdevs which still have unrecovered scmds offline
|
||||
and EH-finish the scmds.
|
||||
|
||||
5. Invoke scsi_eh_flush_done_q().
|
||||
|
||||
<<scsi_eh_flush_done_q>>
|
||||
``scsi_eh_flush_done_q``
|
||||
|
||||
At this point all scmds are recovered (or given up) and
|
||||
put on eh_done_q by scsi_eh_finish_cmd(). This function
|
||||
@@ -411,7 +444,8 @@ scmd->allowed.
|
||||
layer of failure of the scmds.
|
||||
|
||||
|
||||
[2-2] EH through transportt->eh_strategy_handler()
|
||||
2.2 EH through transportt->eh_strategy_handler()
|
||||
------------------------------------------------
|
||||
|
||||
transportt->eh_strategy_handler() is invoked in the place of
|
||||
scsi_unjam_host() and it is responsible for whole recovery process.
|
||||
@@ -422,7 +456,8 @@ SCSI midlayer. IOW, of the steps described in [2-1-2], all steps
|
||||
except for #1 must be implemented by eh_strategy_handler().
|
||||
|
||||
|
||||
[2-2-1] Pre transportt->eh_strategy_handler() SCSI midlayer conditions
|
||||
2.2.1 Pre transportt->eh_strategy_handler() SCSI midlayer conditions
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The following conditions are true on entry to the handler.
|
||||
|
||||
@@ -435,7 +470,8 @@ except for #1 must be implemented by eh_strategy_handler().
|
||||
- shost->host_failed == shost->host_busy
|
||||
|
||||
|
||||
[2-2-2] Post transportt->eh_strategy_handler() SCSI midlayer conditions
|
||||
2.2.2 Post transportt->eh_strategy_handler() SCSI midlayer conditions
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The following conditions must be true on exit from the handler.
|
||||
|
||||
@@ -453,7 +489,8 @@ except for #1 must be implemented by eh_strategy_handler().
|
||||
->allowed to limit the number of retries.
|
||||
|
||||
|
||||
[2-2-3] Things to consider
|
||||
2.2.3 Things to consider
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
- Know that timed out scmds are still active on lower layers. Make
|
||||
lower layers forget about them before doing anything else with
|
||||
@@ -469,7 +506,7 @@ except for #1 must be implemented by eh_strategy_handler().
|
||||
offline.
|
||||
|
||||
|
||||
--
|
||||
Tejun Heo
|
||||
htejun@gmail.com
|
||||
|
||||
11th September 2005
|
||||
Reference in New Issue
Block a user