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e513de99 | 1 | .. SPDX-License-Identifier: GPL-2.0 |
70c83e11 | 2 | |
e513de99 | 3 | ======= |
70c83e11 | 4 | SCSI EH |
e513de99 | 5 | ======= |
70c83e11 | 6 | |
e513de99 | 7 | This document describes SCSI midlayer error handling infrastructure. |
ce5c5d65 | 8 | Please refer to Documentation/scsi/scsi_mid_low_api.rst for more |
70c83e11 TH |
9 | information regarding SCSI midlayer. |
10 | ||
e513de99 | 11 | .. TABLE OF CONTENTS |
70c83e11 | 12 | |
e513de99 MCC |
13 | [1] How SCSI commands travel through the midlayer and to EH |
14 | [1-1] struct scsi_cmnd | |
15 | [1-2] How do scmd's get completed? | |
16 | [1-2-1] Completing a scmd w/ scsi_done | |
17 | [1-2-2] Completing a scmd w/ timeout | |
18 | [1-3] How EH takes over | |
19 | [2] How SCSI EH works | |
20 | [2-1] EH through fine-grained callbacks | |
21 | [2-1-1] Overview | |
22 | [2-1-2] Flow of scmds through EH | |
23 | [2-1-3] Flow of control | |
24 | [2-2] EH through transportt->eh_strategy_handler() | |
25 | [2-2-1] Pre transportt->eh_strategy_handler() SCSI midlayer conditions | |
26 | [2-2-2] Post transportt->eh_strategy_handler() SCSI midlayer conditions | |
27 | [2-2-3] Things to consider | |
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28 | |
29 | ||
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30 | 1. How SCSI commands travel through the midlayer and to EH |
31 | ========================================================== | |
70c83e11 | 32 | |
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33 | 1.1 struct scsi_cmnd |
34 | -------------------- | |
70c83e11 | 35 | |
e513de99 | 36 | Each SCSI command is represented with struct scsi_cmnd (== scmd). A |
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37 | scmd has two list_head's to link itself into lists. The two are |
38 | scmd->list and scmd->eh_entry. The former is used for free list or | |
39 | per-device allocated scmd list and not of much interest to this EH | |
40 | discussion. The latter is used for completion and EH lists and unless | |
41 | otherwise stated scmds are always linked using scmd->eh_entry in this | |
42 | discussion. | |
43 | ||
44 | ||
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45 | 1.2 How do scmd's get completed? |
46 | -------------------------------- | |
70c83e11 | 47 | |
e513de99 | 48 | Once LLDD gets hold of a scmd, either the LLDD will complete the |
70c83e11 | 49 | command by calling scsi_done callback passed from midlayer when |
6ad55502 | 50 | invoking hostt->queuecommand() or the block layer will time it out. |
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51 | |
52 | ||
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53 | 1.2.1 Completing a scmd w/ scsi_done |
54 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 | 55 | |
e513de99 | 56 | For all non-EH commands, scsi_done() is the completion callback. It |
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57 | just calls blk_complete_request() to delete the block layer timer and |
58 | raise SCSI_SOFTIRQ | |
70c83e11 | 59 | |
e513de99 | 60 | SCSI_SOFTIRQ handler scsi_softirq calls scsi_decide_disposition() to |
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61 | determine what to do with the command. scsi_decide_disposition() |
62 | looks at the scmd->result value and sense data to determine what to do | |
63 | with the command. | |
64 | ||
65 | - SUCCESS | |
e513de99 | 66 | |
70c83e11 | 67 | scsi_finish_command() is invoked for the command. The |
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68 | function does some maintenance chores and then calls |
69 | scsi_io_completion() to finish the I/O. | |
70 | scsi_io_completion() then notifies the block layer on | |
71 | the completed request by calling blk_end_request and | |
72 | friends or figures out what to do with the remainder | |
73 | of the data in case of an error. | |
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74 | |
75 | - NEEDS_RETRY | |
e513de99 | 76 | |
70c83e11 | 77 | - ADD_TO_MLQUEUE |
e513de99 | 78 | |
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79 | scmd is requeued to blk queue. |
80 | ||
81 | - otherwise | |
e513de99 | 82 | |
a0658632 | 83 | scsi_eh_scmd_add(scmd) is invoked for the command. See |
5d3f083d | 84 | [1-3] for details of this function. |
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85 | |
86 | ||
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87 | 1.2.2 Completing a scmd w/ timeout |
88 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 | 89 | |
deef1be1 | 90 | The timeout handler is scsi_timeout(). When a timeout occurs, this function |
70c83e11 | 91 | |
8c0ae656 | 92 | 1. invokes optional hostt->eh_timed_out() callback. Return value can |
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93 | be one of |
94 | ||
6ad55502 | 95 | - BLK_EH_RESET_TIMER |
70c83e11 | 96 | This indicates that more time is required to finish the |
5c139ce9 | 97 | command. Timer is restarted. |
70c83e11 | 98 | |
6600593c | 99 | - BLK_EH_DONE |
6ad55502 | 100 | eh_timed_out() callback did not handle the command. |
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101 | Step #2 is taken. |
102 | ||
5c139ce9 KK |
103 | 2. scsi_abort_command() is invoked to schedule an asynchronous abort which may |
104 | issue a retry scmd->allowed + 1 times. Asynchronous aborts are not invoked | |
105 | for commands for which the SCSI_EH_ABORT_SCHEDULED flag is set (this | |
106 | indicates that the command already had been aborted once, and this is a | |
107 | retry which failed), when retries are exceeded, or when the EH deadline is | |
108 | expired. In these cases Step #3 is taken. | |
6ad55502 | 109 | |
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110 | 3. scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD) is invoked for the |
111 | command. See [1-4] for more information. | |
70c83e11 | 112 | |
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113 | 1.3 Asynchronous command aborts |
114 | ------------------------------- | |
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115 | |
116 | After a timeout occurs a command abort is scheduled from | |
117 | scsi_abort_command(). If the abort is successful the command | |
118 | will either be retried (if the number of retries is not exhausted) | |
119 | or terminated with DID_TIME_OUT. | |
e513de99 | 120 | |
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121 | Otherwise scsi_eh_scmd_add() is invoked for the command. |
122 | See [1-4] for more information. | |
70c83e11 | 123 | |
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124 | 1.4 How EH takes over |
125 | --------------------- | |
70c83e11 | 126 | |
e513de99 | 127 | scmds enter EH via scsi_eh_scmd_add(), which does the following. |
70c83e11 | 128 | |
a0658632 | 129 | 1. Links scmd->eh_entry to shost->eh_cmd_q |
70c83e11 | 130 | |
a0658632 | 131 | 2. Sets SHOST_RECOVERY bit in shost->shost_state |
70c83e11 | 132 | |
a0658632 | 133 | 3. Increments shost->host_failed |
70c83e11 | 134 | |
a0658632 | 135 | 4. Wakes up SCSI EH thread if shost->host_busy == shost->host_failed |
70c83e11 | 136 | |
e513de99 | 137 | As can be seen above, once any scmd is added to shost->eh_cmd_q, |
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138 | SHOST_RECOVERY shost_state bit is turned on. This prevents any new |
139 | scmd to be issued from blk queue to the host; eventually, all scmds on | |
140 | the host either complete normally, fail and get added to eh_cmd_q, or | |
141 | time out and get added to shost->eh_cmd_q. | |
142 | ||
e513de99 | 143 | If all scmds either complete or fail, the number of in-flight scmds |
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144 | becomes equal to the number of failed scmds - i.e. shost->host_busy == |
145 | shost->host_failed. This wakes up SCSI EH thread. So, once woken up, | |
146 | SCSI EH thread can expect that all in-flight commands have failed and | |
147 | are linked on shost->eh_cmd_q. | |
148 | ||
e513de99 | 149 | Note that this does not mean lower layers are quiescent. If a LLDD |
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150 | completed a scmd with error status, the LLDD and lower layers are |
151 | assumed to forget about the scmd at that point. However, if a scmd | |
8c0ae656 | 152 | has timed out, unless hostt->eh_timed_out() made lower layers forget |
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153 | about the scmd, which currently no LLDD does, the command is still |
154 | active as long as lower layers are concerned and completion could | |
155 | occur at any time. Of course, all such completions are ignored as the | |
156 | timer has already expired. | |
157 | ||
e513de99 | 158 | We'll talk about how SCSI EH takes actions to abort - make LLDD |
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159 | forget about - timed out scmds later. |
160 | ||
161 | ||
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162 | 2. How SCSI EH works |
163 | ==================== | |
70c83e11 | 164 | |
e513de99 | 165 | LLDD's can implement SCSI EH actions in one of the following two |
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166 | ways. |
167 | ||
168 | - Fine-grained EH callbacks | |
169 | LLDD can implement fine-grained EH callbacks and let SCSI | |
170 | midlayer drive error handling and call appropriate callbacks. | |
fff9289b | 171 | This will be discussed further in [2-1]. |
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172 | |
173 | - eh_strategy_handler() callback | |
174 | This is one big callback which should perform whole error | |
542cb459 | 175 | handling. As such, it should do all chores the SCSI midlayer |
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176 | performs during recovery. This will be discussed in [2-2]. |
177 | ||
e513de99 | 178 | Once recovery is complete, SCSI EH resumes normal operation by |
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179 | calling scsi_restart_operations(), which |
180 | ||
181 | 1. Checks if door locking is needed and locks door. | |
182 | ||
183 | 2. Clears SHOST_RECOVERY shost_state bit | |
184 | ||
185 | 3. Wakes up waiters on shost->host_wait. This occurs if someone | |
186 | calls scsi_block_when_processing_errors() on the host. | |
187 | (*QUESTION* why is it needed? All operations will be blocked | |
188 | anyway after it reaches blk queue.) | |
189 | ||
190 | 4. Kicks queues in all devices on the host in the asses | |
191 | ||
192 | ||
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193 | 2.1 EH through fine-grained callbacks |
194 | ------------------------------------- | |
70c83e11 | 195 | |
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196 | 2.1.1 Overview |
197 | ^^^^^^^^^^^^^^ | |
70c83e11 | 198 | |
e513de99 | 199 | If eh_strategy_handler() is not present, SCSI midlayer takes charge |
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200 | of driving error handling. EH's goals are two - make LLDD, host and |
201 | device forget about timed out scmds and make them ready for new | |
202 | commands. A scmd is said to be recovered if the scmd is forgotten by | |
203 | lower layers and lower layers are ready to process or fail the scmd | |
204 | again. | |
205 | ||
e513de99 | 206 | To achieve these goals, EH performs recovery actions with increasing |
2fe0ae78 | 207 | severity. Some actions are performed by issuing SCSI commands and |
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208 | others are performed by invoking one of the following fine-grained |
209 | hostt EH callbacks. Callbacks may be omitted and omitted ones are | |
210 | considered to fail always. | |
211 | ||
e513de99 | 212 | :: |
70c83e11 | 213 | |
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214 | int (* eh_abort_handler)(struct scsi_cmnd *); |
215 | int (* eh_device_reset_handler)(struct scsi_cmnd *); | |
216 | int (* eh_bus_reset_handler)(struct scsi_cmnd *); | |
217 | int (* eh_host_reset_handler)(struct scsi_cmnd *); | |
218 | ||
219 | Higher-severity actions are taken only when lower-severity actions | |
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220 | cannot recover some of failed scmds. Also, note that failure of the |
221 | highest-severity action means EH failure and results in offlining of | |
222 | all unrecovered devices. | |
223 | ||
e513de99 | 224 | During recovery, the following rules are followed |
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225 | |
226 | - Recovery actions are performed on failed scmds on the to do list, | |
227 | eh_work_q. If a recovery action succeeds for a scmd, recovered | |
228 | scmds are removed from eh_work_q. | |
229 | ||
230 | Note that single recovery action on a scmd can recover multiple | |
231 | scmds. e.g. resetting a device recovers all failed scmds on the | |
232 | device. | |
233 | ||
234 | - Higher severity actions are taken iff eh_work_q is not empty after | |
235 | lower severity actions are complete. | |
236 | ||
237 | - EH reuses failed scmds to issue commands for recovery. For | |
238 | timed-out scmds, SCSI EH ensures that LLDD forgets about a scmd | |
239 | before reusing it for EH commands. | |
240 | ||
e513de99 | 241 | When a scmd is recovered, the scmd is moved from eh_work_q to EH |
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242 | local eh_done_q using scsi_eh_finish_cmd(). After all scmds are |
243 | recovered (eh_work_q is empty), scsi_eh_flush_done_q() is invoked to | |
244 | either retry or error-finish (notify upper layer of failure) recovered | |
245 | scmds. | |
246 | ||
e513de99 | 247 | scmds are retried iff its sdev is still online (not offlined during |
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248 | EH), REQ_FAILFAST is not set and ++scmd->retries is less than |
249 | scmd->allowed. | |
250 | ||
251 | ||
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252 | 2.1.2 Flow of scmds through EH |
253 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
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254 | |
255 | 1. Error completion / time out | |
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256 | |
257 | :ACTION: scsi_eh_scmd_add() is invoked for scmd | |
258 | ||
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259 | - add scmd to shost->eh_cmd_q |
260 | - set SHOST_RECOVERY | |
261 | - shost->host_failed++ | |
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262 | |
263 | :LOCKING: shost->host_lock | |
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264 | |
265 | 2. EH starts | |
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266 | |
267 | :ACTION: move all scmds to EH's local eh_work_q. shost->eh_cmd_q | |
268 | is cleared. | |
269 | ||
270 | :LOCKING: shost->host_lock (not strictly necessary, just for | |
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271 | consistency) |
272 | ||
273 | 3. scmd recovered | |
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274 | |
275 | :ACTION: scsi_eh_finish_cmd() is invoked to EH-finish scmd | |
276 | ||
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277 | - scsi_setup_cmd_retry() |
278 | - move from local eh_work_q to local eh_done_q | |
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279 | |
280 | :LOCKING: none | |
281 | ||
282 | :CONCURRENCY: at most one thread per separate eh_work_q to | |
283 | keep queue manipulation lockless | |
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284 | |
285 | 4. EH completes | |
70c83e11 | 286 | |
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287 | :ACTION: scsi_eh_flush_done_q() retries scmds or notifies upper |
288 | layer of failure. May be called concurrently but must have | |
289 | a no more than one thread per separate eh_work_q to | |
290 | manipulate the queue locklessly | |
70c83e11 | 291 | |
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292 | - scmd is removed from eh_done_q and scmd->eh_entry is cleared |
293 | - if retry is necessary, scmd is requeued using | |
294 | scsi_queue_insert() | |
295 | - otherwise, scsi_finish_command() is invoked for scmd | |
296 | - zero shost->host_failed | |
297 | ||
298 | :LOCKING: queue or finish function performs appropriate locking | |
299 | ||
300 | ||
301 | 2.1.3 Flow of control | |
302 | ^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 TH |
303 | |
304 | EH through fine-grained callbacks start from scsi_unjam_host(). | |
305 | ||
e513de99 | 306 | ``scsi_unjam_host`` |
70c83e11 TH |
307 | |
308 | 1. Lock shost->host_lock, splice_init shost->eh_cmd_q into local | |
309 | eh_work_q and unlock host_lock. Note that shost->eh_cmd_q is | |
310 | cleared by this action. | |
311 | ||
312 | 2. Invoke scsi_eh_get_sense. | |
313 | ||
e513de99 | 314 | ``scsi_eh_get_sense`` |
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315 | |
316 | This action is taken for each error-completed | |
317 | (!SCSI_EH_CANCEL_CMD) commands without valid sense data. Most | |
318 | SCSI transports/LLDDs automatically acquire sense data on | |
319 | command failures (autosense). Autosense is recommended for | |
320 | performance reasons and as sense information could get out of | |
25985edc | 321 | sync between occurrence of CHECK CONDITION and this action. |
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322 | |
323 | Note that if autosense is not supported, scmd->sense_buffer | |
324 | contains invalid sense data when error-completing the scmd | |
325 | with scsi_done(). scsi_decide_disposition() always returns | |
326 | FAILED in such cases thus invoking SCSI EH. When the scmd | |
327 | reaches here, sense data is acquired and | |
328 | scsi_decide_disposition() is called again. | |
329 | ||
330 | 1. Invoke scsi_request_sense() which issues REQUEST_SENSE | |
331 | command. If fails, no action. Note that taking no action | |
332 | causes higher-severity recovery to be taken for the scmd. | |
333 | ||
334 | 2. Invoke scsi_decide_disposition() on the scmd | |
335 | ||
336 | - SUCCESS | |
337 | scmd->retries is set to scmd->allowed preventing | |
338 | scsi_eh_flush_done_q() from retrying the scmd and | |
339 | scsi_eh_finish_cmd() is invoked. | |
340 | ||
341 | - NEEDS_RETRY | |
342 | scsi_eh_finish_cmd() invoked | |
343 | ||
344 | - otherwise | |
345 | No action. | |
346 | ||
347 | 3. If !list_empty(&eh_work_q), invoke scsi_eh_abort_cmds(). | |
348 | ||
e513de99 | 349 | ``scsi_eh_abort_cmds`` |
70c83e11 | 350 | |
6ad55502 HR |
351 | This action is taken for each timed out command when |
352 | no_async_abort is enabled in the host template. | |
70c83e11 TH |
353 | hostt->eh_abort_handler() is invoked for each scmd. The |
354 | handler returns SUCCESS if it has succeeded to make LLDD and | |
355 | all related hardware forget about the scmd. | |
356 | ||
357 | If a timedout scmd is successfully aborted and the sdev is | |
358 | either offline or ready, scsi_eh_finish_cmd() is invoked for | |
359 | the scmd. Otherwise, the scmd is left in eh_work_q for | |
360 | higher-severity actions. | |
361 | ||
362 | Note that both offline and ready status mean that the sdev is | |
363 | ready to process new scmds, where processing also implies | |
364 | immediate failing; thus, if a sdev is in one of the two | |
365 | states, no further recovery action is needed. | |
366 | ||
367 | Device readiness is tested using scsi_eh_tur() which issues | |
368 | TEST_UNIT_READY command. Note that the scmd must have been | |
369 | aborted successfully before reusing it for TEST_UNIT_READY. | |
370 | ||
371 | 4. If !list_empty(&eh_work_q), invoke scsi_eh_ready_devs() | |
372 | ||
e513de99 | 373 | ``scsi_eh_ready_devs`` |
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374 | |
375 | This function takes four increasingly more severe measures to | |
376 | make failed sdevs ready for new commands. | |
377 | ||
378 | 1. Invoke scsi_eh_stu() | |
379 | ||
e513de99 | 380 | ``scsi_eh_stu`` |
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381 | |
382 | For each sdev which has failed scmds with valid sense data | |
383 | of which scsi_check_sense()'s verdict is FAILED, | |
384 | START_STOP_UNIT command is issued w/ start=1. Note that | |
385 | as we explicitly choose error-completed scmds, it is known | |
386 | that lower layers have forgotten about the scmd and we can | |
387 | reuse it for STU. | |
388 | ||
389 | If STU succeeds and the sdev is either offline or ready, | |
390 | all failed scmds on the sdev are EH-finished with | |
391 | scsi_eh_finish_cmd(). | |
392 | ||
393 | *NOTE* If hostt->eh_abort_handler() isn't implemented or | |
394 | failed, we may still have timed out scmds at this point | |
395 | and STU doesn't make lower layers forget about those | |
396 | scmds. Yet, this function EH-finish all scmds on the sdev | |
397 | if STU succeeds leaving lower layers in an inconsistent | |
398 | state. It seems that STU action should be taken only when | |
399 | a sdev has no timed out scmd. | |
400 | ||
401 | 2. If !list_empty(&eh_work_q), invoke scsi_eh_bus_device_reset(). | |
402 | ||
e513de99 | 403 | ``scsi_eh_bus_device_reset`` |
70c83e11 TH |
404 | |
405 | This action is very similar to scsi_eh_stu() except that, | |
406 | instead of issuing STU, hostt->eh_device_reset_handler() | |
407 | is used. Also, as we're not issuing SCSI commands and | |
408 | resetting clears all scmds on the sdev, there is no need | |
409 | to choose error-completed scmds. | |
410 | ||
411 | 3. If !list_empty(&eh_work_q), invoke scsi_eh_bus_reset() | |
412 | ||
e513de99 | 413 | ``scsi_eh_bus_reset`` |
70c83e11 TH |
414 | |
415 | hostt->eh_bus_reset_handler() is invoked for each channel | |
416 | with failed scmds. If bus reset succeeds, all failed | |
417 | scmds on all ready or offline sdevs on the channel are | |
418 | EH-finished. | |
419 | ||
420 | 4. If !list_empty(&eh_work_q), invoke scsi_eh_host_reset() | |
421 | ||
e513de99 | 422 | ``scsi_eh_host_reset`` |
70c83e11 TH |
423 | |
424 | This is the last resort. hostt->eh_host_reset_handler() | |
425 | is invoked. If host reset succeeds, all failed scmds on | |
426 | all ready or offline sdevs on the host are EH-finished. | |
427 | ||
428 | 5. If !list_empty(&eh_work_q), invoke scsi_eh_offline_sdevs() | |
429 | ||
e513de99 | 430 | ``scsi_eh_offline_sdevs`` |
70c83e11 TH |
431 | |
432 | Take all sdevs which still have unrecovered scmds offline | |
433 | and EH-finish the scmds. | |
434 | ||
435 | 5. Invoke scsi_eh_flush_done_q(). | |
436 | ||
e513de99 | 437 | ``scsi_eh_flush_done_q`` |
70c83e11 TH |
438 | |
439 | At this point all scmds are recovered (or given up) and | |
440 | put on eh_done_q by scsi_eh_finish_cmd(). This function | |
441 | flushes eh_done_q by either retrying or notifying upper | |
442 | layer of failure of the scmds. | |
443 | ||
444 | ||
e513de99 MCC |
445 | 2.2 EH through transportt->eh_strategy_handler() |
446 | ------------------------------------------------ | |
70c83e11 | 447 | |
e513de99 | 448 | transportt->eh_strategy_handler() is invoked in the place of |
70c83e11 TH |
449 | scsi_unjam_host() and it is responsible for whole recovery process. |
450 | On completion, the handler should have made lower layers forget about | |
451 | all failed scmds and either ready for new commands or offline. Also, | |
542cb459 | 452 | it should perform SCSI EH maintenance chores to maintain integrity of |
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453 | SCSI midlayer. IOW, of the steps described in [2-1-2], all steps |
454 | except for #1 must be implemented by eh_strategy_handler(). | |
455 | ||
456 | ||
e513de99 MCC |
457 | 2.2.1 Pre transportt->eh_strategy_handler() SCSI midlayer conditions |
458 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 TH |
459 | |
460 | The following conditions are true on entry to the handler. | |
461 | ||
462 | - Each failed scmd's eh_flags field is set appropriately. | |
463 | ||
464 | - Each failed scmd is linked on scmd->eh_cmd_q by scmd->eh_entry. | |
465 | ||
466 | - SHOST_RECOVERY is set. | |
467 | ||
468 | - shost->host_failed == shost->host_busy | |
469 | ||
470 | ||
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471 | 2.2.2 Post transportt->eh_strategy_handler() SCSI midlayer conditions |
472 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 TH |
473 | |
474 | The following conditions must be true on exit from the handler. | |
475 | ||
476 | - shost->host_failed is zero. | |
477 | ||
70c83e11 TH |
478 | - Each scmd is in such a state that scsi_setup_cmd_retry() on the |
479 | scmd doesn't make any difference. | |
480 | ||
481 | - shost->eh_cmd_q is cleared. | |
482 | ||
483 | - Each scmd->eh_entry is cleared. | |
484 | ||
485 | - Either scsi_queue_insert() or scsi_finish_command() is called on | |
486 | each scmd. Note that the handler is free to use scmd->retries and | |
487 | ->allowed to limit the number of retries. | |
488 | ||
489 | ||
e513de99 MCC |
490 | 2.2.3 Things to consider |
491 | ^^^^^^^^^^^^^^^^^^^^^^^^ | |
70c83e11 TH |
492 | |
493 | - Know that timed out scmds are still active on lower layers. Make | |
494 | lower layers forget about them before doing anything else with | |
495 | those scmds. | |
496 | ||
497 | - For consistency, when accessing/modifying shost data structure, | |
498 | grab shost->host_lock. | |
499 | ||
500 | - On completion, each failed sdev must have forgotten about all | |
501 | active scmds. | |
502 | ||
503 | - On completion, each failed sdev must be ready for new commands or | |
504 | offline. | |
505 | ||
506 | ||
70c83e11 TH |
507 | Tejun Heo |
508 | htejun@gmail.com | |
e513de99 | 509 | |
70c83e11 | 510 | 11th September 2005 |