diff options
Diffstat (limited to 'Documentation/scsi/scsi_eh.txt')
| -rw-r--r-- | Documentation/scsi/scsi_eh.txt | 69 |
1 files changed, 39 insertions, 30 deletions
diff --git a/Documentation/scsi/scsi_eh.txt b/Documentation/scsi/scsi_eh.txt index 6ff16b620d84..a0c85110a07e 100644 --- a/Documentation/scsi/scsi_eh.txt +++ b/Documentation/scsi/scsi_eh.txt @@ -42,20 +42,14 @@ discussion. 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 SCSI midlayer will time it out. +invoking hostt->queuecommand() or the block layer will time it out. [1-2-1] Completing a scmd w/ scsi_done For all non-EH commands, scsi_done() is the completion callback. It -does the following. - - 1. Delete timeout timer. If it fails, it means that timeout timer - has expired and is going to finish the command. Just return. - - 2. Link scmd to per-cpu scsi_done_q using scmd->en_entry - - 3. Raise SCSI_SOFTIRQ +just calls blk_complete_request() to delete the block layer timer and +raise SCSI_SOFTIRQ SCSI_SOFTIRQ handler scsi_softirq calls scsi_decide_disposition() to determine what to do with the command. scsi_decide_disposition() @@ -64,10 +58,12 @@ with the command. - SUCCESS scsi_finish_command() is invoked for the command. The - function does some maintenance choirs and notify completion by - calling scmd->done() callback, which, for fs requests, would - be HLD completion callback - sd:sd_rw_intr, sr:rw_intr, - st:st_intr. + function does some maintenance chores and then calls + scsi_io_completion() to finish the I/O. + scsi_io_completion() then notifies the block layer on + the completed request by calling blk_end_request and + friends or figures out what to do with the remainder + of the data in case of an error. - NEEDS_RETRY - ADD_TO_MLQUEUE @@ -86,33 +82,45 @@ function 1. invokes optional hostt->eh_timed_out() callback. Return value can be one of - - EH_HANDLED - This indicates that eh_timed_out() dealt with the timeout. The - scmd is passed to __scsi_done() and thus linked into per-cpu - scsi_done_q. Normal command completion described in [1-2-1] - follows. + - BLK_EH_HANDLED + This indicates that eh_timed_out() dealt with the timeout. + The command is passed back to the block layer and completed + via __blk_complete_requests(). + + *NOTE* After returning BLK_EH_HANDLED the SCSI layer is + assumed to be finished with the command, and no other + functions from the SCSI layer will be called. So this + should typically only be returned if the eh_timed_out() + handler raced with normal completion. - - EH_RESET_TIMER + - BLK_EH_RESET_TIMER This indicates that more time is required to finish the command. Timer is restarted. This action is counted as a retry and only allowed scmd->allowed + 1(!) times. Once the - limit is reached, action for EH_NOT_HANDLED is taken instead. + limit is reached, action for BLK_EH_NOT_HANDLED is taken instead. - *NOTE* This action is racy as the LLDD could finish the scmd - after the timeout has expired but before it's added back. In - such cases, scsi_done() would think that timeout has occurred - and return without doing anything. We lose completion and the - command will time out again. - - - EH_NOT_HANDLED - This is the same as when eh_timed_out() callback doesn't exist. + - BLK_EH_NOT_HANDLED + eh_timed_out() callback did not handle the command. Step #2 is taken. + 2. If the host supports asynchronous completion (as indicated by the + no_async_abort setting in the host template) scsi_abort_command() + is invoked to schedule an asynchrous abort. If that fails + Step #3 is taken. + 2. scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD) is invoked for the command. See [1-3] for more information. +[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. -[1-3] How EH takes over +[1-4] How EH takes over scmds enter EH via scsi_eh_scmd_add(), which does the following. @@ -320,7 +328,8 @@ scmd->allowed. <<scsi_eh_abort_cmds>> - This action is taken for each timed out command. + This action is taken for each timed out command when + no_async_abort is enabled in the host template. hostt->eh_abort_handler() is invoked for each scmd. The handler returns SUCCESS if it has succeeded to make LLDD and all related hardware forget about the scmd. |