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scsi: fix race between simultaneous decrements of ->host_failed 

sas_ata_strategy_handler() adds the works of the ata error handler to
system_unbound_wq. This workqueue asynchronously runs work items, so the
ata error handler will be performed concurrently on different CPUs. In
this case, ->host_failed will be decreased simultaneously in
scsi_eh_finish_cmd() on different CPUs, and become abnormal.

It will lead to permanently inequality between ->host_failed and
->host_busy, and scsi error handler thread won't start running. IO
errors after that won't be handled.

Since all scmds must have been handled in the strategy handler, just
remove the decrement in scsi_eh_finish_cmd() and zero ->host_busy after
the strategy handler to fix this race.

Fixes: 50824d6c56 ("[SCSI] libsas: async ata-eh")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <fangwei1@huawei.com>
Reviewed-by: James Bottomley <jejb@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Wei Fang 2016-06-07 14:53:56 +08:00 committed by Martin K. Petersen
parent 6b7e9cde49
commit 72d8c36ec3
3 changed files with 10 additions and 4 deletions
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8
Documentation/scsi/scsi_eh.txt
View File

@ -263,19 +263,23 @@ scmd->allowed.
3. scmd recovered 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
- shost->host_failed--
- clear scmd->eh_eflags - clear scmd->eh_eflags
- scsi_setup_cmd_retry() - scsi_setup_cmd_retry()
- move from local eh_work_q to local eh_done_q - move from local eh_work_q to local eh_done_q
LOCKING: none LOCKING: none
CONCURRENCY: at most one thread per separate eh_work_q to
keep queue manipulation lockless
4. EH completes 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. 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 - scmd is removed from eh_done_q and scmd->eh_entry is cleared
- if retry is necessary, scmd is requeued using - if retry is necessary, scmd is requeued using
scsi_queue_insert() scsi_queue_insert()
- otherwise, scsi_finish_command() is invoked for scmd - 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
drivers/ata/libata-eh.c
View File

@ -606,7 +606,7 @@ void ata_scsi_error(struct Scsi_Host *host)
ata_scsi_port_error_handler(host, ap); ata_scsi_port_error_handler(host, ap);
/* finish or retry handled scmd's and clean up */ /* finish or retry handled scmd's and clean up */
WARN_ON(host->host_failed || !list_empty(&eh_work_q)); WARN_ON(!list_empty(&eh_work_q));
DPRINTK("EXIT\n"); DPRINTK("EXIT\n");
} }

4
drivers/scsi/scsi_error.c
View File

@ -1127,7 +1127,6 @@ static int scsi_eh_action(struct scsi_cmnd *scmd, int rtn)
*/ */
void scsi_eh_finish_cmd(struct scsi_cmnd *scmd, struct list_head *done_q) void scsi_eh_finish_cmd(struct scsi_cmnd *scmd, struct list_head *done_q)
{ {
scmd->device->host->host_failed--;
scmd->eh_eflags = 0; scmd->eh_eflags = 0;
list_move_tail(&scmd->eh_entry, done_q); list_move_tail(&scmd->eh_entry, done_q);
} }
@ -2226,6 +2225,9 @@ int scsi_error_handler(void *data)
else else
scsi_unjam_host(shost); scsi_unjam_host(shost);
/* All scmds have been handled */
shost->host_failed = 0;
/* /*
* Note - if the above fails completely, the action is to take * Note - if the above fails completely, the action is to take
* individual devices offline and flush the queue of any * individual devices offline and flush the queue of any