Commit 72d8c36e authored by Wei Fang's avatar Wei Fang Committed by Martin K. Petersen
Browse files

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: 50824d6c ("[SCSI] libsas: async ata-eh")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarWei Fang <fangwei1@huawei.com>
Reviewed-by: default avatarJames Bottomley <jejb@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 6b7e9cde

Documentation/scsi/scsi_eh.txt

+6 −2
Original line number Diff line number Diff line
@@ -263,19 +263,23 @@ scmd->allowed. 


 3. scmd recovered

    ACTION: scsi_eh_finish_cmd() is invoked to EH-finish scmd

	- shost->host_failed--

	- clear scmd->eh_eflags

	- 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

		 keep queue manipulation lockless



 4. EH completes

    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

	- 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

drivers/ata/libata-eh.c

+1 −1
Original line number Diff line number Diff line
@@ -606,7 +606,7 @@ void ata_scsi_error(struct Scsi_Host *host) 
	ata_scsi_port_error_handler(host, ap);



	/* 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");

}

drivers/scsi/scsi_error.c

+3 −1
Original line number Diff line number Diff line
@@ -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)

{

	scmd->device->host->host_failed--;

	scmd->eh_eflags = 0;

	list_move_tail(&scmd->eh_entry, done_q);

}
@@ -2226,6 +2225,9 @@ int scsi_error_handler(void *data) 
		else

			scsi_unjam_host(shost);



		/* All scmds have been handled */

		shost->host_failed = 0;



		/*

		 * Note - if the above fails completely, the action is to take

		 * individual devices offline and flush the queue of any

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