Re: [PATCH 1/3] Remove two cancel_delayed_work() calls from the error handler

[Hannes Reinecke <hare@suse.de>]

On 05/26/2014 05:14 PM, Bart Van Assche wrote:
> scsi_put_command() is either invoked before a command is queued or
> after a command has completed. scsi_cmnd.abort_work is scheduled
> after a command has timed out and before it is finished. The block
> layer guarantees that either the softirq_done_fn() or the
> rq_timed_out_fn() function is invoked but not both. This means that
> scsi_put_command() is never invoked while abort_work is scheduled.
> Hence remove the cancel_delayed_work() call from scsi_put_command().
>
> Similarly, scsi_abort_command() is only invoked from the SCSI
> timeout handler. If scsi_abort_command() is invoked for a SCSI
> command with the SCSI_EH_ABORT_SCHEDULED flag set this means that
> scmd_eh_abort_handler() has already invoked scsi_queue_insert() and
> hence that scsi_cmnd.abort_work is no longer pending. Hence also
> remove the cancel_delayed_work() call from scsi_abort_command().
>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Jens Axboe <axboe@fb.com>
> Cc: Joe Lawrence <joe.lawrence@stratus.com>
> ---
>   drivers/scsi/scsi.c       | 2 +-
>   drivers/scsi/scsi_error.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 88d46fe..c972eab 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -334,7 +334,7 @@ void scsi_put_command(struct scsi_cmnd *cmd)
>   	list_del_init(&cmd->list);
>   	spin_unlock_irqrestore(&cmd->device->list_lock, flags);
>
> -	cancel_delayed_work(&cmd->abort_work);
> +	WARN_ON_ONCE(delayed_work_pending(&cmd->abort_work));
>
>   	__scsi_put_command(cmd->device->host, cmd);
>   }
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index f17aa7a..5232583 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -193,7 +193,7 @@ scsi_abort_command(struct scsi_cmnd *scmd)
>   		SCSI_LOG_ERROR_RECOVERY(3,
>   			scmd_printk(KERN_INFO, scmd,
>   				    "scmd %p previous abort failed\n", scmd));
> -		cancel_delayed_work(&scmd->abort_work);
> +		WARN_ON_ONCE(delayed_work_pending(&scmd->abort_work));
>   		return FAILED;
>   	}
>
>
The first bit is okay, the second isn't.

The second bit is for these cases where the abort got scheduled (in 
scsi_abort_command()), but the workqueue didn't get executed by the 
time the next timeout occured.
I know, highly unlikely, but there is no safeguarding that it 
_cannot_ happen.
So the second cancel_delayed_work() has to stay.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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