Turns out the bidi handling could cause a use after free in this
version, I'll respin it with a fix for that.
On Wed, Feb 26, 2014 at 06:23:21AM -0800, Christoph Hellwig wrote:
> By folding scsi_end_request into its only caller we can significantly clean
> up the completion logic. We can use simple goto labels now to only have
> a single place to finish or requeue command there instead of the previous
> convoluted logic.
>
> Note that the switch from __scsi_release_buffers without the bidi check
> argument to scsi_release_buffers is always correct as we handle bidi
> commands separately in scsi_io_completion and they never reach the path
> scsi_end_request was called from.
>
> Signed-off-by: Christoph Hellwig <h...@lst.de>
> ---
> drivers/scsi/scsi_lib.c | 119
> +++++++++++++----------------------------------
> 1 file changed, 32 insertions(+), 87 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 62ec84b..51063ca 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -540,66 +540,6 @@ void scsi_run_host_queues(struct Scsi_Host *shost)
>
> static void __scsi_release_buffers(struct scsi_cmnd *, int);
>
> -/*
> - * Function: scsi_end_request()
> - *
> - * Purpose: Post-processing of completed commands (usually invoked at end
> - * of upper level post-processing and scsi_io_completion).
> - *
> - * Arguments: cmd - command that is complete.
> - * error - 0 if I/O indicates success, < 0 for I/O error.
> - * bytes - number of bytes of completed I/O
> - * requeue - indicates whether we should requeue leftovers.
> - *
> - * Lock status: Assumed that lock is not held upon entry.
> - *
> - * Returns: cmd if requeue required, NULL otherwise.
> - *
> - * Notes: This is called for block device requests in order to
> - * mark some number of sectors as complete.
> - *
> - * We are guaranteeing that the request queue will be goosed
> - * at some point during this call.
> - * Notes: If cmd was requeued, upon return it will be a stale pointer.
> - */
> -static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int error,
> - int bytes, int requeue)
> -{
> - struct request_queue *q = cmd->device->request_queue;
> - struct request *req = cmd->request;
> -
> - /*
> - * If there are blocks left over at the end, set up the command
> - * to queue the remainder of them.
> - */
> - if (blk_end_request(req, error, bytes)) {
> - /* kill remainder if no retrys */
> - if (error && scsi_noretry_cmd(cmd))
> - blk_end_request_all(req, error);
> - else {
> - if (requeue) {
> - /*
> - * Bleah. Leftovers again. Stick the
> - * leftovers in the front of the
> - * queue, and goose the queue again.
> - */
> - scsi_release_buffers(cmd);
> - scsi_requeue_command(q, cmd);
> - cmd = NULL;
> - }
> - return cmd;
> - }
> - }
> -
> - /*
> - * This will goose the queue request function at the end, so we don't
> - * need to worry about launching another command.
> - */
> - __scsi_release_buffers(cmd, 0);
> - scsi_next_command(cmd);
> - return NULL;
> -}
> -
> static inline unsigned int scsi_sgtable_index(unsigned short nents)
> {
> unsigned int index;
> @@ -751,16 +691,9 @@ static int __scsi_error_from_host_byte(struct scsi_cmnd
> *cmd, int result)
> *
> * Returns: Nothing
> *
> - * Notes: This function is matched in terms of capabilities to
> - * the function that created the scatter-gather list.
> - * In other words, if there are no bounce buffers
> - * (the normal case for most drivers), we don't need
> - * the logic to deal with cleaning up afterwards.
> - *
> - * We must call scsi_end_request(). This will finish off
> - * the specified number of sectors. If we are done, the
> - * command block will be released and the queue function
> - * will be goosed. If we are not done then we have to
> + * Notes: We will finish off the specified number of sectors. If we
> + * are done, the command block will be released and the queue
> + * function will be goosed. If we are not done then we have to
> * figure out what to do next:
> *
> * a) We can call scsi_requeue_command(). The request
> @@ -769,7 +702,7 @@ static int __scsi_error_from_host_byte(struct scsi_cmnd
> *cmd, int result)
> * be used if we made forward progress, or if we want
> * to switch from READ(10) to READ(6) for example.
> *
> - * b) We can call scsi_queue_insert(). The request will
> + * b) We can call __scsi_queue_insert(). The request will
> * be put back on the queue and retried using the same
> * command as before, possibly after a delay.
> *
> @@ -824,12 +757,8 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned
> int good_bytes)
> * both sides at once.
> */
> req->next_rq->resid_len = scsi_in(cmd)->resid;
> -
> - scsi_release_buffers(cmd);
> blk_end_request_all(req, 0);
> -
> - scsi_next_command(cmd);
> - return;
> + goto next_command;
> }
> }
>
> @@ -865,12 +794,25 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned
> int good_bytes)
> }
>
> /*
> - * A number of bytes were successfully read. If there
> - * are leftovers and there is some kind of error
> - * (result != 0), retry the rest.
> + * If we finished all bytes in the request we are done now.
> */
> - if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
> - return;
> + if (!blk_end_request(req, error, good_bytes))
> + goto next_command;
> +
> + /*
> + * Kill remainder if no retrys.
> + */
> + if (error && scsi_noretry_cmd(cmd)) {
> + blk_end_request_all(req, error);
> + goto next_command;
> + }
> +
> + /*
> + * If there had been no error, but we have leftover bytes in the
> + * requeues just queue the command up again.
> + */
> + if (result == 0)
> + goto requeue;
>
> error = __scsi_error_from_host_byte(cmd, result);
>
> @@ -992,7 +934,6 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned
> int good_bytes)
> switch (action) {
> case ACTION_FAIL:
> /* Give up and fail the remainder of the request */
> - scsi_release_buffers(cmd);
> if (!(req->cmd_flags & REQ_QUIET)) {
> if (description)
> scmd_printk(KERN_INFO, cmd, "%s\n",
> @@ -1002,12 +943,11 @@ void scsi_io_completion(struct scsi_cmnd *cmd,
> unsigned int good_bytes)
> scsi_print_sense("", cmd);
> scsi_print_command(cmd);
> }
> - if (blk_end_request_err(req, error))
> - scsi_requeue_command(q, cmd);
> - else
> - scsi_next_command(cmd);
> - break;
> + if (!blk_end_request_err(req, error))
> + goto next_command;
> + /*FALLTHRU*/
> case ACTION_REPREP:
> + requeue:
> /* Unprep the request and put it back at the head of the queue.
> * A new command will be prepared and issued.
> */
> @@ -1023,6 +963,11 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned
> int good_bytes)
> __scsi_queue_insert(cmd, SCSI_MLQUEUE_DEVICE_BUSY, 0);
> break;
> }
> + return;
> +
> +next_command:
> + scsi_release_buffers(cmd);
> + scsi_next_command(cmd);
> }
>
> static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer
> *sdb,
> --
> 1.7.10.4
>
> --
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