On Thu, 2010-03-18 at 22:31 -0700, Hugh Daschbach wrote:
> The EMC multipath device handler should not change the I/O direction
> flags of its trespass command request.
>
> The CFQ elevator may BUG if the direction flags on an I/O request are
> changed after allocation. cfq_set_request() and cfq_put_request()
> count READ and WRITE requests separately. Changing the I/O request
> direction after blk_get_request() allocates the request throws off
> this CFQ accounting.
This description doesn't really match what the problem seems to be
below:
> Signed-off-by: Hugh Daschbach <hdasch@xxxxxxxxxxxx>
> ---
> drivers/scsi/device_handler/scsi_dh_emc.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/scsi/device_handler/scsi_dh_emc.c b/drivers/scsi/device_handler/scsi_dh_emc.c
> index 6196675..3709342 100644
> --- a/drivers/scsi/device_handler/scsi_dh_emc.c
> +++ b/drivers/scsi/device_handler/scsi_dh_emc.c
> @@ -269,10 +269,12 @@ static struct request *get_req(struct scsi_device *sdev, int cmd,
> unsigned char *buffer)
> {
> struct request *rq;
> + int mode = READ;
> int len = 0;
>
> - rq = blk_get_request(sdev->request_queue,
> - (cmd == MODE_SELECT) ? WRITE : READ, GFP_NOIO);
> + if (cmd == MODE_SELECT || cmd == MODE_SELECT_10)
> + mode = WRITE;
> + rq = blk_get_request(sdev->request_queue, mode, GFP_NOIO);
So the actual bug is failure to set WRITE for MODE_SELECT_10.
> if (!rq) {
> sdev_printk(KERN_INFO, sdev, "get_req: blk_get_request failed");
> return NULL;
> @@ -284,12 +286,10 @@ static struct request *get_req(struct scsi_device *sdev, int cmd,
> switch (cmd) {
> case MODE_SELECT:
> len = sizeof(short_trespass);
> - rq->cmd_flags |= REQ_RW;
And this is just cosmetic ... the flags already having been set by the
allocation, they don't need to be set again.
> rq->cmd[1] = 0x10;
> break;
> case MODE_SELECT_10:
> len = sizeof(long_trespass);
> - rq->cmd_flags |= REQ_RW;
> rq->cmd[1] = 0x10;
> break;
> case INQUIRY:
Chandra, can you tidy this up and take it, please?
Thanks,
James
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