Re: [PATCH] Don't change direction flags in struct request.

From: Mike Christie
Date: Tue Mar 02 2010 - 02:52:11 EST

On 03/01/2010 11:26 PM, James Bottomley wrote:
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

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,
+ 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.

I think we have a fix for this and some len issues in that module that was sent here:
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