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From: James Bottomley on 2 Mar 2010 00:30
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(a)broadcom.com>
> ---
> 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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From: Mike Christie on 12 Mar 2010 17:10
On 03/19/2010 12:31 AM, 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.
>
> Signed-off-by: Hugh Daschbach<hdasch(a)broadcom.com>
> ---
> 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);
> 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;
> 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:

Did you try the patch I linked to the last time you posted about this?

I think there should be a patch which fixes this problem here:
http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=commitdiff;h=6c71dcb28ff9b63b814a0b76a256f5dae08d3e0d;hp=3a5b27bf6f29574d667230c7e76e4b83fe3014e0
I think it got into 2.6.34-rc1.

With that patch mode selects should get set up as writes.

Does it work? If it does then I think we just need the attached cleanup
patch which removes the cmd_flags setting. The patch that got merged
fixed the problem of initializing the request properly, but it forgot to
remove the cmd_flags setting.
From: Hugh Daschbach on 12 Mar 2010 17:30
Mike Christie [mailto:michaelc(a)cs.wisc.edu] writes:

> On 03/19/2010 12:31 AM, Hugh Daschbach wrote:
>> The EMC multipath device handler should not change the I/O direction
>> flags of its trespass command request.

....

> Did you try the patch I linked to the last time you posted about this?

I have not. When I read it, I believed it would fix the issue.

> I think there should be a patch which fixes this problem here:
> http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=commitdiff;h=6c71dcb28ff9b63b814a0b76a256f5dae08d3e0d;hp=3a5b27bf6f29574d667230c7e76e4b83fe3014e0
> I think it got into 2.6.34-rc1.

Then I'll pull it and test it.

> With that patch mode selects should get set up as writes.
>
> Does it work? If it does then I think we just need the attached cleanup
> patch which removes the cmd_flags setting. The patch that got merged
> fixed the problem of initializing the request properly, but it forgot to
> remove the cmd_flags setting.

Agree. I'll test it early next week and confirm.

Thanks,
Hugh
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From: Hugh Daschbach on 18 Mar 2010 22:30
Hugh Daschbach [mailto:hdasch(a)broadcom.com] wrote:
> Mike Christie [mailto:michaelc(a)cs.wisc.edu] writes:

>> On 03/19/2010 12:31 AM, Hugh Daschbach wrote:
>>> The EMC multipath device handler should not change the I/O direction
>>> flags of its trespass command request.

....

>> Did you try the patch I linked to the last time you posted about this?

> I have not. When I read it, I believed it would fix the issue.

>> I think there should be a patch which fixes this problem here:
>> http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=commitdiff;h=6c71dcb28ff9b63b814a0b76a256f5dae08d3e0d;hp=3a5b27bf6f29574d667230c7e76e4b83fe3014e0
>> I think it got into 2.6.34-rc1.

> Then I'll pull it and test it.

>> With that patch mode selects should get set up as writes.
>>
>> Does it work? If it does then I think we just need the attached cleanup
>> patch which removes the cmd_flags setting. The patch that got merged
>> fixed the problem of initializing the request properly, but it forgot to
>> remove the cmd_flags setting.

> Agree. I'll test it early next week and confirm.

I have pulled and tested this patch. It does fix my issue.

Thanks,
Hugh

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