Re: 2.6.24-rc2-mm1

Boaz Harrosh
2007-11-15T18:15:09Z

On Thu, Nov 15 2007 at 19:15 +0200, Matthew Dharm <mdharm-kernel@one-eyed-alien.net> wrote:
> On Wed, Nov 14, 2007 at 10:23:09AM +0100, Gabriel C wrote:
>> Matthew Dharm wrote:
>>> On Wed, Nov 14, 2007 at 06:33:39AM +0100, Gabriel C wrote:
>>>> Matthew Dharm wrote:
>>>>> On Tue, Nov 13, 2007 at 07:49:24PM -0800, Greg KH wrote:
>>>>>> Matt, are these the errors you were worried about with the patch we were
>>>>>> just talking about tha tis in my tree?
>>>>> I can't tell from these logs.
>>>> There is the dmesg with CONFIG_USB_STORAGE_DEBUG :
>>>>
>>>> http://194.231.229.228/dmesg-2.6.24-rc2-mm1
>>> Good news: This isn't the bug Greg was worried about.
>>>
>>> Bad news: Something is seriously strange here. Note the following from the
>>> logs:
>>>
>>> Nov 14 06:07:43 lara [ 41.890614] usb-storage: Bulk Status S 0x53425355 T 0xd R 0 Stat 0x0
>>> Nov 14 06:07:43 lara [ 41.890616] usb-storage: -- unexpectedly short transfer
>>>
>>> Note the 'R' value of zero -- this is the residue value. It indicates a
>>> complete transfer, and that matches the log lines immediately previous
>>> which indicate a 4K transfer which completed properly.
>>>
>>> If residue is zero, then srb->resid should be zero. Take a look in
>>> linux/usb/storage/transport.c in usb_stor_Bulk_transport()
>>>
>>> If srb->resid is zero, then you should NEVER get the "unexpectedly short
>>> transfer" message. Look at usb_stor_invoke_transport() in the same file.
>> That code got replaced recently but I have no idea about it.
>>
>> ( http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=shortlog see the patches from Boaz Harrosh)
>>
>> srb->resid got replaced by scsi_get_resid() it I see that right.
>>
>> I'm CC'ing the author , he will know I think.
>
> The replacement looks, to my eye, to be logically correct. The patch was
> pretty clean.
>
> Then again, I haven't looked at what is "under the hood" of the accessor
> functions. Perhaps there is a side-effect somewhere in there?
>
> Perhaps a quick debugging test -- print the value of scsi_get_resid(srb)
> just after it's initialized to zero at the top of
> usb_stor_invoke_transport(), and then just after the call to
> us->transport().
>

I have found the bug. My bad sorry about that. Patch below
It is because I switched from use of usb_stor_bulk_transfer_sg()
to usb_stor_bulk_transfer_sglist, but forgot the residual handling.

(Please send scsi bugs to scsi list. My lkml mental filters are
much higher, Sorry for not seeing this yesterday)

----
From: Boaz Harrosh <bharrosh@panasas.com>
Date: Thu, 15 Nov 2007 20:07:56 +0200
Subject: [PATCH] Fix bug in last usb accessor patch

>>> Bad news: Something is seriously strange here. Note the following from the
>>> logs:
>>>
>>> Nov 14 06:07:43 lara [ 41.890614] usb-storage: Bulk Status S 0x53425355 T 0xd R 0 Stat 0x0
>>> Nov 14 06:07:43 lara [ 41.890616] usb-storage: -- unexpectedly short transfer
>>>
>>> Note the 'R' value of zero -- this is the residue value. It indicates a
>>> complete transfer, and that matches the log lines immediately previous
>>> which indicate a 4K transfer which completed properly.
>>>
>>> If residue is zero, then srb->resid should be zero. Take a look in
>>> linux/usb/storage/transport.c in usb_stor_Bulk_transport()
>>>
>>> If srb->resid is zero, then you should NEVER get the "unexpectedly short
>>> transfer" message. Look at usb_stor_invoke_transport() in the same file.
>> That code got replaced recently but I have no idea about it.

wrong resid handling fixed

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
---
drivers/usb/storage/transport.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index d3a84a2..d9f4912 100644
--- a/drivers/usb/storage/transport.c
+++ b/drivers/usb/storage/transport.c
@@ -465,11 +465,12 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
int usb_stor_bulk_srb(struct us_data* us, unsigned int pipe,
struct scsi_cmnd* srb)
{
- int resid = scsi_get_resid(srb);
+ unsigned int partial;
int result = usb_stor_bulk_transfer_sglist(us, pipe, scsi_sglist(srb),
scsi_sg_count(srb), scsi_bufflen(srb),
- &resid);
- scsi_set_resid(srb, resid);
+ &partial);
+
+ scsi_set_resid(srb, scsi_bufflen(srb) - partial);
return result;
}

--
1.5.3.1