linux-kernel - Re: [BUG] 2.6.24-git usb reset problems

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Date:	Tue, 29 Jan 2008 21:28:57 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Alan Stern <stern@...land.harvard.edu>, Greg KH <greg@...ah.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Matthew Dharm <mdharm-usb@...-eyed-alien.net>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [BUG] 2.6.24-git usb reset problems

On Tue, Jan 29 2008 at 21:17 +0200, James Bottomley <James.Bottomley@...senPartnership.com> wrote:
> On Tue, 2008-01-29 at 20:58 +0200, Boaz Harrosh wrote:
>>> Your new code does
>>>
>>> int partial; <- stack uninitialised
>>> sb_stor_bulk_transfer_sglist(..., &partial, ...);
>>> scsi_set_resid(srb, scsi_bufflen(srb) - partial);
>>>
>>> If the function doesn't touch partial, as it doesn't in the error legs,
>>> resid now gets set with rubbish.
>>>
>>> Actually, my code is still wrong .. we have to set it to
>>> scsi_bufflen(srb) - scsi_resid(srb) so that it comes back the same if
>>> left untouched.
>>>
>>>> I have such a device and I get one reset but then every thing works nice.
>>>> This is with debug on. I'll try to make it fail.
>>> James
>>>
>>>
>> Sorry I still don't see it.
>>
>> original code did sb_stor_bulk_transfer_sg(..., &srp->resid, ...)
>>
>> but sb_stor_bulk_transfer_sg does the:
>>  int partial; <- stack uninitialised
>>  sb_stor_bulk_transfer_sglist(..., &partial, ...);
>>
>> and then unconditionally sets *residual = length_left;
>> I do not see an "error legs" case in sb_stor_bulk_transfer_sg().
> 
> This is really programming 101. This:
> 
> static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned
> int pipe,
> 		struct scatterlist *sg, int num_sg, unsigned int length,
> 		unsigned int *act_len)
> {
> 	int result;
> 
> 	/* don't submit s-g requests during abort/disconnect processing */
> 	if (us->flags & ABORTING_OR_DISCONNECTING)
> 		return USB_STOR_XFER_ERROR;
> 
> The return USB_STOR_XFER_ERROR; is called an error leg.  It returns
> without updating *act_len thus leaving &partial uninitialised.
> 
> James
> 
Yes you are right this is a bug, but it is a bug that was there before.
perhaps the stack is just different now then what it used to be.

Jens could you please try that:

diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index d9f4912..b18a5e6 100644
--- a/drivers/usb/storage/transport.c
+++ b/drivers/usb/storage/transport.c
@@ -465,7 +465,7 @@ 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)
 {
-	unsigned int partial;
+	unsigned int partial = 0;
 	int result = usb_stor_bulk_transfer_sglist(us, pipe, scsi_sglist(srb),
 				      scsi_sg_count(srb), scsi_bufflen(srb),
 				      &partial);

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