Alan Stern wrote:
quoted text
> On Mon, 27 Oct 2008, Luciano Rocha wrote:
> 
>> On Sat, Oct 25, 2008 at 03:50:07PM -0400, Alan Stern wrote:
>>> On Sat, 25 Oct 2008, Rafael J. Wysocki wrote:
>>>
>>>> [Adding CCs]
>>>>
>>>> On Wednesday, 22 of October 2008, Luciano Rocha wrote:
>>>>> Hello,
>>>>>
>>>>> An external HDD, usb-encased, works fine under 2.6.26.5, but under
>>>>> 2.6.27.2 I get hundreds of errors per second, of 'No Sense [current]'.
>>> You can use usbmon to capture the details of what happens when you plug
>>> in the drive.  Instructions are in the kernel source file
>>> Documentation/usb/usbmon.txt.
>>>
>> Now in 2.6.27.4, same problem. The usb traffic is:
> 
> This looks exactly like the "infinite retry" problem I warned about 
> earlier.  Here are the important parts of the log.  For people who 
> don't know how to interpret these messages, the CDB starts in the 16th 
> byte of the 31-byte messages.  For example, the first command here 
> starts with 0x25 and so it is READ CAPACITY:
> 
>> f21e7cc0 3570408174 S Bo:1:008:1 -115 31 = 55534243 06000000 08000000 80000a25 00000000 00000000 00000000 000000
>> f21e7cc0 3570408264 C Bo:1:008:1 0 31 >
>> f21e72c0 3570408280 S Bi:1:008:2 -115 8 <
>> f21e72c0 3570408389 C Bi:1:008:2 0 8 = 2e9390b0 00000200
>> f21e7cc0 3570408400 S Bi:1:008:2 -115 13 <
>> f21e7cc0 3570408513 C Bi:1:008:2 0 13 = 55534253 06000000 00000000 00
> 
> The response is 0x2e9390b0.  In typical broken fashion, that is 
> undoubtedly the total number of sectors rather than the highest sector 
> number.

Since the READ CAPACITY "off by one" error is so common,
perhaps drivers such as usb-storage could have a hook to
do a pseudo READ CAPACITY. Then if the capacity value
looked odd (in both senses) the driver could do an IO to
the suspect block and if that failed decrement the capacity
value passed back to the mid level.
Put another way, why don't these defective devices trip up
another OS?

BTW a single disk in RAID 0 (seen on a HP E200 controller)
has a shortened capacity value seen in the midlevel on the
corresponding logical drive. That missing chunk is probably
where the RAID controller puts its control information.
Anyway, playing with the capacity value returned by READ
CAPACITY certainly has a precedent.

quoted text
> Later on the system tries to read the contents of what it thinks is the 
> last sector:

I know that happens but it seems strange that upper levels
are reading a block that has never been written to. Read ahead?

Doug Gilbert


quoted text
>> f21e7cc0 3570515635 S Bo:1:008:1 -115 31 = 55534243 0c000000 00020000 80000a28 002e9390 b0000001 00000000 000000
>> f21e7cc0 3570515762 C Bo:1:008:1 0 31 >
>> f21e76c0 3570515776 S Bi:1:008:2 -115 512 <
>> f21e76c0 3570516261 C Bi:1:008:2 -32 0
>> f21e7cc0 3570516281 S Co:1:008:0 s 02 01 0000 0082 0000 0
>> f21e7cc0 3570516387 C Co:1:008:0 0 0
>> f21e7cc0 3570516399 S Bi:1:008:2 -115 13 <
>> f21e7cc0 3570516511 C Bi:1:008:2 0 13 = 55534253 0c000000 00020000 01
> 
> There's no data in the response, and the 01 on the line above 
> indicates Check Condition status.
> 
>> f21e7cc0 3570516524 S Bo:1:008:1 -115 31 = 55534243 0d000000 12000000 80000603 00000012 00000000 00000000 000000
>> f21e7cc0 3570516636 C Bo:1:008:1 0 31 >
>> f21e76c0 3570516649 S Bi:1:008:2 -115 18 <
>> f21e76c0 3570516762 C Bi:1:008:2 0 18 = 70000000 0000000a 00000000 00000000 0000
>> f21e7cc0 3570516779 S Bi:1:008:2 -115 13 <
>> f21e7cc0 3570516886 C Bi:1:008:2 0 13 = 55534253 0d000000 00000000 00
> 
> The automatically-generated REQUEST SENSE gets the 18-byte response you 
> see above.  It is entirely empty (No Sense).
> 
> The remainder of the trace shows the same command being repeated over 
> and over again, with the same result each time.
> 
>> f21e7cc0 3570516936 S Bo:1:008:1 -115 31 = 55534243 0e000000 00020000 80000a28 002e9390 b0000001 00000000 000000
>> f21e7cc0 3570517012 C Bo:1:008:1 0 31 >
>> f21e76c0 3570517031 S Bi:1:008:2 -115 512 <
>> f21e76c0 3570517511 C Bi:1:008:2 -32 0
>> f21e7cc0 3570517533 S Co:1:008:0 s 02 01 0000 0082 0000 0
>> f21e7cc0 3570517637 C Co:1:008:0 0 0
>> f21e7cc0 3570517648 S Bi:1:008:2 -115 13 <
>> f21e7cc0 3570517762 C Bi:1:008:2 0 13 = 55534253 0e000000 00020000 01
>> f21e7cc0 3570517775 S Bo:1:008:1 -115 31 = 55534243 0f000000 12000000 80000603 00000012 00000000 00000000 000000
>> f21e7cc0 3570517886 C Bo:1:008:1 0 31 >
>> f21e76c0 3570517897 S Bi:1:008:2 -115 18 <
>> f21e76c0 3570518011 C Bi:1:008:2 0 18 = 70000000 0000000a 00000000 00000000 0000
>> f21e7cc0 3570518027 S Bi:1:008:2 -115 13 <
>> f21e7cc0 3570518136 C Bi:1:008:2 0 13 = 55534253 0f000000 00000000 00
> etc...
> 
> There's a patch which might help resolve this problem:
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=8bfa24...
> 
> It is already present in 2.6.28-rc1, so it's worth a try.  If it does
> fix things, let me know so I can submit it for a future 2.6.27.stable
> release.
> 
> Alan Stern
> 
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