Re: [PATCH] drivers/scsi/sd.c: fix uninitialized variable in handling medium errors

[Mark Lord <lkml@rtr.ca>]

Andrew Morton wrote:
> Mark Lord <lkml@rtr.ca> wrote:
>>> That's if we think -stable needs this fixed.
>> Let's say a bunch of read bio's get coalesced into a single
>> 200+ sector request.  This then fails on one single bad sector
>> out of the 200+.  Without the patch, there is a very good chance
>> that sd.c will simply fail the entire request, all 200+ sectors.
>>
>> With the patch, it will fail the first block, and then retry
>> the remaining blocks.  And repeat this until something works,
>> or until everything has failed one by one.
> 
> Yowch.  I have the feeling that this'll take our EIO-handling time from
> far-too-long to far-too-long*200.

That's how it always used to work (eg. SUSE9 2.6.5+ kernels; Jens?).

>> What I need to have happen when a request is failed due to bad-media,
>> is have it split the request into a sequence of single-block requests
>> that are passed to the LLD one at a time.  The ones with real bad
>> sectors will then be independently failed, and the rest will get done.
>>
>> Much better.  Much more complex.
>>
>> I'm thinking about something like that, just not sure whether to put it
>> (initially) in libata, sd.c, or the block layer.
> 
> block, I suspect.  My DVD trauma was IDE-induced.  Jens is mulling the
> problem - I'd suggest you coordinate with him.

I've been pinging Jens about it for a couple of weeks now; no response.

> It would be a good thing to fix.
> 
> It's moderately hard to test, though.  Easy enough for DVDs and CDs, but
> it's harder to take a marker pen to a hard drive.

I have a bunch of "pre-marked" SATA drives here just for the purpose..

Cheers