[ENBD] Doubled requests

[Arne Wiebalck]

On Tue, 13 Jan 2004, Peter T. Breuer wrote:

> > it is the same bh, shouldn't it be a different one?
>
> The bh's can be reused, indeed, most likely are, in the normal course
> of events.

Yes, bhs are being reused, but here we have two requests arriving at the
device in a very short period of time. I can't imagine that the bh has
already been released and put back for reuse. I wouldn't wonder if the bh
struct is reused several requests later, but for two adjacent reqs?

>
> I can think of no way the device can generate two consecutive requests
> for the same block.
>
> Can you please also detail the size of the requests and other details
> about them? Umm, what information? Maybe the full struct layout, or as
> much of it as you can easily see.

The size is 1K, since I see "data wholes" of 1K, but I can dump the full
bh struct and post it.

> > some more twins:
> >
> >     Jan 13 17:47:54 e005 kernel: cr: Suspicious block number: 11777 (last
> >     11777) de6748c0 (de6748c0)
>
> Each request should contain many BH's, in general (i.e., many buffers).
> Is there any more information you can get on the contents of the
> request?

Since my device does not deal with reqs, but only uses a make_req_function,
I only see single BHs.

> Not necessarily. That they are not different may well be a function of
> whatever mechanism it is.


One thought was that they are somewhow returned from my devices to the
kernel with an error and then a retry occurs. For the kernel there would
be no reason to allocate a new BH for that.

However,

i)  My device _should_ notify me about an error scenario.

ii) It does not happen without enbd, i.e. if I use the device directly.


I'll do some testing on a UP machine, but I got little hope that it will
solve the issue, since I am currently running only 1 daemon anyway.

We will see, thanks,

  arne





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 Arne Wiebalck                        Kirchhoff Institute for Physics
                                           Technical Computer Science
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