[U-Boot] [PATCH] mtd, ubi: set free_count to zero before walking through erase list

Heiko Schocher
2016-04-22T11:53:00Z

Hello Richard,

Am 22.04.2016 um 12:48 schrieb Richard Weinberger:
> Heiko,
>
> Am 22.04.2016 um 12:20 schrieb Heiko Schocher:
>>> Think of places where work is scheduled but the caller blocked
>>> the worker because the work has to be done later.
>>> Fastmap is one of these use cases but AFAIK it won't matter
>>> as no CPU scheduler is involved and will interrupt Fastmap.
>>
>> Can you explain this a little bit?
>
> As I said, when you are in a code region where parallel
> work must not happen as it will, for example, confuse your state
> you block the worker.
> But you are still allowed to schedule new work which will
> executed after you unblock it.
> For the fastmap example I gave it should be fine but I didn't check
> all code paths in UBI for u-boot single thread safety. :-)
>
> What I wanted to say is that executing work directly at schedule
> time does not match 1:1 the POV of Linux UBI and is error prone.
> These are issues you won't notice by compile testing.

Ok, thanks for the explanation!

> An alternative approach would be not executing work
> directly while scheduling it but in produce_free_peb().
> UBI is designed to work with the worker being disabled.
> All UBI work will then happen synchronous and should also work
> in u-boot.

Sounds good!

>>> In the long run I suggest removing the whole Linux UBI implementation
>>> from u-boot and add a small (read only!) implementation which can
>>> also read UBIFS. Reading UBIFS is not a big deal. Also journal reply
>>> can be done in-memory.
>>
>> Hmm.. I think read only is not for all boards an option, as we also
>> create UBI Volumes and/or write to them in U-Boot ...
>
> Depends.
> IMHO a bootloader has exactly one job, loading a kernel
> and booting it. And not being a poor man's general purpose operating
> system where you can also do management stuff like managing UBI volumes. ;-)

Heh...

bye,
Heiko
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