Re: UBI leb_write_unlock NULL pointer Oops (continuation)

[Artem Bityutskiy <dedekind1@gmail.com>]

On Mon, 2014-02-03 at 14:56 +0100, Richard Weinberger wrote:
> Am 03.02.2014 13:51, schrieb Wiedemer, Thorsten (Lawo AG):
> > Hi,
> > 
> > I can reproduce it fairly regularly, but not really "quickly". At the moment, I can use a setup of about identical 70 devices.
> > A test over the last weekend resultet In 6 devices showing the bug.
> > What we have are multiple processes which write in different intervals some data on the device and sync it, because this data should be available after a power cut.
> > Perhaps I can force the error more often in writing test processes with shorter write/sync intervals.
> > 
> > If I have further access to the "big" setup for some days, I will try to make a test without preemption.
> 
> Hmm, ok.
> Please also apply this patch, just in case...
> 
> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
> index 0e11671d..48fd2aa 100644
> --- a/drivers/mtd/ubi/eba.c
> +++ b/drivers/mtd/ubi/eba.c
> @@ -301,6 +301,7 @@ static void leb_write_unlock(struct ubi_device *ubi, int vol_id, int lnum)
> 
>  	spin_lock(&ubi->ltree_lock);
>  	le = ltree_lookup(ubi, vol_id, lnum);
> +	ubi_assert(le);
>  	le->users -= 1;
>  	ubi_assert(le->users >= 0);
>  	up_write(&le->mutex);

The UBI LEB locking is a bit over-designed, it could be simplified, may
be this could help looking for the problem.

The this report does really sound like there is something specific to
Thorsten's system which corrupts memory.

And it is difficult to debug this via the mailing list. Thorsten should
start adding various checks like this and try to come closer to the
root-cause.

-- 
Best Regards,
Artem Bityutskiy