Re: [PATCH] mtd/ubi: fix initialization order of ubi subsystems

[Mikhail Kshevetskiy <mikhail.kshevetskiy@gmail.com>]

On Fri, 21 Jun 2019 19:26:37 +0200
Richard Weinberger <richard.weinberger@gmail.com> wrote:

> On Thu, Jun 20, 2019 at 3:28 PM Mikhail Kshevetskiy
> <mikhail.kshevetskiy@gmail.com> wrote:
> >
> > during ubi initialization we have a following calling sequence
> >
> > 1) ubi_attach()
> >
> >    ----------------------------------------------------------------
> >    err = ubi_wl_init(ubi, ai);
> >    if (err) goto out_vtbl;
> >
> >    err = ubi_eba_init(ubi, ai);
> >    if (err) goto out_wl;
> >    ----------------------------------------------------------------
> >
> >    As we can see "eba" subsytem is NOT initialized at the moment of
> >    initializing of "wl" subsystem
> >
> > 2) ubi_wl_init()
> >
> >    it call ensure_wear_leveling() at some moment
> >
> > 3) ensure_wear_leveling()
> >
> >    ---------------------------------------------------------------
> >    e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, u.rb);
> >    e2 = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
> >    if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD)) goto out_unlock;
> >    dbg_wl("schedule wear-leveling");
> >    ---------------------------------------------------------------
> >
> >    so, if no wear-leveling is scheduled than everything is OK
> >
> >    and a little bit below
> >
> >    ---------------------------------------------------------------
> >    wrk->anchor = 0;
> >    wrk->func = &wear_leveling_worker;
> >    if (nested) __schedule_ubi_work(ubi, wrk);
> >    else schedule_ubi_work(ubi, wrk);
> >    ---------------------------------------------------------------
> >
> >    as result we enter to wear_leveling_worker() function
> 
> Well, we schedule work, but don't execute it since the ubi-thread
> is still disabled.
> 
> Can you please share a little more about the problem you are facing?
> Also produce_free_peb() should not get called at this point.
> So before we flip the order of initialization I'd like to understand the
> problem better.

We faced a cycle rebooting in u-boot during ubi initialization. The problem
appears approximately once per week on a random router from our test farm.
We never trigger this problem in linux (only in u-boot).

From the other side ubi code in u-boot is almost the same as ubi code in linux
kernel (it backported from linux periodically), so it make sense to fix it in
linux as well to help with future porting.

PS we send the same patch to u-boot.

Mikhail

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