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SubjectRe: [PATCH v6 12/15] ubi: fastmap: Add all fastmap pebs into 'ai->fastmap' when fm->used_blocks>=2
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>>> ubi_wl_init() is called in both cases, with and without fastmap.
>> I agree.
>>
>>> And ai->fastmap contains all anchor PEBs that scan_fast() found.
>>> This can be the most recent but also outdated anchor PEBs.
>> Is it exists a case that outdated fastmap PEBs are neither counted into
>> 'fmhdr->erase_peb_count' nor scanned into 'ai->fastmap' after attaching
>> by fastmap.
>>
>
> [...]
>
>> I think UBI attaches failed by fastmap if kernel goes here.
>> 1870 err = erase_aeb(ubi, aeb, sync);
>
> Hmm, I think the paranoia check in fastmap.c is too strict these days.
> if (WARN_ON(count_fastmap_pebs(ai) != ubi->peb_count -
> ai->bad_peb_count - fm->used_blocks))
> goto fail_bad;
>
> It does not account ai->fastmap. So if ai->fastmap contains old anchor PEBs
> this check will trigger and force falling back to scanning mode.
> With this check fixed, ubi_wl_init() will erase all old PEBs from ai->fastmap.
Forgive my stubbornness, I think this strict check is good, could you
show me a process to trigger this WARN_ON, it would be nice to provide a
reproducer.
I still insist the point(after my fix patch applied): All outdated
fastmap PEBs are added into 'ai->fastmap'(full scanning case) or counted
into 'fmhdr->erase_peb_count'(fast attached case).
>
> So I agree that this code path is wonky and can be cleaned up. But please be
> extremely careful and give all your changes excessive testing with real workload
> and power-cuts.Let's list all power-cut cases during fastmap updateing(I tried to
simulate some of them on nandsim), in theory, I think the WARN_ON check
is okay and all outdated fastmap PEBs can be erased in next attaching:

ubi_update_fastmap:
1565 for (i = 1; i < new_fm->used_blocks; i++) {
1570 if (!tmp_e) {
1571 if (old_fm && old_fm->e[i]) {
/* sync erase old fm data PEBs */
power-cut!!!
1585 } else {
/* async erase old fm data PEBs */
power-cut!!!
1595 }
1596 } else {
1599 if (old_fm && old_fm->e[i]) {
/* async erase old fm data PEBs */
power-cut!!!
1603 }
1604 }
1605 }
1621 if (old_fm) {
1623 if (!tmp_e) {
/* sync erase old fm anchor PEB */
power-cut!!!
1638 } else {
/* async erase old fm anchor PEB */
power-cut!!!
1644 }
1645 } else {
1658 }
1660 ret = ubi_write_fastmap(ubi, new_fm);

ubi_write_fastmap:
1324 ret = ubi_io_write_vid_hdr(ubi, new_fm->e[0]->pnum, avbuf);
power-cut!!!
1345 for (i = 1; i < new_fm->used_blocks; i++) {
1350 ret = ubi_io_write_vid_hdr(...);
power-cut!!!
1356 }

1358 for (i = 0; i < new_fm->used_blocks; i++) {
1359 ret = ubi_io_write_data(...),
power-cut!!!
1366 }

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