linux-kernel - Re: [PATCH v6 12/15] ubi: fastmap: Add all fastmap pebs into 'ai->fastmap' when fm->used

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Date:   Tue, 11 Jan 2022 14:56:22 +0100 (CET)
From:   Richard Weinberger <richard@....at>
To:     chengzhihao1 <chengzhihao1@...wei.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        mcoquelin stm32 <mcoquelin.stm32@...il.com>,
        kirill shutemov <kirill.shutemov@...ux.intel.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 12/15] ubi: fastmap: Add all fastmap pebs into
 'ai->fastmap' when fm->used_blocks>=2

----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@...wei.com>
> An: "richard" <richard@....at>
> CC: "Miquel Raynal" <miquel.raynal@...tlin.com>, "Vignesh Raghavendra" <vigneshr@...com>, "mcoquelin stm32"
> <mcoquelin.stm32@...il.com>, "kirill shutemov" <kirill.shutemov@...ux.intel.com>, "Sascha Hauer"
> <s.hauer@...gutronix.de>, "linux-mtd" <linux-mtd@...ts.infradead.org>, "linux-kernel" <linux-kernel@...r.kernel.org>
> Gesendet: Dienstag, 11. Januar 2022 14:23:52
> Betreff: Re: [PATCH v6 12/15] ubi: fastmap: Add all fastmap pebs into 'ai->fastmap' when fm->used_blocks>=2

> 在 2022/1/11 19:57, Richard Weinberger 写道:
>> 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 This can be the most recent but also outdated anchor PEBs.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 Is it exists a case that outdated fastmap PEBs are neither counted into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.

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.

Thanks,
//richard