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

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Date:   Sat, 15 Jan 2022 16:46:07 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Richard Weinberger <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>
Subject: Re: [PATCH v6 12/15] ubi: fastmap: Add all fastmap pebs into
 'ai->fastmap' when fm->used_blocks>=2

>> Yes. But if you look into ubi_wl_init() you see that fastmap anchor PEBs
>> get erases synchronously(!). The comment before the erasure explains why.
> About erasing fastmap anchor PEB synchronously, I admit curreunt UBI 
> implementation cannot satisfy it, even with my fix applied. Wait, it 
> seems that UBI has never made it sure. Old fastmap PEBs could be erased 
> asynchronously, they could be counted into 'fmh->erase_peb_count' even 
> in early UBI implementation code, so old fastmap anchor PEB will be 
> added into 'ai->erase' and be erased asynchronously in next attaching. 
In next attaching old fastmap PEBs will be processed as following:
ubi_attach_fastmap -> add_aeb(ai, &ai->erase...)
ubi_wl_init
   list_for_each_entry_safe(aeb, tmp, &ai->erase)
     erase_aeb       // erase asynchronously
       ubi->lookuptbl[e->pnum] = e
   list_for_each_entry(aeb, &ai->fastmap, u.list)
     e = ubi_find_fm_block(ubi, aeb->pnum)
     if (e) {
        ...
     } else {
       if (ubi->lookuptbl[aeb->pnum])     // old fastmap PEBs are 
assigned to 'ubi->lookuptbl'
         continue;
     }
> But, I feel it is not a problem, find_fm_anchor() can help us find out 
> the right fastmap anchor PEB according seqnum.