linux-kernel - Re: [PATCH] mtd: core: only increment ecc_stats.badblocks on confirmed good->bad transition

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <732d629c-d1b9-4483-95c3-9a80bd7b2511@huaweicloud.com>
Date: Tue, 2 Sep 2025 17:03:54 +0800
From: Wang Zhaolong <wangzhaolong@...weicloud.com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: richard@....at, vigneshr@...com, linux-mtd@...ts.infradead.org,
 linux-kernel@...r.kernel.org, chengzhihao1@...wei.com, yi.zhang@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH] mtd: core: only increment ecc_stats.badblocks on
 confirmed good->bad transition


Hi Miquèl,


> Hello Wang,
> 
>> @@ -2349,17 +2351,35 @@ int mtd_block_markbad(struct mtd_info *mtd, loff_t ofs)
>>   		return -EROFS;
>>   
>>   	if (mtd->flags & MTD_SLC_ON_MLC_EMULATION)
>>   		ofs = (loff_t)mtd_div_by_eb(ofs, mtd) * master->erasesize;
>>   
>> -	ret = master->_block_markbad(master, mtd_get_master_ofs(mtd, ofs));
>> +	moffs = mtd_get_master_ofs(mtd, ofs);
>> +
>> +	/* Pre-check: remember current state if available. */
>> +	if (master->_block_isbad)
>> +		oldbad = master->_block_isbad(master, moffs);
>> +
>> +	ret = master->_block_markbad(master, moffs);
>>   	if (ret)
>>   		return ret;
>>   
>> -	while (mtd->parent) {
>> -		mtd->ecc_stats.badblocks++;
>> -		mtd = mtd->parent;
>> +	/*
>> +	 * Post-check and bump stats only on a confirmed good->bad transition.
>> +	 * If _block_isbad is not implemented, be conservative and do not bump.
>> +	 */
>> +	if (master->_block_isbad) {
>> +		/* If it was already bad, nothing to do. */
>> +		if (oldbad > 0)
>> +			return 0;
>> +
>> +		if (master->_block_isbad(master, moffs) > 0) {
>> +			while (mtd->parent) {
>> +				mtd->ecc_stats.badblocks++;
>> +				mtd = mtd->parent;
>> +			}
>> +		}
> 
> I don't think you can assume the block was already bad and must not be
> accounted as a new bad block if you cannot verify that. In this case we
> must remain conservative and tell userspace a new block was marked bad,
> I believe.

Thanks for the review and the clear guidance.

My intent was to avoid inflating badblocks by only bumping the counter on a
confirmed good->bad transition. I tried to ground the decision on observable
state (pre/post isbad) rather than return codes, and to avoid assuming success
implies immediate visibility across drivers. That’s why the increment was
tied to verification and skipped when _block_isbad was unavailable.

Your point about being conservative towards userspace is well taken: if we
cannot verify, we should still account the bad block. Skipping the increment
only when we can prove the block was already bad makes the contract clearer
and avoids under-reporting. Keeping the increment outside the if (_block_isbad)
block also results in simpler, more readable code.


> Said otherwise, the { while () badblocks++ } block shall remain outside
> of the if (_block_isbad) condition and remain untouched. Just bail out
> early if you are sure this is not needed.
> 

I’ll send a V2 shortly that:

- Checks old state when _block_isbad exists and bails out early if already bad
- Otherwise calls ->_block_markbad() and increments the counter on success, with
   the increment left outside of the conditional as you suggested

Thanks again for the direction.

Best regards,
Wang Zhaolong