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来源：广漠飘羽
www.cnblogs.com/gmpy/p/11086762.html
背景
在开发过程中，偶然发现了spinand驱动的一个bug，满怀欣喜地往社区提补丁。这是怎么样的一个bug呢？
staticintspinand_mtd_read(struct mtd_info *mtd, loff_t from,
struct mtd_oob_ops *ops)
{
......
nanddev_io_for_each_page(nand, from, ops, &iter) {
......
ret = spinand_read_page(spinand, &iter.req, enable_ecc);
if (ret < 0 && ret != -EBADMSG) /* 读取数据出错 */
break;
if (ret == -EBADMSG) {
/* -EBADMSG 返回表示坏块 */
ecc_failed = true;
mtd->ecc_stats.failed++;
ret = 0;
} else {
/* 出现位翻转或者读取正常，则记录历史位翻转最大值 */
mtd->ecc_stats.corrected += ret;
max_bitflips = max_t(unsignedint, max_bitflips, ret);
}
ops->retlen += iter.req.datalen;
ops->oobretlen += iter.req.ooblen;
}
if (ecc_failed && !ret)
ret = -EBADMSG;
return ret ? ret : max_bitflips;
}
代码逻辑如下：
遍历读取每一个page
如果读出错则直接返回
如果出现坏块，则置位ecc_failed，在函数最后会检查此标志
如果出现位翻转，则暂存最大位翻转的bit位数量
全部读取完后，如果有置位ecc_failed，则返回坏块错误码；如果出现位翻转，则返回最大位翻转；否则返回0，表示正常
问题出在于，如果刚好最后一次读取出现位翻转，此时ret != 0就直接退出循环，此时会导致坏块标识无效，且返回最后的位翻转量而非历史位翻转最大值。这是代码不严谨的地方。
第一次提交
修改补丁如下，补丁逻辑不再解释。
In function spinand_mtd_read, if the last page to read occurs bitflip,
this function will return error value because veriable ret not equal to 0.
Signed-off-by: liaoweixiong <liaoweixiong@allwinnertech.com>
---
drivers/mtd/nand/spi/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
index 556bfdb..6b9388d 100644
--- a/drivers/mtd/nand/spi/core.c
+++ b/drivers/mtd/nand/spi/core.c
@@ -511,12 +511,12 @@ staticint spinand_mtd_read(struct mtd_info *mtd, loff_t from,
if (ret == -EBADMSG) {
ecc_failed = true;
mtd->ecc_stats.failed++;
- ret = 0;
} else {
mtd->ecc_stats.corrected += ret;
max_bitflips = max_t(unsignedint, max_bitflips, ret);
}
+ ret = 0;
ops->retlen += iter.req.datalen;
ops->oobretlen += iter.req.ooblen;
}
21:13分发出的邮件，21:45分陆续收到两个回复：
<maintainer A>:
Actually, that's exactly what the MTD core expects(see [1]), so you're
the one introducing a regression here.
<maintainer B>:
To me it looks like the patch description is somewhat incorrect, but the
fix itself looks okay, unless I'm getting it wrong.
In case of the last page containing bitflips(ret > 0),
spinand_mtd_read() will return that number of bitflips for the last
page. But to me it looks like it should instead return max_bitflips like
it does when the last page read returns with 0.
以及隔天回复
<maintainer A>:
Oh, you're right. liaoweixiong, can you adjust the commit message
accordingly?
好吧，问题出在与我没把问题描述清楚，改改再提交
第二次提交
只改了comment和补丁标题：
Subject: [PATCH v2] mtd: spinand: read return badly if the last page has bitflips
In case of the last page containing bitflips(ret > 0),
spinand_mtd_read() will return that number of bitflips for the last
page. But to me it looks like it should instead return max_bitflips like
it does when the last page read returns with 0.
然后哗啦啦收到两个Reviewed-by，附带一个建议：
Reviewed-by: <maintainer B>
This should probably be resent with the following tags:
Cc: stable@vger.kernel.org
Fixes: 7529df465248 ("mtd: nand: Add core infrastructure to support SPI
NANDs")
得，再提交一次吧
第三次提交
此时的我提交补丁到社区经验并不多，Maintainer让我resend，我就忐忑开始胡思乱想了：
版本号需要累加么？该怎么标记是重新发送？有两个maintainer已经"认可"了我的补丁（reviewed-by），我改怎么体现到新的邮件中？
仔细想想内容并没改，因此不需要累加版本号；查询前人提交，在邮件标题可以加上RESEND字样；搜索含RESEND字样的前人邮件，刚好找到一个在maintainer reviewed后resend为acked，写在signed-off-by区。
OK，确定下来就重新发吧
Subject: [RESEND PATCH v2] mtd: spinand: read return badly if the last page has bitflips
......
Signed-off-by: liaoweixiong <liaoweixiong@allwinnertech.com>
Acked-by: <maintainer A>
Acked-by: <maintainer B>
Fixes: 7529df465248 ("mtd: nand: Add core infrastructure to support SPI NANDs")
很快，就挨批了...
第四次提交
晚上10点多，收到回复：
<maintainer B>
Why did you change our Reviewed-by tags to Acked-by tags?
额...我也是看别人这么做我才这么做的，大佬生气了！赶紧补救
......
Reviewed-by: <maintainer A>
Reviewed-by: <maintainer B>
Fixes: 7529df465248 ("mtd: nand: Add core infrastructure to support SPI NANDs")
第五次提交
埋下的坑终究是要踩的，很快，再次挨批了
<maintainer C>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to dothis properly.
<maintainer A>
FYI, you should not send the patch to stable@vger.kernel.org, but
instead, as I said in my other reply, add the tag "Cc:
stable@vger.kernel.org". See "Option 1" in the document Greg referred to.
小白赶紧狠补基础操作规范...
第六次提交
......
Reviewed-by: <maintainer A>
Reviewed-by: <maintainer B>
Cc: stable@vger.kernel.org
Fixes: 7529df465248 ("mtd: nand: Add core infrastructure to support SPI NANDs")
总结
哎，我只是挪了一行代码的位置而已啊，Maintainer严审下，我竟然提交了6次！6次！突然感觉心好累。
累归累，问题总结还是需要的
新手不具备提交代码的一些常识，包括 a) 提交中各个tag的含义，在什么时候加这些tag，例如Reviewed-by和Acked-by的差别 b) 提交补丁到stable的注意事项
对补丁的问题描述不够仔细清楚，导致
无法理解，幸好帮我澄清了
解决方法：
linux提交有规范文档的，抽时间撸一遍，并翻译发博客
在发补丁之前，让身边的人帮忙看一下补丁说明是否足够清晰
希望我的经历能帮助到正在或者准备向Linux内核开源社区的小伙伴
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