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？

static int spinand_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(unsigned int, 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：

1. 遍历读取每一个page
2. 如果读出错则直接返回
3. 如果出现坏块，则置位ecc_failed，在函数最后会检查此标志
4. 如果出现位翻转，则暂存最大位翻转的bit位数量
5. 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 @@ static int 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(unsigned int, 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 do this 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

1. 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
2. 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：

1. linux提交有规范文档的，抽时间撸一遍，并翻译发博客
2. 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