첫 커널 패치 제출 시도 1 : 2020.08.02

iamroot16 스터디 진행 중에 발견한 아주 아주 사소한 버그를 경험삼아 커널 패치 제출 과정을 해봄
AustinKim님의 잘 정리된 커널 제출 방법을 그대로 수행
위 글이 있지만 내가 직접 리눅스 커널 패치 제출을 위해 사용한 터미널 명령어 기록을 위해 정리

과정

iamroot16 스터디 진행 중에 버그 발견

percpu 관련 함수인 pcpu_alloc_first_chunk 함수에서 메모리 할당을 위한 사이즈 계산시 아래 부분에 관련한 버그 존재

  // in mm/percpu.c
       /* allocate chunk */
       alloc_size = sizeof(struct pcpu_chunk) +
               BITS_TO_LONGS(region_size >> PAGE_SHIFT);
       chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
  ...
       /* manage populated page bitmap */
       chunk->immutable = true;
       bitmap_fill(chunk->populated, chunk->nr_pages);
  ...
static inline void bitmap_fill(unsigned long *dst, unsigned int nbits)
{
       unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
       memset(dst, 0xff, len);
}

언제 제출해볼 기회가 생길지 몰라서 커널 패치 제출 방법에 대해 자세히 알아보지 않았는데 갑자기 해보고 싶어져 마음만 급했던 상황

AustinKim님의 글을 참고하였지만 마지막에 구글 2단계 인증으로 인해 마지막 제출 부분에 문제를 겪었음

커널 패치 제출물 준비

 $ git add ./mm/percpu.c
 $ git commit -m 'mm/percpu.c: Modify size of populated bitmap of chunk for memory allocation'
 $ git commit --amend --author="Sunghyun Jin <[email protected]>"
 ...
 Write here a description on your patch
 ...

 Signed-off-by: Sunghyun Jin <[email protected]>

 $ git log -p
 $ git format-patch -1
 $ git format-patch -o /tmp/ head^

커널 패치 제출물 컨벤션 검사

 $ ./scripts/checkpatch.pl ./0001-mm-percpu.c-Modify-size-of-populated-bitmap-of-chunk.patch
 total: 0 errors, 0 warnings, 8 lines checked

 ./0001-mm-percpu.c-Modify-size-of-populated-bitmap-of-chunk.patch has no obvious style problems and is ready for submission.

결과

https://marc.info/?l=linux-kernel&m=159637037815556&w=2
https://lkml.org/lkml/2020/8/2/94
급한 마음에 리눅스 커널 패치 컨벤션도 무시해버림
제출한 커밋이 제대로 된건지 피드백 자체가 없어서 모르겠음
- 제출한 패치가 잘못된 수정인지, 제대로 받을 사람에게 보내진건지, 컨벤션 미준수로 스킵 당한건지 …

TODOLIST

커널 컨벤션 확인
커널 패치 제출글 확인
mutt, git send-email 사용법 공부

문제 해결 방법

구글 2단계 인증으로 인한 문제 해결 방법
- (구글 계정 - 보안 - 앱 비밀번호) 설정을 통해 만든 비밀번호 사용

첫 커널 패치 제출 시도 2 : 2020.09.03

SeongJae Park님의 커널 패치 제출에 대한 다른 글link을 참고하여 다시 제출

과정

$ git commit -m 'mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation'
[master 067d96099555] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
 1 file changed, 1 insertion(+), 1 deletion(-)
$ git commit --amend --author="Sunghyun Jin <[email protected]>"
[master 8dc12c30b6e3] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
 Author: Sunghyun Jin <[email protected]>
 Date: Thu Sep 3 20:50:53 2020 +0900
 1 file changed, 1 insertion(+), 1 deletion(-)
$ git log -p
commit 8dc12c30b6e31805e64fe2151464f97741b98e87 (HEAD -> master)
Author: Sunghyun Jin <[email protected]>
Date:   Thu Sep 3 20:50:53 2020 +0900

    mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation

    Variable populated, which is a member of struct pcpu_chunk, is used as a
    unit of size of unsigned long.
    However, size of populated is miscounted. So, I fix this minor part.

    Signed-off-by: Sunghyun Jin <[email protected]>

diff --git a/mm/percpu.c b/mm/percpu.c
index f4709629e6de..1ed1a349eab8 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1316,7 +1316,7 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,

        /* allocate chunk */
        alloc_size = sizeof(struct pcpu_chunk) +
-               BITS_TO_LONGS(region_size >> PAGE_SHIFT);
+               BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);
        chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk)
                panic("%s: Failed to allocate %zu bytes\n", __func__,

$ git log -1
commit 8dc12c30b6e31805e64fe2151464f97741b98e87 (HEAD -> master)
Author: Sunghyun Jin <[email protected]>
Date:   Thu Sep 3 20:50:53 2020 +0900

    mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation

    Variable populated, which is a member of struct pcpu_chunk, is used as a
    unit of size of unsigned long.
    However, size of populated is miscounted. So, I fix this minor part.

    Signed-off-by: Sunghyun Jin <[email protected]>

$ cat ./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
From 8dc12c30b6e31805e64fe2151464f97741b98e87 Mon Sep 17 00:00:00 2001
From: Sunghyun Jin <[email protected]>
Date: Thu, 3 Sep 2020 20:50:53 +0900
Subject: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap
 of chunk for memory allocation

Variable populated, which is a member of struct pcpu_chunk, is used as a
unit of size of unsigned long.
However, size of populated is miscounted. So, I fix this minor part.

Signed-off-by: Sunghyun Jin <[email protected]>
---
 mm/percpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index f4709629e6de..1ed1a349eab8 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1316,7 +1316,7 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,

        /* allocate chunk */
        alloc_size = sizeof(struct pcpu_chunk) +
-               BITS_TO_LONGS(region_size >> PAGE_SHIFT);
+               BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);
        chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
--
2.17.1

$ ./scripts/checkpatch.pl ./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
total: 0 errors, 0 warnings, 8 lines checked

./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch has no obvious style problems and is ready for submission.
$  ./scripts/get_maintainer.pl ./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
Dennis Zhou <[email protected]> (maintainer:PER-CPU MEMORY ALLOCATOR)
Tejun Heo <[email protected]> (maintainer:PER-CPU MEMORY ALLOCATOR)
Christoph Lameter <[email protected]> (maintainer:PER-CPU MEMORY ALLOCATOR)
Andrew Morton <[email protected]> (maintainer:MEMORY MANAGEMENT)
[email protected] (open list:MEMORY MANAGEMENT)
[email protected] (open list)
$ git send-email --to [email protected] ./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
(mbox) Adding cc: Sunghyun Jin <[email protected]> from line 'From: Sunghyun Jin <[email protected]>'
(body) Adding cc: Sunghyun Jin <[email protected]> from line 'Signed-off-by: Sunghyun Jin <[email protected]>'

From: mcsmonk <[email protected]>
To: [email protected]
Cc: Sunghyun Jin <[email protected]>
Subject: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
Date: Thu,  3 Sep 2020 20:53:43 +0900
Message-Id: <[email protected]>
X-Mailer: git-send-email 2.17.1

    The Cc list above has been expanded by additional
    addresses found in the patch commit message. By default
    send-email prompts before sending whenever this occurs.
    This behavior is controlled by the sendemail.confirm
    configuration setting.

    For additional information, run 'git send-email --help'.
    To retain the current behavior, but squelch this message,
    run 'git config --global sendemail.confirm auto'.

Send this email? ([y]es|[n]o|[q]uit|[a]ll): y
OK. Log says:
Server: smtp.googlemail.com
MAIL FROM:<[email protected]>
RCPT TO:<[email protected]>
RCPT TO:<[email protected]>
From: mcsmonk <[email protected]>
To: [email protected]
Cc: Sunghyun Jin <[email protected]>
Subject: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
Date: Thu,  3 Sep 2020 20:53:43 +0900
Message-Id: <[email protected]>
X-Mailer: git-send-email 2.17.1

Result: 250

$ git send-email --to [email protected] ./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
./0001-mm-percpu.c-Modify-calculation-of-size-of-populated-.patch
(mbox) Adding cc: Sunghyun Jin <[email protected]> from line 'From: Sunghyun Jin <[email protected]>'
(body) Adding cc: Sunghyun Jin <[email protected]> from line 'Signed-off-by: Sunghyun Jin <[email protected]>'

From: mcsmonk <[email protected]>
To: [email protected]
Cc: Sunghyun Jin <[email protected]>
Subject: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
Date: Thu,  3 Sep 2020 20:53:43 +0900
Message-Id: <[email protected]>
X-Mailer: git-send-email 2.17.1

    The Cc list above has been expanded by additional
    addresses found in the patch commit message. By default
    send-email prompts before sending whenever this occurs.
    This behavior is controlled by the sendemail.confirm
    configuration setting.

    For additional information, run 'git send-email --help'.
    To retain the current behavior, but squelch this message,
    run 'git config --global sendemail.confirm auto'.

Send this email? ([y]es|[n]o|[q]uit|[a]ll): y
OK. Log says:
Server: smtp.googlemail.com
MAIL FROM:<[email protected]>
RCPT TO:<[email protected]>
RCPT TO:<[email protected]>
From: mcsmonk <[email protected]>
To: [email protected]
Cc: Sunghyun Jin <[email protected]>
Subject: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation
Date: Thu,  3 Sep 2020 20:53:43 +0900
Message-Id: <[email protected]>
X-Mailer: git-send-email 2.17.1

Result: 250

결과

https://lore.kernel.org/linux-mm/[email protected]/T/#u

From: Dennis Zhou <[email protected]>
To: Vlastimil Babka <[email protected]>
Cc: mcsmonk <[email protected]>, [email protected],
	Mike Rapoport <[email protected]>, Dennis Zhou <[email protected]>,
	Tejun Heo <[email protected]>
Subject: Re: [PATCH] mm/percpu.c: Modify calculation of size of populated
 bitmap of chunk for memory allocation
Message-ID: <[email protected]>
References: <[email protected]>
 <[email protected]>
...
List-ID: <linux-mm.kvack.org>
Archived-At: <https://lore.kernel.org/linux-mm/[email protected]/>
List-Archive: <https://lore.kernel.org/linux-mm/>
List-Post: <mailto:[email protected]>

Hello Vlastimil and Sunghyun,

On Thu, Sep 03, 2020 at 03:46:33PM +0200, Vlastimil Babka wrote:
> On 9/3/20 2:41 PM, mcsmonk wrote:
> From: Sunghyun Jin <[email protected]>
> 
> Variable populated, which is a member of struct pcpu_chunk, is used as a
> unit of size of unsigned long.
> However, size of populated is miscounted. So, I fix this minor part.

> +CC folks who touched it last

Thanks for CCing me.

> Nice find! Did you observe e.g. a panic that can be used in the commit log? Or
> were we always lucky thanks to alignment?

Well that is indeed awkward. Luckily the first chunk is a bit special
and only holds 7 dynamic pages. Additionally, the allocation rounds to
SMP_CACHE_BYTES so that would give us 8 bytes to play with as
struct pcpu_chunk is 120 bytes. So, while technically (wrong) the
1 byte was sufficient and the additional buffer is why at least I never
got a panic report to today.

> Is there perhaps a commit that introduced the bug and we can use it as Fixes:?
> My brief look suggests 8ab16c43ea79 ("percpu: change the number of pages marked
> in the first_chunk pop bitmap")

That is the right commit. I'll pick this up and add the fixes line.

> Thanks!

Thanks,
Dennis

> > Signed-off-by: Sunghyun Jin <[email protected]>
> > ---
> >  mm/percpu.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index f4709629e6de..1ed1a349eab8 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -1316,7 +1316,7 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
> >  
> >  	/* allocate chunk */
> >  	alloc_size = sizeof(struct pcpu_chunk) +
> > -		BITS_TO_LONGS(region_size >> PAGE_SHIFT);
> > +		BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);
> >  	chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
> >  	if (!chunk)
> >  		panic("%s: Failed to allocate %zu bytes\n", __func__,

Updated 2020. Sep. 04
- 밤에 커밋하니까 미국 시간 업무 시간대라 빠르게 반응 옴
- 기술적으로 문제 없던 부분이라도 유의미해서인지 잘 반응해줌

최종 결과 2020. Sep. 21

https://github.com/torvalds/linux/commit/b3b33d3c43bbe0177d70653f4e889c78cc37f097

This is a note to let you know that I've just added the patch titled

    percpu: fix first chunk size calculation for populated bitmap

to the 5.8-stable tree which can be found at:
    [http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary](http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary)

The filename of the patch is:
    percpu-fix-first-chunk-size-calculation-for-populated-bitmap.patch
and it can be found in the queue-5.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.


From b3b33d3c43bbe0177d70653f4e889c78cc37f097 Mon Sep 17 00:00:00 2001
From: Sunghyun Jin <[email protected]>
Date: Thu, 3 Sep 2020 21:41:16 +0900
Subject: percpu: fix first chunk size calculation for populated bitmap

From: Sunghyun Jin <[email protected]>

commit b3b33d3c43bbe0177d70653f4e889c78cc37f097 upstream.

Variable populated, which is a member of struct pcpu_chunk, is used as a
unit of size of unsigned long.
However, size of populated is miscounted. So, I fix this minor part.

Fixes: 8ab16c43ea79 ("percpu: change the number of pages marked in the first_chunk pop bitmap")
Cc: <[email protected]> # 4.14+
Signed-off-by: Sunghyun Jin <[email protected]>
Signed-off-by: Dennis Zhou <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

---
mm/percpu.c |    2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1300,7 +1300,7 @@ static struct pcpu_chunk * __init pcpu_a

        /* allocate chunk */
        alloc_size = sizeof(struct pcpu_chunk) +
-               BITS_TO_LONGS(region_size >> PAGE_SHIFT);
+               BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);
        chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk)
                panic("%s: Failed to allocate %zu bytes\n", __func__,


Patches currently in stable-queue which might be from [email protected] are

queue-5.8/percpu-fix-first-chunk-size-calculation-for-populated-bitmap.patch
queue-5.4/percpu-fix-first-chunk-size-calculation-for-populated-bitmap.patch
queue-4.19/percpu-fix-first-chunk-size-calculation-for-populated-bitmap.patch
queue-4.14/percpu-fix-first-chunk-size-calculation-for-populated-bitmap.patch

참고 사이트

Linux Kernel Official Doc
- https://www.kernel.org/doc/html/latest/process/submitting-patches.html
AustinKim님의 커널 제출 방법
- https://kldp.org/node/162104
SeongJae Park님의 커널 제출 방법
- https://dry-kiss.blogspot.com/2012/10/blog-post.html
github 사이트에서 PR시 Linux KernelPRBot의 답장
- https://github.com/ajdlinux/KernelPRBot/blob/master/message.md
KernelNewbies: Outreachyfirstpatch
- https://kernelnewbies.org/Outreachyfirstpatch
git send-email
- https://riptutorial.com/ko/git/example/16977/gmail%EC%97%90%EC%84%9C-git-send-email-%EC%82%AC%EC%9A%A9