[PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Jason Yan]

This is an effort to eliminate the uninitialized_var() macro[1].

The use of this macro is the wrong solution because it forces off ANY
analysis by the compiler for a given variable. It even masks "unused
variable" warnings.

Quoted from Linus[2]:

"It's a horrible thing to use, in that it adds extra cruft to the
source code, and then shuts up a compiler warning (even the _reliable_
warnings from gcc)."

The gcc option "-Wmaybe-uninitialized" has been disabled and this change
will not produce any warnnings even with "make W=1".

[1] https://github.com/KSPP/linux/issues/81
[2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
---
 fs/f2fs/data.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 326c63879ddc..e6ec61274d76 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 	};
 #endif
 	int nr_pages;
-	pgoff_t uninitialized_var(writeback_index);
+	pgoff_t writeback_index;
 	pgoff_t index;
 	pgoff_t end;		/* Inclusive */
 	pgoff_t done_index;
-- 
2.25.4

Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Chao Yu]

On 2020/6/15 12:02, Jason Yan wrote:
> This is an effort to eliminate the uninitialized_var() macro[1].
> 
> The use of this macro is the wrong solution because it forces off ANY
> analysis by the compiler for a given variable. It even masks "unused
> variable" warnings.
> 
> Quoted from Linus[2]:
> 
> "It's a horrible thing to use, in that it adds extra cruft to the
> source code, and then shuts up a compiler warning (even the _reliable_
> warnings from gcc)."
> 
> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
> will not produce any warnnings even with "make W=1".
> 
> [1] https://github.com/KSPP/linux/issues/81
> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> 
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Jason Yan <yanaijie@huawei.com>
> ---
>  fs/f2fs/data.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 326c63879ddc..e6ec61274d76 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>  	};
>  #endif
>  	int nr_pages;
> -	pgoff_t uninitialized_var(writeback_index);
> +	pgoff_t writeback_index;

I suggest to delete this variable directly, as we did for mm in
commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).

Thanks,

>  	pgoff_t index;
>  	pgoff_t end;		/* Inclusive */
>  	pgoff_t done_index;
> 

Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Jason Yan]

在 2020/6/15 16:26, Chao Yu 写道:
> On 2020/6/15 12:02, Jason Yan wrote:
>> This is an effort to eliminate the uninitialized_var() macro[1].
>>
>> The use of this macro is the wrong solution because it forces off ANY
>> analysis by the compiler for a given variable. It even masks "unused
>> variable" warnings.
>>
>> Quoted from Linus[2]:
>>
>> "It's a horrible thing to use, in that it adds extra cruft to the
>> source code, and then shuts up a compiler warning (even the _reliable_
>> warnings from gcc)."
>>
>> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
>> will not produce any warnnings even with "make W=1".
>>
>> [1] https://github.com/KSPP/linux/issues/81
>> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>>
>> Cc: Kees Cook <keescook@chromium.org>
>> Signed-off-by: Jason Yan <yanaijie@huawei.com>
>> ---
>>   fs/f2fs/data.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 326c63879ddc..e6ec61274d76 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>>   	};
>>   #endif
>>   	int nr_pages;
>> -	pgoff_t uninitialized_var(writeback_index);
>> +	pgoff_t writeback_index;
> 
> I suggest to delete this variable directly, as we did for mm in
> commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).
> 

Good suggestion, I will send v2.

Thanks,
Jason

> Thanks,
> 
>>   	pgoff_t index;
>>   	pgoff_t end;		/* Inclusive */
>>   	pgoff_t done_index;
>>
> 
> .
> 

Re: [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Kees Cook]

On Mon, Jun 15, 2020 at 04:51:32PM +0800, Jason Yan wrote:
> This is an effort to eliminate the uninitialized_var() macro[1].
> 
> The use of this macro is the wrong solution because it forces off ANY
> analysis by the compiler for a given variable. It even masks "unused
> variable" warnings.
> 
> Quoted from Linus[2]:
> 
> "It's a horrible thing to use, in that it adds extra cruft to the
> source code, and then shuts up a compiler warning (even the _reliable_
> warnings from gcc)."
> 
> Fix it by remove this variable since it is not needed at all.
> 
> [1] https://github.com/KSPP/linux/issues/81
> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> 
> Cc: Kees Cook <keescook@chromium.org>
> Suggested-by: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Jason Yan <yanaijie@huawei.com>
> ---
>  v2: Directly remove this variable.

Thanks! I've applied this to my uninitialized_var() macro removal
series.

-- 
Kees Cook

Re: [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Chao Yu]

On 2020/6/15 16:51, Jason Yan wrote:
> This is an effort to eliminate the uninitialized_var() macro[1].
> 
> The use of this macro is the wrong solution because it forces off ANY
> analysis by the compiler for a given variable. It even masks "unused
> variable" warnings.
> 
> Quoted from Linus[2]:
> 
> "It's a horrible thing to use, in that it adds extra cruft to the
> source code, and then shuts up a compiler warning (even the _reliable_
> warnings from gcc)."
> 
> Fix it by remove this variable since it is not needed at all.
> 
> [1] https://github.com/KSPP/linux/issues/81
> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> 
> Cc: Kees Cook <keescook@chromium.org>
> Suggested-by: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Jason Yan <yanaijie@huawei.com>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,

[PATCH] f2fs: Eliminate usage of uninitialized_var() macro

[Jason Yan]

This is an effort to eliminate the uninitialized_var() macro[1].

The use of this macro is the wrong solution because it forces off ANY
analysis by the compiler for a given variable. It even masks "unused
variable" warnings.

Quoted from Linus[2]:

"It's a horrible thing to use, in that it adds extra cruft to the
source code, and then shuts up a compiler warning (even the _reliable_
warnings from gcc)."

Fix it by remove this variable since it is not needed at all.

[1] https://github.com/KSPP/linux/issues/81
[2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Cc: Kees Cook <keescook@chromium.org>
Suggested-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
---
 v2: Directly remove this variable.

 fs/f2fs/data.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 326c63879ddc..3753ba06531b 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2856,7 +2856,6 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 	};
 #endif
 	int nr_pages;
-	pgoff_t uninitialized_var(writeback_index);
 	pgoff_t index;
 	pgoff_t end;		/* Inclusive */
 	pgoff_t done_index;
@@ -2875,8 +2874,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 		clear_inode_flag(mapping->host, FI_HOT_DATA);
 
 	if (wbc->range_cyclic) {
-		writeback_index = mapping->writeback_index; /* prev offset */
-		index = writeback_index;
+		index = mapping->writeback_index; /* prev offset */
 		end = -1;
 	} else {
 		index = wbc->range_start >> PAGE_SHIFT;
-- 
2.25.4