linux-kernel - Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log

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Date:   Wed, 17 May 2023 17:13:17 +0800
From:   Anand Jain <anand.jain@...cle.com>
To:     Qu Wenruo <quwenruo.btrfs@....com>,
        zhangshida <starzhangzsd@...il.com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangshida@...inos.cn, k2ci <kernel-bot@...inos.cn>
Subject: Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode

On 17/5/23 15:46, Qu Wenruo wrote:
> 
> 
> On 2023/5/16 09:34, zhangshida wrote:
>> From: Shida Zhang <zhangshida@...inos.cn>
>>
>> From: Shida Zhang <zhangshida@...inos.cn>
>>
>> This fixes the following warning reported by gcc 10 under x86_64:
> 
> Full gcc version please.
> Especially you need to check if your gcc10 is the latest release.
> 
> If newer gcc (12.2.1) tested without such error, it may very possible to
> be a false alert.
> 
> And in fact it is.
> 

I also noticed that last_range_start is not actually uninitialized.
However, it is acceptable to initialize a variable to silence the
compiler if necessary, right? We have done something similar in the
past.

Thanks, Anand

> @first_dir_index would only be assigned to @last_range_start if
> last_range_end != 0.
> 
> Thus the loop must have to be executed once, and @last_range_start won't
> be zero.
> 
> Please do check your environment (especially your gcc version and
> backports), before sending such trivial patches.
> Under most cases, it helps nobody.
> 
> Thanks,
> Qu
> 
>>
>> ../fs/btrfs/tree-log.c: In function ‘btrfs_log_inode’:
>> ../fs/btrfs/tree-log.c:6211:9: error: ‘last_range_start’ may be used 
>> uninitialized in this function [-Werror=maybe-uninitialized]
>>   6211 |   ret = insert_dir_log_key(trans, log, path, key.objectid,
>>        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>   6212 |       first_dir_index, last_dir_index);
>>        |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> ../fs/btrfs/tree-log.c:6161:6: note: ‘last_range_start’ was declared here
>>   6161 |  u64 last_range_start;
>>        |      ^~~~~~~~~~~~~~~~
>>
>> Reported-by: k2ci <kernel-bot@...inos.cn>
>> Signed-off-by: Shida Zhang <zhangshida@...inos.cn>
>> ---
>>   fs/btrfs/tree-log.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>> index 9b212e8c70cc..d2755d5e338b 100644
>> --- a/fs/btrfs/tree-log.c
>> +++ b/fs/btrfs/tree-log.c
>> @@ -6158,7 +6158,7 @@ static int 
>> log_delayed_deletions_incremental(struct btrfs_trans_handle *trans,
>>   {
>>       struct btrfs_root *log = inode->root->log_root;
>>       const struct btrfs_delayed_item *curr;
>> -    u64 last_range_start;
>> +    u64 last_range_start = 0;
>>       u64 last_range_end = 0;
>>       struct btrfs_key key;
>>