linux-kernel - Re: [PATCH v2 1/1] f2fs: fix args passed to trace_f2fs_lookup

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Date:   Wed, 31 May 2023 09:11:54 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Wu Bo <bo.wu@...o.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, wubo.oduw@...il.com
Subject: Re: [PATCH v2 1/1] f2fs: fix args passed to trace_f2fs_lookup_end

On 2023/5/31 7:32, Jaegeuk Kim wrote:
> On 05/30, Wu Bo wrote:
>> The NULL return of 'd_splice_alias' dosen't mean error. Thus the
>> successful case will also return NULL, which makes the tracepoint always
>> print 'err=-ENOENT'.
>>
>> Signed-off-by: Wu Bo <bo.wu@...o.com>
>> ---
>>   fs/f2fs/namei.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>> index 77a71276ecb1..0c5e4c424eab 100644
>> --- a/fs/f2fs/namei.c
>> +++ b/fs/f2fs/namei.c
>> @@ -576,8 +576,9 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
>>   	}
>>   #endif
>>   	new = d_splice_alias(inode, dentry);
>> -	err = PTR_ERR_OR_ZERO(new);
>> -	trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
>> +	if (IS_ERR(new))
>> +		err = PTR_ERR(new);
>> +	trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);
> 
> Again, new can be an error pointer, and the previous err was supposed to be
> zero or -ENOENT.
> 
> case 1) dentry exists: err (0) with new (NULL) --> dentry, err=0
> case 2) dentry exists: err (0) with new (VALID) --> new, err=0
> case 3) dentry exists: err (0) with new (ERR) --> dentry, err=ERR
> case 4) no dentry exists: err (-ENOENT) with new (NULL) --> dentry, err=-ENOENT
> case 4) no dentry exists: err (-ENOENT) with new (VALID) --> new, err=-ENOENT
> case 5) no dentry exists: err (-ENOENT) with new (ERR) --> dentry, err=ERR
> 
> 	trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry,
> 				ino, IS_ERR(new) ? PTR_ERR(new) : err);

Agreed, could you please add above description in commit message?

Thanks,

> 
> 
>>   	return new;
>>   out_iput:
>>   	iput(inode);
>> -- 
>> 2.35.3