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

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Message-Id: <20230529041337.36741-1-bo.wu@vivo.com>
Date:   Mon, 29 May 2023 12:13:37 +0800
From:   Wu Bo <bo.wu@...o.com>
To:     chao@...nel.org
Cc:     bo.wu@...o.com, jaegeuk@...nel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, wubo.oduw@...il.com
Subject: Re: [f2fs-dev] [PATCH 1/1] f2fs: fix args passed to trace_f2fs_lookup_end

On Sat, May 27, 2023 at 09:01:41AM +0800, Chao Yu wrote:
> On 2023/5/27 1:21, Jaegeuk Kim wrote:
> > On 05/24, Wu Bo wrote:
> > > The NULL return of 'd_splice_alias' dosen't mean error.
> > > 
> > > Signed-off-by: Wu Bo <bo.wu@...o.com>
> > > ---
> > >   fs/f2fs/namei.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> > > index 77a71276ecb1..e5a3e39ce90c 100644
> > > --- a/fs/f2fs/namei.c
> > > +++ b/fs/f2fs/namei.c
> > > @@ -577,7 +577,7 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
> > >   #endif
> > >   	new = c(inode, dentry);
> > >   	err = PTR_ERR_OR_ZERO(new);
> > > -	trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
> > > +	trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);
> > 
> > Shouldn't give an error pointer to the dentry field.
> > 
> > How about just giving the err?
> > 
> > -       err = PTR_ERR_OR_ZERO(new);
> > -       trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
> > +       trace_f2fs_lookup_end(dir, dentry, ino, PTR_ERR_OR_ZERO(new));
> 
> static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
> {
> 	if (IS_ERR(ptr))
> 		return PTR_ERR(ptr);
> 	else
> 		return 0;
> }
> 
> For below two cases, PTR_ERR_OR_ZERO(new) will return zero:
> a) f2fs_lookup found existed dentry
> b) f2fs_lookup didn't find existed dentry (-ENOENT case)
> 
> So in below commit, I passed -ENOENT to tracepoint for case b), so we can
> distinguish result of f2fs_lookup in tracepoint, actually, -ENOENT is expected
> value when we create a new file/directory.
> 
> Commit 84597b1f9b05 ("f2fs: fix wrong value of tracepoint parameter")
I can see this commit is try to distinguish the dentry not existed case.
But a normal case which dentry is exactly found will also go through
'd_splice_alias', and its return is also NULL. This makes the tracepoint always
print 'err:-2' like the following:
      ls-11676   [004] .... 329281.943118: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Alarms, ino:7093, err:-2
      ls-11676   [004] .... 329281.943145: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Notifications, ino:7094, err:-2
      ls-11676   [004] .... 329281.943172: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Pictures, ino:7095, err:-2
Even these lookup are acctually successful, this is a bit strange.
> 
> > 
> > 
> > >   	return new;
> > >   out_iput:
> > >   	iput(inode);
> > > -- 
> > > 2.35.3
> 
> 
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