Re: [f2fs-dev] [PATCH 1/1] f2fs: fix args passed to trace_f2fs_lookup_end

[Chao Yu]

On 2023/5/29 12:13, Wu Bo wrote:
> 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@xxxxxxxx>
> > > > ---
> > > >    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.

Ah, I misunderstand return value's meaning of .lookup.

So, how about this? it only update err if d_splice_alias() returns a negative
value?

if (IS_ERR(new))
	err = PTR_ERR(new);
trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);

Thanks,

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