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From: Christian Brauner <[email protected]>
To: Al Viro <[email protected]>
Cc: Jens Axboe <[email protected]>,
	syzbot <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [syzbot] WARNING in mntput_no_expire (2)
Date: Tue, 6 Apr 2021 15:22:05 +0200	[thread overview]
Message-ID: <20210406132205.qnherkzif64xmgxg@wittgenstein> (raw)
In-Reply-To: <YGxeaTzdnxn/[email protected]>

On Tue, Apr 06, 2021 at 01:13:13PM +0000, Al Viro wrote:
> On Tue, Apr 06, 2021 at 02:35:05PM +0200, Christian Brauner wrote:
> 
> > And while we're at it might I bring up the possibility of an additional
> > cleanup of how we currently call path_init().
> > Right now we pass the return value from path_init() directly into e.g.
> > link_path_walk() which as a first thing checks for error. Which feels
> > rather wrong and has always confused me when looking at these codepaths.
> 
> Why?

Why is a another function in charge of checking the return value of an
initialization function. If something like path_init() fails why is the
next caller responsible for rejecting it's return value and then we're
passing that failure value through the whole function with if (!err)
ladders but as I said it's mostly style preferences.

> 
> > I get that it might make sense for reasons unrelated to path_init() that
> > link_path_walk() checks its first argument for error but path_init()
> > should be checked for error right away especially now that we return
> > early when LOOKUP_CACHED is set without LOOKUP_RCU.
> 
> But you are making the _callers_ of path_init() do that, for no good
> reason.

I'm confused why having callers of functions responsible for checking
error values is such an out-of-band concept suddenly. I don't think it's
worth arguing over this though.

> 
> > thing especially in longer functions such as path_lookupat() where it
> > gets convoluted pretty quickly. I think it would be cleaner to have
> > something like [1]. The early exists make the code easier to reason
> > about imho. But I get that that's a style discussion.
> 
> Your variant is a lot more brittle, actually.
> 
> > @@ -2424,33 +2424,49 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
> >         int err;
> > 
> >         s = path_init(nd, flags);
> > -       if (IS_ERR(s))
> > -               return PTR_ERR(s);
> 
> Where has that come from, BTW?  Currently path_lookupat() does no such thing.

Hm? Are you maybe overlooking path_init() which assigns straight into
the variable declaration? Or are you referring to sm else?

static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
{
	const char *s = path_init(nd, flags);
	int err;

	if (unlikely(flags & LOOKUP_DOWN) && !IS_ERR(s)) {
		err = handle_lookup_down(nd);
		if (unlikely(err < 0))
			s = ERR_PTR(err);
	}

	while (!(err = link_path_walk(s, nd)) &&
	       (s = lookup_last(nd)) != NULL)
		;

  reply	other threads:[~2021-04-06 13:22 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
2021-04-01 15:45 ` [syzbot] WARNING in mntput_no_expire (2) Christian Brauner
2021-04-01 16:09   ` Jens Axboe
2021-04-01 17:46     ` Christian Brauner
2021-04-01 17:59       ` Christian Brauner
2021-04-01 19:11         ` Al Viro
2021-04-04  2:34           ` Al Viro
2021-04-04  2:38             ` Al Viro
2021-04-04 11:34             ` Christian Brauner
2021-04-04 15:56               ` Al Viro
2021-04-04 16:40                 ` Christian Brauner
2021-04-04 16:44                   ` Al Viro
2021-04-04 17:05                     ` Christian Brauner
2021-04-04 18:50                       ` Al Viro
2021-04-04 20:17                         ` Al Viro
2021-04-05 11:44                           ` Christian Brauner
2021-04-05 16:18                             ` Al Viro
2021-04-05 17:08                               ` Christian Brauner
2021-04-05 18:23                                 ` Al Viro
2021-04-05 18:28                                   ` Al Viro
2021-04-05 20:07                                     ` Christian Brauner
2021-04-06  1:38                                       ` Al Viro
2021-04-06  2:24                                         ` Al Viro
2021-04-06 12:35                                         ` Christian Brauner
2021-04-06 13:13                                           ` Al Viro
2021-04-06 13:22                                             ` Christian Brauner [this message]
2021-04-06 14:15                                               ` Al Viro
2021-04-06 14:23                                                 ` Al Viro
2021-04-06 15:37                                                   ` Jens Axboe
2021-04-06 14:46                                                 ` Christian Brauner
2021-04-04 16:52                   ` Christian Brauner
2021-04-04 16:55                     ` Christian Brauner

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