lkml.org 
[lkml]   [2022]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/5] kernfs: make ->attr.open RCU protected.
Hello,

On Mon, May 16, 2022 at 02:00:50AM +1000, Imran Khan wrote:
> +/*
> + * Deref RCU protected kn->attr.open.
> + * If both @of->list and @kn->attr.open->files are non empty, we can safely
> + * assume that @of is on @kn->attr.open and hence @kn->attr.open will not
> + * vanish and derefeencing is safe here.
> + */

Maybe use proper function comment starting with /**?

> +static struct kernfs_open_node *
> +kernfs_deref_on_check(struct kernfs_open_file *of, struct kernfs_node *kn)
> +{
> + struct kernfs_open_node *on;
> +
> + on = rcu_dereference_check(kn->attr.open, !list_empty(&of->list));
> +
> + if (on && list_empty(&on->files))
> + return NULL;
> + else
> + return on;
> +}

Why does it need to return NULL on empty on->files? We wanna trigger lockdep
warning cuz that's a bug but it's not like the caller can recover from it
(short of causing unexpected user visible error), so I don't see what the
point is.

> If this looks okay then I can replace usage of kernfs_deref_on_raw with
> kernfs_deref_on_check.

So, this is the main deref function without holding the mutex, right? Then
name it kernfs_deref_open_node() (or on but it seem a bit confusing to me).

> > and in the check condition, add the conditions that you need to make this
> > not trigger warning when used in all the places that you wanna use it.
> >
>
> Since ->attr.open is always accessed/modified under kernfs_open_file_mutex, I
> have included this check in helper which should be used only while holding this
> mutex. Do you mean that I should include some additional checks as well in the
> below helper:

Yeah, you're right. _protected makes sense for this one.

Thanks.

--
tejun

\
 
 \ /
  Last update: 2022-05-16 21:36    [W:0.081 / U:0.240 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site