lkml.org 
[lkml]   [2022]   [May]   [5]   [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.
    On Thu, Apr 28, 2022 at 03:54:28PM +1000, Imran Khan wrote:
    > +static struct kernfs_open_node *kernfs_deref_on_raw(struct kernfs_node *kn)
    > +{
    > + return rcu_dereference_raw(kn->attr.open);
    > +}

    Wrapping the above probably isn't helping anything.

    > +/*
    > + * Check ->attr.open corresponding to @kn while holding kernfs_open_file_mutex.
    > + * ->attr.open is modified under kernfs_open_file_mutex. So it can be safely
    > + * accessed outside RCU read-side critical section, while holding the mutex.
    > + */
    > +static struct kernfs_open_node *kernfs_check_on_protected(struct kernfs_node *kn)
    > +{
    > + return rcu_dereference_check(kn->attr.open,
    > + lockdep_is_held(&kernfs_open_file_mutex));
    > +}

    Maybe name this just kernfs_deref_on()?

    > @@ -156,8 +188,9 @@ static void kernfs_seq_stop(struct seq_file *sf, void *v)
    > static int kernfs_seq_show(struct seq_file *sf, void *v)
    > {
    > struct kernfs_open_file *of = sf->private;
    > + struct kernfs_open_node *on = kernfs_deref_on_raw(of->kn);

    I suppose this is protected by the fact that @of is on @on? If so, just add
    the condition to the checked version. The condition doesn't have to be
    perfect - e.g. you can just say that neither @on's and @of's list_head isn't
    empty. While not comprehensive, it'd still provide meaningful protection
    against mistakes and be easier to understand if the deref accessor clearly
    explains the expectations.

    > @@ -201,7 +235,8 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
    > goto out_free;
    > }
    >
    > - of->event = atomic_read(&of->kn->attr.open->event);
    > + on = kernfs_deref_on_raw(of->kn);
    > + of->event = atomic_read(&unrcu_pointer(on)->event);

    Ditto here.

    > @@ -815,7 +843,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
    > __poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
    > {
    > struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry);
    > - struct kernfs_open_node *on = kn->attr.open;
    > + struct kernfs_open_node *on = kernfs_deref_on_raw(kn);

    and here.

    > @@ -922,13 +950,13 @@ void kernfs_notify(struct kernfs_node *kn)
    > return;
    >
    > /* kick poll immediately */
    > - spin_lock_irqsave(&kernfs_open_node_lock, flags);
    > - on = kn->attr.open;
    > + rcu_read_lock();
    > + on = rcu_dereference(kn->attr.open);

    Shouldn't this be kernfs_deref_on() too?

    Thanks.

    --
    tejun

    \
     
     \ /
      Last update: 2022-05-05 22:03    [W:4.093 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site