linux-kernel - Re: [PATCH bpf-next v4 1/5] bpf: Introduce task

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Message-ID: <Zz3CNMZB94Qmy8nY@krava>
Date: Wed, 20 Nov 2024 12:04:20 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Juntong Deng <juntong.deng@...look.com>, ast@...nel.org,
	daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org,
	martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
	yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me,
	haoluo@...gle.com, memxor@...il.com, snorcht@...il.com,
	brauner@...nel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 1/5] bpf: Introduce task_file open-coded
 iterator kfuncs

On Wed, Nov 20, 2024 at 11:55:23AM +0100, Jiri Olsa wrote:
> On Tue, Nov 19, 2024 at 05:53:58PM +0000, Juntong Deng wrote:
> 
> SNIP
> 
> > +/**
> > + * bpf_iter_task_file_next() - Get the next file in bpf_iter_task_file
> > + *
> > + * bpf_iter_task_file_next acquires a reference to the struct file.
> > + *
> > + * The reference to struct file acquired by the previous
> > + * bpf_iter_task_file_next() is released in the next bpf_iter_task_file_next(),
> > + * and the last reference is released in the last bpf_iter_task_file_next()
> > + * that returns NULL.
> > + *
> > + * @it: the bpf_iter_task_file to be checked
> > + *
> > + * @returns a pointer to bpf_iter_task_file_item
> > + */
> > +__bpf_kfunc struct bpf_iter_task_file_item *bpf_iter_task_file_next(struct bpf_iter_task_file *it)
> > +{
> > +	struct bpf_iter_task_file_kern *kit = (void *)it;
> > +	struct bpf_iter_task_file_item *item = &kit->item;
> > +
> > +	if (item->file)
> > +		fput(item->file);
> > +
> 
> missing rcu_read_lock ?

nah user needs to take it explicitly, should have read the whole thing first, sry

jirka

> 
> jirka
> 
> > +	item->file = task_lookup_next_fdget_rcu(item->task, &kit->next_fd);
> > +	item->fd = kit->next_fd;
> > +
> > +	kit->next_fd++;
> > +
> > +	if (!item->file)
> > +		return NULL;
> > +
> > +	return item;
> > +}
> > +
> > +/**
> > + * bpf_iter_task_file_destroy() - Destroy a bpf_iter_task_file
> > + *
> > + * If the iterator does not iterate to the end, then the last
> > + * struct file reference is released at this time.
> > + *
> > + * @it: the bpf_iter_task_file to be destroyed
> > + */
> > +__bpf_kfunc void bpf_iter_task_file_destroy(struct bpf_iter_task_file *it)
> > +{
> > +	struct bpf_iter_task_file_kern *kit = (void *)it;
> > +	struct bpf_iter_task_file_item *item = &kit->item;
> > +
> > +	if (item->file)
> > +		fput(item->file);
> > +}
> > +
> >  __bpf_kfunc_end_defs();
> >  
> >  DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
> > -- 
> > 2.39.5
> >