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Date: Wed, 10 Apr 2024 13:43:52 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Vincent Donnefort <vdonnefort@...gle.com>
Cc: mhiramat@...nel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
kernel-team@...roid.com, rdunlap@...radead.org, linux-mm@...ck.org
Subject: Re: [PATCH v20 2/5] ring-buffer: Introducing ring-buffer mapping
functions
On Sat, 6 Apr 2024 18:36:46 +0100
Vincent Donnefort <vdonnefort@...gle.com> wrote:
> +int ring_buffer_map(struct trace_buffer *buffer, int cpu,
> + struct vm_area_struct *vma)
> +{
> + struct ring_buffer_per_cpu *cpu_buffer;
> + unsigned long flags, *subbuf_ids;
> + int err = 0;
> +
> + if (!cpumask_test_cpu(cpu, buffer->cpumask))
> + return -EINVAL;
> +
> + cpu_buffer = buffer->buffers[cpu];
> +
> + mutex_lock(&cpu_buffer->mapping_lock);
> +
> + if (cpu_buffer->mapped) {
> + err = __rb_map_vma(cpu_buffer, vma);
> + if (!err)
> + err = __rb_inc_dec_mapped(cpu_buffer, true);
> + mutex_unlock(&cpu_buffer->mapping_lock);
> + return err;
> + }
> +
> + /* prevent another thread from changing buffer/sub-buffer sizes */
> + mutex_lock(&buffer->mutex);
> +
> + err = rb_alloc_meta_page(cpu_buffer);
> + if (err)
> + goto unlock;
> +
> + /* subbuf_ids include the reader while nr_pages does not */
> + subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
> + if (!subbuf_ids) {
> + rb_free_meta_page(cpu_buffer);
> + err = -ENOMEM;
> + goto unlock;
> + }
> +
> + atomic_inc(&cpu_buffer->resize_disabled);
> +
> + /*
> + * Lock all readers to block any subbuf swap until the subbuf IDs are
> + * assigned.
> + */
> + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> + rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
> + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> +
> + err = __rb_map_vma(cpu_buffer, vma);
> + if (!err) {
> + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> + cpu_buffer->mapped = 1;
> + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> + } else {
> + kfree(cpu_buffer->subbuf_ids);
> + cpu_buffer->subbuf_ids = NULL;
> + rb_free_meta_page(cpu_buffer);
> + }
> +unlock:
Nit: For all labels, please add a space before them. Otherwise, diffs will
show "unlock" as the function and not "ring_buffer_map", making it harder
to find where the change is.
Same for the labels below.
-- Steve
> + mutex_unlock(&buffer->mutex);
> + mutex_unlock(&cpu_buffer->mapping_lock);
> +
> + return err;
> +}
> +
> +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
> +{
> + struct ring_buffer_per_cpu *cpu_buffer;
> + unsigned long flags;
> + int err = 0;
> +
> + if (!cpumask_test_cpu(cpu, buffer->cpumask))
> + return -EINVAL;
> +
> + cpu_buffer = buffer->buffers[cpu];
> +
> + mutex_lock(&cpu_buffer->mapping_lock);
> +
> + if (!cpu_buffer->mapped) {
> + err = -ENODEV;
> + goto out;
> + } else if (cpu_buffer->mapped > 1) {
> + __rb_inc_dec_mapped(cpu_buffer, false);
> + goto out;
> + }
> +
> + mutex_lock(&buffer->mutex);
> + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> +
> + cpu_buffer->mapped = 0;
> +
> + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> +
> + kfree(cpu_buffer->subbuf_ids);
> + cpu_buffer->subbuf_ids = NULL;
> + rb_free_meta_page(cpu_buffer);
> + atomic_dec(&cpu_buffer->resize_disabled);
> +
> + mutex_unlock(&buffer->mutex);
> +out:
> + mutex_unlock(&cpu_buffer->mapping_lock);
> +
> + return err;
> +}
> +
> +int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
> +{
> + struct ring_buffer_per_cpu *cpu_buffer;
> + unsigned long reader_size;
> + unsigned long flags;
> +
> + cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
> + if (IS_ERR(cpu_buffer))
> + return (int)PTR_ERR(cpu_buffer);
> +
> + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> +consume:
> + if (rb_per_cpu_empty(cpu_buffer))
> + goto out;
> +
> + reader_size = rb_page_size(cpu_buffer->reader_page);
> +
> + /*
> + * There are data to be read on the current reader page, we can
> + * return to the caller. But before that, we assume the latter will read
> + * everything. Let's update the kernel reader accordingly.
> + */
> + if (cpu_buffer->reader_page->read < reader_size) {
> + while (cpu_buffer->reader_page->read < reader_size)
> + rb_advance_reader(cpu_buffer);
> + goto out;
> + }
> +
> + if (WARN_ON(!rb_get_reader_page(cpu_buffer)))
> + goto out;
> +
> + goto consume;
> +out:
> + /* Some archs do not have data cache coherency between kernel and user-space */
> + flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page));
> +
> + rb_update_meta_page(cpu_buffer);
> +
> + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> + rb_put_mapped_buffer(cpu_buffer);
> +
> + return 0;
> +}
> +
> /*
> * We only allocate new buffers, never free them if the CPU goes down.
> * If we were to free the buffer, then the user would lose any trace that was in
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