On Tue, 11 Jun 2024 15:43:59 -0700
Guenter Roeck <li...@roeck-us.net> wrote:
> On 6/11/24 12:28, Steven Rostedt wrote:
> > From: "Steven Rostedt (Google)" <rost...@goodmis.org>
> >
> > In preparation for having the ring buffer mapped to a dedicated location,
> > which will have the same restrictions as user space memory mapped buffers,
> > allow it to use the "mapped" field of the ring_buffer_per_cpu structure
> > without having the user space meta page mapping.
> >
> > When this starts using the mapped field, it will need to handle adding a
> > user space mapping (and removing it) from a ring buffer that is using a
> > dedicated memory range.
> >
> > Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
> > ---
> > kernel/trace/ring_buffer.c | 11 ++++++++---
> > 1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index 28853966aa9a..78beaccf9c8c 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -5224,6 +5224,9 @@ static void rb_update_meta_page(struct
> > ring_buffer_per_cpu *cpu_buffer)
> > {
> > struct trace_buffer_meta *meta = cpu_buffer->meta_page;
> >
> > + if (!meta)
> > + return;
> > +
> > meta->reader.read = cpu_buffer->reader_page->read;
> > meta->reader.id = cpu_buffer->reader_page->id;
> > meta->reader.lost_events = cpu_buffer->lost_events;
> > @@ -6167,7 +6170,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int
> > cpu)
> >
> > mutex_lock(&cpu_buffer->mapping_lock);
> >
> > - if (!cpu_buffer->mapped) {
> > + if (!cpu_buffer->mapped || !cpu_buffer->meta_page) {
> > mutex_unlock(&cpu_buffer->mapping_lock);
> > return ERR_PTR(-ENODEV);
> > }
> > @@ -6359,12 +6362,13 @@ int ring_buffer_map(struct trace_buffer *buffer,
> > int cpu,
> > */
> > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> > rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
> > +
>
> Picky again. Is that a leftover from something ? I don't see an immediate
> reason
> for the added newline.
Hmm, I could remove it.
>
> > 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;
> > + cpu_buffer->mapped++;
> > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> > } else {
> > kfree(cpu_buffer->subbuf_ids);
> > @@ -6403,7 +6407,8 @@ int ring_buffer_unmap(struct trace_buffer *buffer,
> > int cpu)
> > mutex_lock(&buffer->mutex);
> > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> >
> > - cpu_buffer->mapped = 0;
> > + WARN_ON_ONCE(!cpu_buffer->mapped);
> > + cpu_buffer->mapped--;
>
> This will wrap to UINT_MAX if it was 0. Is that intentional ?
If mapped is non zero, it limits what it can do. If it enters here as zero,
we are really in a unknown state, so yeah, wrapping will just keep it
limited. Which is a good thing.
Do you want me to add a comment there?
-- Steve
>
> >
> > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> >
