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Date: Wed, 12 Jun 2024 10:12:44 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
<mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Andrew Morton <akpm@...ux-foundation.org>, Vincent Donnefort
<vdonnefort@...gle.com>, Joel Fernandes <joel@...lfernandes.org>, Daniel
Bristot de Oliveira <bristot@...hat.com>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, suleiman@...gle.com, Thomas Gleixner
<tglx@...utronix.de>, Vineeth Pillai <vineeth@...byteword.org>, Youssef
Esmat <youssefesmat@...gle.com>, Beau Belgrave <beaub@...ux.microsoft.com>,
Alexander Graf <graf@...zon.com>, Baoquan He <bhe@...hat.com>, Borislav
Petkov <bp@...en8.de>, "Paul E. McKenney" <paulmck@...nel.org>, David
Howells <dhowells@...hat.com>, Mike Rapoport <rppt@...nel.org>, Dave Hansen
<dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, Guenter
Roeck <linux@...ck-us.net>, Ross Zwisler <zwisler@...gle.com>, Kees Cook
<keescook@...omium.org>
Subject: Re: [PATCH v5 01/13] ring-buffer: Allow mapped field to be set
without mapping
On Tue, 11 Jun 2024 22:16:43 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.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) <rostedt@...dmis.org>
> ---
> kernel/trace/ring_buffer.c | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 28853966aa9a..aa8eb878e0d4 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -491,6 +491,7 @@ struct ring_buffer_per_cpu {
> unsigned long pages_removed;
>
> unsigned int mapped;
> + unsigned int user_mapped; /* first user space mapping */
This actually needs to be a counter and not just save the mapped value
when it first gets set :-p
As the mappings could technically be incremented and decremented
differently.
I'll send a new patch. But since my long test keeps failing for subtle
things, I'm not going to post another series until the full test passes.
-- Steve
> struct mutex mapping_lock;
> unsigned long *subbuf_ids; /* ID to subbuf VA */
> struct trace_buffer_meta *meta_page;
> @@ -5224,6 +5225,9 @@ 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 +6171,7 @@ 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);
> }
> @@ -6194,7 +6198,7 @@ static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
> if (inc && cpu_buffer->mapped == UINT_MAX)
> return -EBUSY;
>
> - if (WARN_ON(!inc && cpu_buffer->mapped == 0))
> + if (WARN_ON(!inc && cpu_buffer->mapped < cpu_buffer->user_mapped))
> return -EINVAL;
>
> mutex_lock(&cpu_buffer->buffer->mutex);
> @@ -6328,7 +6332,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
>
> mutex_lock(&cpu_buffer->mapping_lock);
>
> - if (cpu_buffer->mapped) {
> + if (cpu_buffer->user_mapped) {
> err = __rb_map_vma(cpu_buffer, vma);
> if (!err)
> err = __rb_inc_dec_mapped(cpu_buffer, true);
> @@ -6359,12 +6363,15 @@ 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);
> +
> 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;
> + /* This is the first time it is mapped externally */
> + cpu_buffer->mapped++;
> + cpu_buffer->user_mapped = cpu_buffer->mapped;
> raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> } else {
> kfree(cpu_buffer->subbuf_ids);
> @@ -6392,10 +6399,10 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
>
> mutex_lock(&cpu_buffer->mapping_lock);
>
> - if (!cpu_buffer->mapped) {
> + if (!cpu_buffer->user_mapped) {
> err = -ENODEV;
> goto out;
> - } else if (cpu_buffer->mapped > 1) {
> + } else if (cpu_buffer->mapped > cpu_buffer->user_mapped) {
> __rb_inc_dec_mapped(cpu_buffer, false);
> goto out;
> }
> @@ -6403,7 +6410,10 @@ 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;
> + /* This is the last user space mapping */
> + if (!WARN_ON_ONCE(cpu_buffer->mapped != cpu_buffer->user_mapped))
> + cpu_buffer->mapped--;
> + cpu_buffer->user_mapped = 0;
>
> raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
>
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