linux-kernel - [PATCH v5 01/13] ring-buffer: Allow mapped field to be set without mapping

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Date: Tue, 11 Jun 2024 22:16:43 -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: [PATCH v5 01/13] ring-buffer: Allow mapped field to be set without mapping

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 */
 	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);

-- 
2.43.0