linux-kernel - [PATCH 08/15] tracing: Introduce names for ring buffers

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Message-ID: <20231213000452.88295-9-graf@amazon.com>
Date:   Wed, 13 Dec 2023 00:04:45 +0000
From:   Alexander Graf <graf@...zon.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <linux-trace-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kexec@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, Eric Biederman <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        "Tom Lendacky" <thomas.lendacky@....com>,
        Ashish Kalra <ashish.kalra@....com>,
        James Gowans <jgowans@...zon.com>,
        Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
        <arnd@...db.de>, <pbonzini@...hat.com>,
        <madvenka@...ux.microsoft.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Usama Arif <usama.arif@...edance.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH 08/15] tracing: Introduce names for ring buffers

With KHO (Kexec HandOver), we want to preserve trace buffers across
kexec. To carry over their state between kernels, the kernel needs a
common handle for them that exists on both sides. As handle we introduce
names for ring buffers. In a follow-up patch, the kernel can then use
these names to recover buffer contents for specific ring buffers.

Signed-off-by: Alexander Graf <graf@...zon.com>
---
 include/linux/ring_buffer.h | 7 ++++---
 kernel/trace/ring_buffer.c  | 5 ++++-
 kernel/trace/trace.c        | 7 ++++---
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 782e14f62201..f34538f97c75 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -85,17 +85,18 @@ void ring_buffer_discard_commit(struct trace_buffer *buffer,
  * size is in bytes for each per CPU buffer.
  */
 struct trace_buffer *
-__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
+__ring_buffer_alloc(const char *name, unsigned long size, unsigned flags,
+		    struct lock_class_key *key);
 
 /*
  * Because the ring buffer is generic, if other users of the ring buffer get
  * traced by ftrace, it can produce lockdep warnings. We need to keep each
  * ring buffer's lock class separate.
  */
-#define ring_buffer_alloc(size, flags)			\
+#define ring_buffer_alloc(name, size, flags)			\
 ({							\
 	static struct lock_class_key __key;		\
-	__ring_buffer_alloc((size), (flags), &__key);	\
+	__ring_buffer_alloc((name), (size), (flags), &__key);	\
 })
 
 int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full);
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 43cc47d7faaf..eaaf823ddedb 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -557,6 +557,7 @@ struct trace_buffer {
 
 	struct rb_irq_work		irq_work;
 	bool				time_stamp_abs;
+	const char			*name;
 };
 
 struct ring_buffer_iter {
@@ -1801,7 +1802,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
  * when the buffer wraps. If this flag is not set, the buffer will
  * drop data when the tail hits the head.
  */
-struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
+struct trace_buffer *__ring_buffer_alloc(const char *name,
+					unsigned long size, unsigned flags,
 					struct lock_class_key *key)
 {
 	struct trace_buffer *buffer;
@@ -1823,6 +1825,7 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 	buffer->flags = flags;
 	buffer->clock = trace_clock_local;
 	buffer->reader_lock_key = key;
+	buffer->name = name;
 
 	init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
 	init_waitqueue_head(&buffer->irq_work.waiters);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9aebf904ff97..7700ca1be2a5 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9384,7 +9384,8 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
 
 	buf->tr = tr;
 
-	buf->buffer = ring_buffer_alloc(size, rb_flags);
+	buf->buffer = ring_buffer_alloc(tr->name ? tr->name : "global_trace",
+					size, rb_flags);
 	if (!buf->buffer)
 		return -ENOMEM;
 
@@ -9421,7 +9422,7 @@ static int allocate_trace_buffers(struct trace_array *tr, int size)
 		return ret;
 
 #ifdef CONFIG_TRACER_MAX_TRACE
-	ret = allocate_trace_buffer(tr, &tr->max_buffer,
+	ret = allocate_trace_buffer(NULL, &tr->max_buffer,
 				    allocate_snapshot ? size : 1);
 	if (MEM_FAIL(ret, "Failed to allocate trace buffer\n")) {
 		free_trace_buffer(&tr->array_buffer);
@@ -10473,7 +10474,7 @@ __init static int tracer_alloc_buffers(void)
 		goto out_free_cpumask;
 	/* Used for event triggers */
 	ret = -ENOMEM;
-	temp_buffer = ring_buffer_alloc(PAGE_SIZE, RB_FL_OVERWRITE);
+	temp_buffer = ring_buffer_alloc("temp_buffer", PAGE_SIZE, RB_FL_OVERWRITE);
 	if (!temp_buffer)
 		goto out_rm_hp_state;
 
-- 
2.40.1




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