diff mbox series

[08/15] tracing: Introduce names for ring buffers

Message ID 20231213000452.88295-9-graf@amazon.com (mailing list archive)
State New, archived
Headers show
Series kexec: Allow preservation of ftrace buffers | expand

Commit Message

Alexander Graf Dec. 13, 2023, 12:04 a.m. UTC
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@amazon.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(-)

Comments

Steven Rostedt Dec. 13, 2023, 12:15 a.m. UTC | #1
On Wed, 13 Dec 2023 00:04:45 +0000
Alexander Graf <graf@amazon.com> wrote:

> 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.
> 

Is there a way to use the trace_array name instead?

The trace_array is the structure that represents each tracing instance. And
it already has a name field. And if you can get the associated ring buffer
from that too.

struct trace_array *tr;

	tr->array_buffer.buffer

	tr->name

When you do: mkdir /sys/kernel/tracing/instance/foo

You create a new trace_array instance where tr->name = "foo" and allocates
the buffer for it as well.

-- Steve
Alexander Graf Dec. 13, 2023, 12:35 a.m. UTC | #2
Hi Steve,

On 13.12.23 01:15, Steven Rostedt wrote:
>
> On Wed, 13 Dec 2023 00:04:45 +0000
> Alexander Graf <graf@amazon.com> wrote:
>
>> 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.
>>
> Is there a way to use the trace_array name instead?
>
> The trace_array is the structure that represents each tracing instance. And
> it already has a name field. And if you can get the associated ring buffer
> from that too.
>
> struct trace_array *tr;
>
>          tr->array_buffer.buffer
>
>          tr->name
>
> When you do: mkdir /sys/kernel/tracing/instance/foo
>
> You create a new trace_array instance where tr->name = "foo" and allocates
> the buffer for it as well.

The name in the ring buffer is pretty much just a copy of the trace 
array name. I use it to reconstruct which buffer we're actually 
referring to inside __ring_buffer_alloc().

I'm all ears for alternative suggestions. I suppose we could pass tr as 
argument to ring_buffer_alloc() instead of the name?


Alex




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Steven Rostedt Dec. 13, 2023, 12:44 a.m. UTC | #3
On Wed, 13 Dec 2023 01:35:16 +0100
Alexander Graf <graf@amazon.com> wrote:

> > The trace_array is the structure that represents each tracing instance. And
> > it already has a name field. And if you can get the associated ring buffer
> > from that too.
> >
> > struct trace_array *tr;
> >
> >          tr->array_buffer.buffer
> >
> >          tr->name
> >
> > When you do: mkdir /sys/kernel/tracing/instance/foo
> >
> > You create a new trace_array instance where tr->name = "foo" and allocates
> > the buffer for it as well.  
> 
> The name in the ring buffer is pretty much just a copy of the trace 
> array name. I use it to reconstruct which buffer we're actually 
> referring to inside __ring_buffer_alloc().

No, I rather not tie the ring buffer to the trace_array.

> 
> I'm all ears for alternative suggestions. I suppose we could pass tr as 
> argument to ring_buffer_alloc() instead of the name?

I'll have to spend some time (that I don't currently have :-( ) on looking
at this more. I really don't like the copying of the name into the ring
buffer allocation, as it may be an unneeded burden to maintain, not to
mention the duplicate field.

-- Steve
kernel test robot Dec. 13, 2023, 11:22 a.m. UTC | #4
Hi Alexander,

kernel test robot noticed the following build errors:

[auto build test ERROR on tip/x86/core]
[also build test ERROR on arm64/for-next/core akpm-mm/mm-everything linus/master v6.7-rc5 next-20231213]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Alexander-Graf/mm-memblock-Add-support-for-scratch-memory/20231213-080941
base:   tip/x86/core
patch link:    https://lore.kernel.org/r/20231213000452.88295-9-graf%40amazon.com
patch subject: [PATCH 08/15] tracing: Introduce names for ring buffers
config: i386-buildonly-randconfig-003-20231213 (https://download.01.org/0day-ci/archive/20231213/202312131922.5dJORQu4-lkp@intel.com/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231213/202312131922.5dJORQu4-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202312131922.5dJORQu4-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/trace/ring_buffer_benchmark.c:435:53: error: too few arguments provided to function-like macro invocation
           buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE);
                                                              ^
   include/linux/ring_buffer.h:96:9: note: macro 'ring_buffer_alloc' defined here
   #define ring_buffer_alloc(name, size, flags)                    \
           ^
>> kernel/trace/ring_buffer_benchmark.c:435:11: error: use of undeclared identifier 'ring_buffer_alloc'; did you mean '__ring_buffer_alloc'?
           buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE);
                    ^~~~~~~~~~~~~~~~~
                    __ring_buffer_alloc
   include/linux/ring_buffer.h:88:1: note: '__ring_buffer_alloc' declared here
   __ring_buffer_alloc(const char *name, unsigned long size, unsigned flags,
   ^
   2 errors generated.
--
>> kernel/trace/ring_buffer.c:6096:65: error: too few arguments provided to function-like macro invocation
           buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
                                                                          ^
   include/linux/ring_buffer.h:96:9: note: macro 'ring_buffer_alloc' defined here
   #define ring_buffer_alloc(name, size, flags)                    \
           ^
>> kernel/trace/ring_buffer.c:6096:11: error: use of undeclared identifier 'ring_buffer_alloc'; did you mean '__ring_buffer_alloc'?
           buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
                    ^~~~~~~~~~~~~~~~~
                    __ring_buffer_alloc
   kernel/trace/ring_buffer.c:1873:19: note: '__ring_buffer_alloc' declared here
   EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
                     ^
   2 errors generated.


vim +435 kernel/trace/ring_buffer_benchmark.c

5092dbc96f3acd Steven Rostedt 2009-05-05  429  
5092dbc96f3acd Steven Rostedt 2009-05-05  430  static int __init ring_buffer_benchmark_init(void)
5092dbc96f3acd Steven Rostedt 2009-05-05  431  {
5092dbc96f3acd Steven Rostedt 2009-05-05  432  	int ret;
5092dbc96f3acd Steven Rostedt 2009-05-05  433  
5092dbc96f3acd Steven Rostedt 2009-05-05  434  	/* make a one meg buffer in overwite mode */
5092dbc96f3acd Steven Rostedt 2009-05-05 @435  	buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE);
5092dbc96f3acd Steven Rostedt 2009-05-05  436  	if (!buffer)
5092dbc96f3acd Steven Rostedt 2009-05-05  437  		return -ENOMEM;
5092dbc96f3acd Steven Rostedt 2009-05-05  438  
5092dbc96f3acd Steven Rostedt 2009-05-05  439  	if (!disable_reader) {
5092dbc96f3acd Steven Rostedt 2009-05-05  440  		consumer = kthread_create(ring_buffer_consumer_thread,
5092dbc96f3acd Steven Rostedt 2009-05-05  441  					  NULL, "rb_consumer");
5092dbc96f3acd Steven Rostedt 2009-05-05  442  		ret = PTR_ERR(consumer);
5092dbc96f3acd Steven Rostedt 2009-05-05  443  		if (IS_ERR(consumer))
5092dbc96f3acd Steven Rostedt 2009-05-05  444  			goto out_fail;
5092dbc96f3acd Steven Rostedt 2009-05-05  445  	}
5092dbc96f3acd Steven Rostedt 2009-05-05  446  
5092dbc96f3acd Steven Rostedt 2009-05-05  447  	producer = kthread_run(ring_buffer_producer_thread,
5092dbc96f3acd Steven Rostedt 2009-05-05  448  			       NULL, "rb_producer");
5092dbc96f3acd Steven Rostedt 2009-05-05  449  	ret = PTR_ERR(producer);
5092dbc96f3acd Steven Rostedt 2009-05-05  450  
5092dbc96f3acd Steven Rostedt 2009-05-05  451  	if (IS_ERR(producer))
5092dbc96f3acd Steven Rostedt 2009-05-05  452  		goto out_kill;
5092dbc96f3acd Steven Rostedt 2009-05-05  453  
98e4833ba3c314 Ingo Molnar    2009-11-23  454  	/*
98e4833ba3c314 Ingo Molnar    2009-11-23  455  	 * Run them as low-prio background tasks by default:
98e4833ba3c314 Ingo Molnar    2009-11-23  456  	 */
7ac07434048001 Steven Rostedt 2009-11-25  457  	if (!disable_reader) {
4fd5750af02ab7 Peter Zijlstra 2020-07-20  458  		if (consumer_fifo >= 2)
4fd5750af02ab7 Peter Zijlstra 2020-07-20  459  			sched_set_fifo(consumer);
4fd5750af02ab7 Peter Zijlstra 2020-07-20  460  		else if (consumer_fifo == 1)
4fd5750af02ab7 Peter Zijlstra 2020-07-20  461  			sched_set_fifo_low(consumer);
4fd5750af02ab7 Peter Zijlstra 2020-07-20  462  		else
7ac07434048001 Steven Rostedt 2009-11-25  463  			set_user_nice(consumer, consumer_nice);
7ac07434048001 Steven Rostedt 2009-11-25  464  	}
7ac07434048001 Steven Rostedt 2009-11-25  465  
4fd5750af02ab7 Peter Zijlstra 2020-07-20  466  	if (producer_fifo >= 2)
4fd5750af02ab7 Peter Zijlstra 2020-07-20  467  		sched_set_fifo(producer);
4fd5750af02ab7 Peter Zijlstra 2020-07-20  468  	else if (producer_fifo == 1)
4fd5750af02ab7 Peter Zijlstra 2020-07-20  469  		sched_set_fifo_low(producer);
4fd5750af02ab7 Peter Zijlstra 2020-07-20  470  	else
7ac07434048001 Steven Rostedt 2009-11-25  471  		set_user_nice(producer, producer_nice);
98e4833ba3c314 Ingo Molnar    2009-11-23  472  
5092dbc96f3acd Steven Rostedt 2009-05-05  473  	return 0;
5092dbc96f3acd Steven Rostedt 2009-05-05  474  
5092dbc96f3acd Steven Rostedt 2009-05-05  475   out_kill:
5092dbc96f3acd Steven Rostedt 2009-05-05  476  	if (consumer)
5092dbc96f3acd Steven Rostedt 2009-05-05  477  		kthread_stop(consumer);
5092dbc96f3acd Steven Rostedt 2009-05-05  478  
5092dbc96f3acd Steven Rostedt 2009-05-05  479   out_fail:
5092dbc96f3acd Steven Rostedt 2009-05-05  480  	ring_buffer_free(buffer);
5092dbc96f3acd Steven Rostedt 2009-05-05  481  	return ret;
5092dbc96f3acd Steven Rostedt 2009-05-05  482  }
5092dbc96f3acd Steven Rostedt 2009-05-05  483
diff mbox series

Patch

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;