Re: [PATCH] tracing: Add persistent ring buffer selftest

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi Steve,

Here is a patch to add a selftest for the persistent ring buffer.
I think we can extend this to add more test pattern, but maybe
we can test one pattern at once.

Thank you,

On Tue, 10 Mar 2026 19:16:13 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Add a self-destractive test for the persistent ring buffer. This
> will invalidate some sub-buffer pages in the persistent ring buffer
> when kernel gets panic, and check whether the number of detected
> invalid pages is the same as record after reboot.
> 
> This can ensure the kernel correctly recover partially corrupted
> persistent ring buffer when boot.
> 
> The test only runs on the persistent ring buffer whose name is
> "ptracingtest". And user has to fill it up with events before
> kernel panics.
> 
> To run the test, enable CONFIG_RING_BUFFER_PERSISTENT_SELFTEST
> and you have to setup the kernel cmdline;
> 
>  reserve_mem=20M:2M:trace trace_instance=ptracingtest^traceoff@trace
>  panic=1
> 
> And run following commands after the 1st boot;
> 
>  cd /sys/kernel/tracing/instances/ptracingtest
>  echo 1 > tracing_on
>  echo 1 > events/enable
>  sleep 3
>  echo c > /proc/sysrq-trigger
> 
> After panic message, the kernel will reboot and run the verification
> on the persistent ring buffer, e.g.
> 
>  Ring buffer meta [1] invalid buffer page detected
>  Ring buffer meta [1] is from previous boot! (318 pages discarded)
>  Ring buffer testing [1]: PASSED (318/318)
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  include/linux/ring_buffer.h |    1 +
>  kernel/trace/Kconfig        |   15 +++++++++++++
>  kernel/trace/ring_buffer.c  |   51 +++++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace.c        |    4 +++
>  4 files changed, 71 insertions(+)
> 
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index 876358cfe1b1..927b6e8587cb 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -238,6 +238,7 @@ int ring_buffer_subbuf_size_get(struct trace_buffer *buffer);
>  
>  enum ring_buffer_flags {
>  	RB_FL_OVERWRITE		= 1 << 0,
> +	RB_FL_TESTING		= 1 << 1,
>  };
>  
>  #ifdef CONFIG_RING_BUFFER
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 49de13cae428..2e6f3b7c6a31 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -1202,6 +1202,21 @@ config RING_BUFFER_VALIDATE_TIME_DELTAS
>  	  Only say Y if you understand what this does, and you
>  	  still want it enabled. Otherwise say N
>  
> +config RING_BUFFER_PERSISTENT_SELFTEST
> +	bool "Enable persistent ring buffer selftest"
> +	depends on RING_BUFFER
> +	help
> +	  Run a selftest on the persistent ring buffer which names
> +	  "ptracingtest" (and its backup) when panic_on_reboot by
> +	  invalidating ring buffer pages.
> +	  Note that user has to enable events on the persistent ring
> +	  buffer manually to fill up ring buffers before rebooting.
> +	  Since this invalidates the data on test target ring buffer,
> +	  "ptracingtest" persistent ring buffer must not be used for
> +	  actual tracing, but only for testing.
> +
> +	  If unsure, say N
> +
>  config MMIOTRACE_TEST
>  	tristate "Test module for mmiotrace"
>  	depends on MMIOTRACE && m
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index a86a036b4100..44268751a02c 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -63,6 +63,7 @@ struct ring_buffer_cpu_meta {
>  	unsigned long	commit_buffer;
>  	__u32		subbuf_size;
>  	__u32		nr_subbufs;
> +	__u32		nr_invalid;
>  	int		buffers[];
>  };
>  
> @@ -2086,6 +2087,11 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
>  
>  	pr_info("Ring buffer meta [%d] is from previous boot! (%d pages discarded)\n",
>  		cpu_buffer->cpu, discarded);
> +	if (meta->nr_invalid)
> +		pr_info("Ring buffer testing [%d]: %s (%d/%d)\n",
> +			cpu_buffer->cpu,
> +			(discarded == meta->nr_invalid) ? "PASSED" : "FAILED",
> +			discarded, meta->nr_invalid);
>  	return;
>  
>   invalid:
> @@ -2488,12 +2494,57 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
>  	kfree(cpu_buffer);
>  }
>  
> +#ifdef CONFIG_RING_BUFFER_PERSISTENT_SELFTEST
> +static void rb_test_inject_invalid_pages(struct trace_buffer *buffer)
> +{
> +	struct ring_buffer_per_cpu *cpu_buffer;
> +	struct ring_buffer_cpu_meta *meta;
> +	struct buffer_data_page *dpage;
> +	unsigned long ptr;
> +	int subbuf_size;
> +	int invalid = 0;
> +	int cpu;
> +	int i;
> +
> +	if (!(buffer->flags & RB_FL_TESTING))
> +		return;
> +
> +	guard(preempt)();
> +	cpu = smp_processor_id();
> +
> +	cpu_buffer = buffer->buffers[cpu];
> +	meta = cpu_buffer->ring_meta;
> +	ptr = (unsigned long)rb_subbufs_from_meta(meta);
> +	subbuf_size = meta->subbuf_size;
> +
> +	/* Invalidate even pages. */
> +	for (i = 0; i < meta->nr_subbufs; i += 2) {
> +		int idx = meta->buffers[i];
> +
> +		dpage = (void *)(ptr + idx * subbuf_size);
> +		/* Skip reader page and unused pages */
> +		if (dpage == cpu_buffer->reader_page->page)
> +			continue;
> +		if (!local_read(&dpage->commit))
> +			continue;
> +		local_add(subbuf_size + 1, &dpage->commit);
> +		invalid++;
> +	}
> +
> +	pr_info("Inject invalidated %d pages on CPU%d\n", invalid, cpu);
> +	meta->nr_invalid = invalid;
> +}
> +#else /* !CONFIG_RING_BUFFER_PERSISTENT_SELFTEST */
> +#define rb_test_inject_invalid_pages(buffer)	do { } while (0)
> +#endif
> +
>  /* Stop recording on a persistent buffer and flush cache if needed. */
>  static int rb_flush_buffer_cb(struct notifier_block *nb, unsigned long event, void *data)
>  {
>  	struct trace_buffer *buffer = container_of(nb, struct trace_buffer, flush_nb);
>  
>  	ring_buffer_record_off(buffer);
> +	rb_test_inject_invalid_pages(buffer);
>  	arch_ring_buffer_flush_range(buffer->range_addr_start, buffer->range_addr_end);
>  	return NOTIFY_DONE;
>  }
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 23de3719f495..eccc1ff22f71 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -9336,6 +9336,8 @@ static void setup_trace_scratch(struct trace_array *tr,
>  	memset(tscratch, 0, size);
>  }
>  
> +#define TRACE_TEST_PTRACING_NAME	"ptracingtest"
> +
>  static int
>  allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size)
>  {
> @@ -9348,6 +9350,8 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
>  	buf->tr = tr;
>  
>  	if (tr->range_addr_start && tr->range_addr_size) {
> +		if (!strcmp(tr->name, TRACE_TEST_PTRACING_NAME))
> +			rb_flags |= RB_FL_TESTING;
>  		/* Add scratch buffer to handle 128 modules */
>  		buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0,
>  						      tr->range_addr_start,
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>