[PATCH v15 0/5] ring-buffer: Making persistent ring buffers robust

[PATCH v15 0/5] ring-buffer: Making persistent ring buffers robust

[Masami Hiramatsu (Google)]

Hi,

Here is the 15th version of improvement patches for making persistent
ring buffers robust to failures.
The previous version is here:

https://lore.kernel.org/all/177487498530.3463592.12715592581212799257.stgit@mhiramat.tok.corp.google.com/

This version fixes warning if reader see contiguous multiple
empty (invalidated) pages on the recovered persistent ring buffer
[2/5], do not show discarded pages if it is 0 [2/5], use pr_warn()
for showing test result [4/5], and inject errors to the pages which
is multiples of 5 too[4/5].
This also drops "Reset RB_MISSED_* flags" patch, and add a patch
to show commit number on each data page [5/5] for debugging.

In this version, I added arm64 maitainers to request their
review for [1/5], which introduces asm/ring_buffer.h for flushing
the cache before reboot.

Thank you,

---

Masami Hiramatsu (Google) (5):
      ring-buffer: Flush and stop persistent ring buffer on panic
      ring-buffer: Skip invalid sub-buffers when validating persistent ring buffer
      ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer
      ring-buffer: Add persistent ring buffer invalid-page inject test
      ring-buffer: Show commit numbers in buffer_meta file


 arch/alpha/include/asm/Kbuild        |    1 
 arch/arc/include/asm/Kbuild          |    1 
 arch/arm/include/asm/Kbuild          |    1 
 arch/arm64/include/asm/ring_buffer.h |   10 +
 arch/csky/include/asm/Kbuild         |    1 
 arch/hexagon/include/asm/Kbuild      |    1 
 arch/loongarch/include/asm/Kbuild    |    1 
 arch/m68k/include/asm/Kbuild         |    1 
 arch/microblaze/include/asm/Kbuild   |    1 
 arch/mips/include/asm/Kbuild         |    1 
 arch/nios2/include/asm/Kbuild        |    1 
 arch/openrisc/include/asm/Kbuild     |    1 
 arch/parisc/include/asm/Kbuild       |    1 
 arch/powerpc/include/asm/Kbuild      |    1 
 arch/riscv/include/asm/Kbuild        |    1 
 arch/s390/include/asm/Kbuild         |    1 
 arch/sh/include/asm/Kbuild           |    1 
 arch/sparc/include/asm/Kbuild        |    1 
 arch/um/include/asm/Kbuild           |    1 
 arch/x86/include/asm/Kbuild          |    1 
 arch/xtensa/include/asm/Kbuild       |    1 
 include/asm-generic/ring_buffer.h    |   13 ++
 include/linux/ring_buffer.h          |    1 
 kernel/trace/Kconfig                 |   31 ++++
 kernel/trace/ring_buffer.c           |  258 ++++++++++++++++++++++++++--------
 kernel/trace/trace.c                 |    4 +
 26 files changed, 273 insertions(+), 64 deletions(-)
 create mode 100644 arch/arm64/include/asm/ring_buffer.h
 create mode 100644 include/asm-generic/ring_buffer.h

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

[PATCH v15 1/5] ring-buffer: Flush and stop persistent ring buffer on panic

[Masami Hiramatsu (Google)]

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

On real hardware, panic and machine reboot may not flush hardware cache
to memory. This means the persistent ring buffer, which relies on a
coherent state of memory, may not have its events written to the buffer
and they may be lost. Moreover, there may be inconsistency with the
counters which are used for validation of the integrity of the
persistent ring buffer which may cause all data to be discarded.

To avoid this issue, stop recording of the ring buffer on panic and
flush the cache of the ring buffer's memory.

Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace boot instance")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v13:
   - Fix a rebase conflict.
 Changes in v11:
   - Do nothing by default since flush_cache_vmap() does nothing on x86
     but it can cause deadlock on some architectures via on_each_cpu()
     because other CPUs will be stoppped when panic notifier is called.
 Changes in v9:
   - Fix typo of & to &&.
   - Fix typo of "Generic"
 Changes in v6:
   - Introduce asm/ring_buffer.h for arch_ring_buffer_flush_range().
   - Use flush_cache_vmap() instead of flush_cache_all().
 Changes in v5:
   - Use ring_buffer_record_off() instead of ring_buffer_record_disable().
   - Use flush_cache_all() to ensure flush all cache.
 Changes in v3:
   - update patch description.
---
 arch/alpha/include/asm/Kbuild        |    1 +
 arch/arc/include/asm/Kbuild          |    1 +
 arch/arm/include/asm/Kbuild          |    1 +
 arch/arm64/include/asm/ring_buffer.h |   10 ++++++++++
 arch/csky/include/asm/Kbuild         |    1 +
 arch/hexagon/include/asm/Kbuild      |    1 +
 arch/loongarch/include/asm/Kbuild    |    1 +
 arch/m68k/include/asm/Kbuild         |    1 +
 arch/microblaze/include/asm/Kbuild   |    1 +
 arch/mips/include/asm/Kbuild         |    1 +
 arch/nios2/include/asm/Kbuild        |    1 +
 arch/openrisc/include/asm/Kbuild     |    1 +
 arch/parisc/include/asm/Kbuild       |    1 +
 arch/powerpc/include/asm/Kbuild      |    1 +
 arch/riscv/include/asm/Kbuild        |    1 +
 arch/s390/include/asm/Kbuild         |    1 +
 arch/sh/include/asm/Kbuild           |    1 +
 arch/sparc/include/asm/Kbuild        |    1 +
 arch/um/include/asm/Kbuild           |    1 +
 arch/x86/include/asm/Kbuild          |    1 +
 arch/xtensa/include/asm/Kbuild       |    1 +
 include/asm-generic/ring_buffer.h    |   13 +++++++++++++
 kernel/trace/ring_buffer.c           |   22 ++++++++++++++++++++++
 23 files changed, 65 insertions(+)
 create mode 100644 arch/arm64/include/asm/ring_buffer.h
 create mode 100644 include/asm-generic/ring_buffer.h

diff --git a/arch/alpha/include/asm/Kbuild b/arch/alpha/include/asm/Kbuild
index 483965c5a4de..b154b4e3dfa8 100644
--- a/arch/alpha/include/asm/Kbuild
+++ b/arch/alpha/include/asm/Kbuild
@@ -5,4 +5,5 @@ generic-y += agp.h
 generic-y += asm-offsets.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += text-patching.h
diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
index 4c69522e0328..483caacc6988 100644
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -5,5 +5,6 @@ generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
 generic-y += parport.h
+generic-y += ring_buffer.h
 generic-y += user.h
 generic-y += text-patching.h
diff --git a/arch/arm/include/asm/Kbuild b/arch/arm/include/asm/Kbuild
index 03657ff8fbe3..decad5f2c826 100644
--- a/arch/arm/include/asm/Kbuild
+++ b/arch/arm/include/asm/Kbuild
@@ -3,6 +3,7 @@ generic-y += early_ioremap.h
 generic-y += extable.h
 generic-y += flat.h
 generic-y += parport.h
+generic-y += ring_buffer.h
 
 generated-y += mach-types.h
 generated-y += unistd-nr.h
diff --git a/arch/arm64/include/asm/ring_buffer.h b/arch/arm64/include/asm/ring_buffer.h
new file mode 100644
index 000000000000..62316c406888
--- /dev/null
+++ b/arch/arm64/include/asm/ring_buffer.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ASM_ARM64_RING_BUFFER_H
+#define _ASM_ARM64_RING_BUFFER_H
+
+#include <asm/cacheflush.h>
+
+/* Flush D-cache on persistent ring buffer */
+#define arch_ring_buffer_flush_range(start, end)	dcache_clean_pop(start, end)
+
+#endif /* _ASM_ARM64_RING_BUFFER_H */
diff --git a/arch/csky/include/asm/Kbuild b/arch/csky/include/asm/Kbuild
index 3a5c7f6e5aac..7dca0c6cdc84 100644
--- a/arch/csky/include/asm/Kbuild
+++ b/arch/csky/include/asm/Kbuild
@@ -9,6 +9,7 @@ generic-y += qrwlock.h
 generic-y += qrwlock_types.h
 generic-y += qspinlock.h
 generic-y += parport.h
+generic-y += ring_buffer.h
 generic-y += user.h
 generic-y += vmlinux.lds.h
 generic-y += text-patching.h
diff --git a/arch/hexagon/include/asm/Kbuild b/arch/hexagon/include/asm/Kbuild
index 1efa1e993d4b..0f887d4238ed 100644
--- a/arch/hexagon/include/asm/Kbuild
+++ b/arch/hexagon/include/asm/Kbuild
@@ -5,4 +5,5 @@ generic-y += extable.h
 generic-y += iomap.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += text-patching.h
diff --git a/arch/loongarch/include/asm/Kbuild b/arch/loongarch/include/asm/Kbuild
index 9034b583a88a..7e92957baf6a 100644
--- a/arch/loongarch/include/asm/Kbuild
+++ b/arch/loongarch/include/asm/Kbuild
@@ -10,5 +10,6 @@ generic-y += qrwlock.h
 generic-y += user.h
 generic-y += ioctl.h
 generic-y += mmzone.h
+generic-y += ring_buffer.h
 generic-y += statfs.h
 generic-y += text-patching.h
diff --git a/arch/m68k/include/asm/Kbuild b/arch/m68k/include/asm/Kbuild
index b282e0dd8dc1..62543bf305ff 100644
--- a/arch/m68k/include/asm/Kbuild
+++ b/arch/m68k/include/asm/Kbuild
@@ -3,5 +3,6 @@ generated-y += syscall_table.h
 generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += spinlock.h
 generic-y += text-patching.h
diff --git a/arch/microblaze/include/asm/Kbuild b/arch/microblaze/include/asm/Kbuild
index 7178f990e8b3..0030309b47ad 100644
--- a/arch/microblaze/include/asm/Kbuild
+++ b/arch/microblaze/include/asm/Kbuild
@@ -5,6 +5,7 @@ generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
 generic-y += parport.h
+generic-y += ring_buffer.h
 generic-y += syscalls.h
 generic-y += tlb.h
 generic-y += user.h
diff --git a/arch/mips/include/asm/Kbuild b/arch/mips/include/asm/Kbuild
index 684569b2ecd6..9771c3d85074 100644
--- a/arch/mips/include/asm/Kbuild
+++ b/arch/mips/include/asm/Kbuild
@@ -12,5 +12,6 @@ generic-y += mcs_spinlock.h
 generic-y += parport.h
 generic-y += qrwlock.h
 generic-y += qspinlock.h
+generic-y += ring_buffer.h
 generic-y += user.h
 generic-y += text-patching.h
diff --git a/arch/nios2/include/asm/Kbuild b/arch/nios2/include/asm/Kbuild
index 28004301c236..0a2530964413 100644
--- a/arch/nios2/include/asm/Kbuild
+++ b/arch/nios2/include/asm/Kbuild
@@ -5,6 +5,7 @@ generic-y += cmpxchg.h
 generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += spinlock.h
 generic-y += user.h
 generic-y += text-patching.h
diff --git a/arch/openrisc/include/asm/Kbuild b/arch/openrisc/include/asm/Kbuild
index cef49d60d74c..8aa34621702d 100644
--- a/arch/openrisc/include/asm/Kbuild
+++ b/arch/openrisc/include/asm/Kbuild
@@ -8,4 +8,5 @@ generic-y += spinlock_types.h
 generic-y += spinlock.h
 generic-y += qrwlock_types.h
 generic-y += qrwlock.h
+generic-y += ring_buffer.h
 generic-y += user.h
diff --git a/arch/parisc/include/asm/Kbuild b/arch/parisc/include/asm/Kbuild
index 4fb596d94c89..d48d158f7241 100644
--- a/arch/parisc/include/asm/Kbuild
+++ b/arch/parisc/include/asm/Kbuild
@@ -4,4 +4,5 @@ generated-y += syscall_table_64.h
 generic-y += agp.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += user.h
diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild
index 2e23533b67e3..805b5aeebb6f 100644
--- a/arch/powerpc/include/asm/Kbuild
+++ b/arch/powerpc/include/asm/Kbuild
@@ -5,4 +5,5 @@ generated-y += syscall_table_spu.h
 generic-y += agp.h
 generic-y += mcs_spinlock.h
 generic-y += qrwlock.h
+generic-y += ring_buffer.h
 generic-y += early_ioremap.h
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index bd5fc9403295..7721b63642f4 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -14,5 +14,6 @@ generic-y += ticket_spinlock.h
 generic-y += qrwlock.h
 generic-y += qrwlock_types.h
 generic-y += qspinlock.h
+generic-y += ring_buffer.h
 generic-y += user.h
 generic-y += vmlinux.lds.h
diff --git a/arch/s390/include/asm/Kbuild b/arch/s390/include/asm/Kbuild
index 80bad7de7a04..0c1fc47c3ba0 100644
--- a/arch/s390/include/asm/Kbuild
+++ b/arch/s390/include/asm/Kbuild
@@ -7,3 +7,4 @@ generated-y += unistd_nr.h
 generic-y += asm-offsets.h
 generic-y += mcs_spinlock.h
 generic-y += mmzone.h
+generic-y += ring_buffer.h
diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
index 4d3f10ed8275..f0403d3ee8ab 100644
--- a/arch/sh/include/asm/Kbuild
+++ b/arch/sh/include/asm/Kbuild
@@ -3,4 +3,5 @@ generated-y += syscall_table.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
 generic-y += parport.h
+generic-y += ring_buffer.h
 generic-y += text-patching.h
diff --git a/arch/sparc/include/asm/Kbuild b/arch/sparc/include/asm/Kbuild
index 17ee8a273aa6..49c6bb326b75 100644
--- a/arch/sparc/include/asm/Kbuild
+++ b/arch/sparc/include/asm/Kbuild
@@ -4,4 +4,5 @@ generated-y += syscall_table_64.h
 generic-y += agp.h
 generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
+generic-y += ring_buffer.h
 generic-y += text-patching.h
diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
index 1b9b82bbe322..2a1629ba8140 100644
--- a/arch/um/include/asm/Kbuild
+++ b/arch/um/include/asm/Kbuild
@@ -17,6 +17,7 @@ generic-y += module.lds.h
 generic-y += parport.h
 generic-y += percpu.h
 generic-y += preempt.h
+generic-y += ring_buffer.h
 generic-y += runtime-const.h
 generic-y += softirq_stack.h
 generic-y += switch_to.h
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index 4566000e15c4..078fd2c0d69d 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -14,3 +14,4 @@ generic-y += early_ioremap.h
 generic-y += fprobe.h
 generic-y += mcs_spinlock.h
 generic-y += mmzone.h
+generic-y += ring_buffer.h
diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild
index 13fe45dea296..e57af619263a 100644
--- a/arch/xtensa/include/asm/Kbuild
+++ b/arch/xtensa/include/asm/Kbuild
@@ -6,5 +6,6 @@ generic-y += mcs_spinlock.h
 generic-y += parport.h
 generic-y += qrwlock.h
 generic-y += qspinlock.h
+generic-y += ring_buffer.h
 generic-y += user.h
 generic-y += text-patching.h
diff --git a/include/asm-generic/ring_buffer.h b/include/asm-generic/ring_buffer.h
new file mode 100644
index 000000000000..201d2aee1005
--- /dev/null
+++ b/include/asm-generic/ring_buffer.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Generic arch dependent ring_buffer macros.
+ */
+#ifndef __ASM_GENERIC_RING_BUFFER_H__
+#define __ASM_GENERIC_RING_BUFFER_H__
+
+#include <linux/cacheflush.h>
+
+/* Flush cache on ring buffer range if needed. Do nothing by default. */
+#define arch_ring_buffer_flush_range(start, end)	do { } while (0)
+
+#endif /* __ASM_GENERIC_RING_BUFFER_H__ */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 8b6c39bba56d..3e793bd1c134 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -7,6 +7,7 @@
 #include <linux/ring_buffer_types.h>
 #include <linux/sched/isolation.h>
 #include <linux/trace_recursion.h>
+#include <linux/panic_notifier.h>
 #include <linux/trace_events.h>
 #include <linux/ring_buffer.h>
 #include <linux/trace_clock.h>
@@ -31,6 +32,7 @@
 #include <linux/oom.h>
 #include <linux/mm.h>
 
+#include <asm/ring_buffer.h>
 #include <asm/local64.h>
 #include <asm/local.h>
 #include <asm/setup.h>
@@ -559,6 +561,7 @@ struct trace_buffer {
 
 	unsigned long			range_addr_start;
 	unsigned long			range_addr_end;
+	struct notifier_block		flush_nb;
 
 	struct ring_buffer_meta		*meta;
 
@@ -2520,6 +2523,16 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 	kfree(cpu_buffer);
 }
 
+/* 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);
+	arch_ring_buffer_flush_range(buffer->range_addr_start, buffer->range_addr_end);
+	return NOTIFY_DONE;
+}
+
 static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 					 int order, unsigned long start,
 					 unsigned long end,
@@ -2650,6 +2663,12 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 
 	mutex_init(&buffer->mutex);
 
+	/* Persistent ring buffer needs to flush cache before reboot. */
+	if (start && end) {
+		buffer->flush_nb.notifier_call = rb_flush_buffer_cb;
+		atomic_notifier_chain_register(&panic_notifier_list, &buffer->flush_nb);
+	}
+
 	return_ptr(buffer);
 
  fail_free_buffers:
@@ -2748,6 +2767,9 @@ ring_buffer_free(struct trace_buffer *buffer)
 {
 	int cpu;
 
+	if (buffer->range_addr_start && buffer->range_addr_end)
+		atomic_notifier_chain_unregister(&panic_notifier_list, &buffer->flush_nb);
+
 	cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
 
 	irq_work_sync(&buffer->irq_work.work);

[PATCH v15 2/5] ring-buffer: Skip invalid sub-buffers when validating persistent ring buffer

[Masami Hiramatsu (Google)]

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

Skip invalid sub-buffers when validating the persistent ring buffer
instead of discarding the entire ring buffer. Only skipped buffers
are invalidated (cleared).

If the cache data in memory fails to be synchronized during a reboot,
the persistent ring buffer may become partially corrupted, but other
sub-buffers may still contain readable event data. Only discard the
subbuffers that are found to be corrupted.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
  Changes in v15:
  - Skip reader_page loop check on persistent ring buffer because
    there can be contiguous empty(invalidated) pages.
  - Do not show discarded page number information if it is 0.
  Changes in v11:
  - Fix a typo.
  Changes in v9:
  - Add meta->subbuf_size check.
  - Fix a typo.
  - Handle invalid reader_page case.
  Changes in v8:
  - Add comment in rb_valudate_buffer()
  - Clear the RB_MISSED_* flags in rb_valudate_buffer() instead of
    skipping subbuf.
  - Remove unused subbuf local variable from rb_cpu_meta_valid().
  Changes in v7:
  - Combined with Handling RB_MISSED_* flags patch, focus on validation at boot.
  - Remove checking subbuffer data when validating metadata, because it should be done
    later.
  - Do not mark the discarded sub buffer page but just reset it.
  Changes in v6:
  - Show invalid page detection message once per CPU.
  Changes in v5:
  - Instead of showing errors for each page, just show the number
    of discarded pages at last.
  Changes in v3:
  - Record missed data event on commit.
---
 kernel/trace/ring_buffer.c |  109 ++++++++++++++++++++++++++------------------
 1 file changed, 65 insertions(+), 44 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3e793bd1c134..2a6254edae5f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -370,6 +370,12 @@ static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
 	return local_read(&bpage->page->commit);
 }
 
+/* Size is determined by what has been committed */
+static __always_inline unsigned int rb_page_size(struct buffer_page *bpage)
+{
+	return rb_page_commit(bpage) & ~RB_MISSED_MASK;
+}
+
 static void free_buffer_page(struct buffer_page *bpage)
 {
 	/* Range pages are not to be freed */
@@ -1762,7 +1768,6 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 			      unsigned long *subbuf_mask)
 {
 	int subbuf_size = PAGE_SIZE;
-	struct buffer_data_page *subbuf;
 	unsigned long buffers_start;
 	unsigned long buffers_end;
 	int i;
@@ -1770,6 +1775,11 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 	if (!subbuf_mask)
 		return false;
 
+	if (meta->subbuf_size != PAGE_SIZE) {
+		pr_info("Ring buffer boot meta [%d] invalid subbuf_size\n", cpu);
+		return false;
+	}
+
 	buffers_start = meta->first_buffer;
 	buffers_end = meta->first_buffer + (subbuf_size * meta->nr_subbufs);
 
@@ -1786,11 +1796,12 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 		return false;
 	}
 
-	subbuf = rb_subbufs_from_meta(meta);
-
 	bitmap_clear(subbuf_mask, 0, meta->nr_subbufs);
 
-	/* Is the meta buffers and the subbufs themselves have correct data? */
+	/*
+	 * Ensure the meta::buffers array has correct data. The data in each subbufs
+	 * are checked later in rb_meta_validate_events().
+	 */
 	for (i = 0; i < meta->nr_subbufs; i++) {
 		if (meta->buffers[i] < 0 ||
 		    meta->buffers[i] >= meta->nr_subbufs) {
@@ -1798,18 +1809,12 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 			return false;
 		}
 
-		if ((unsigned)local_read(&subbuf->commit) > subbuf_size) {
-			pr_info("Ring buffer boot meta [%d] buffer invalid commit\n", cpu);
-			return false;
-		}
-
 		if (test_bit(meta->buffers[i], subbuf_mask)) {
 			pr_info("Ring buffer boot meta [%d] array has duplicates\n", cpu);
 			return false;
 		}
 
 		set_bit(meta->buffers[i], subbuf_mask);
-		subbuf = (void *)subbuf + subbuf_size;
 	}
 
 	return true;
@@ -1873,13 +1878,22 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
 	return events;
 }
 
-static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu)
+static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu,
+			      struct ring_buffer_cpu_meta *meta)
 {
 	unsigned long long ts;
+	unsigned long tail;
 	u64 delta;
-	int tail;
 
-	tail = local_read(&dpage->commit);
+	/*
+	 * When a sub-buffer is recovered from a read, the commit value may
+	 * have RB_MISSED_* bits set, as these bits are reset on reuse.
+	 * Even after clearing these bits, a commit value greater than the
+	 * subbuf_size is considered invalid.
+	 */
+	tail = local_read(&dpage->commit) & ~RB_MISSED_MASK;
+	if (tail > meta->subbuf_size)
+		return -1;
 	return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
 }
 
@@ -1890,6 +1904,7 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	struct buffer_page *head_page, *orig_head;
 	unsigned long entry_bytes = 0;
 	unsigned long entries = 0;
+	int discarded = 0;
 	int ret;
 	u64 ts;
 	int i;
@@ -1900,14 +1915,19 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	orig_head = head_page = cpu_buffer->head_page;
 
 	/* Do the reader page first */
-	ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu);
+	ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu, meta);
 	if (ret < 0) {
-		pr_info("Ring buffer reader page is invalid\n");
-		goto invalid;
+		pr_info("Ring buffer meta [%d] invalid reader page detected\n",
+			cpu_buffer->cpu);
+		discarded++;
+		/* Instead of discard whole ring buffer, discard only this sub-buffer. */
+		local_set(&cpu_buffer->reader_page->entries, 0);
+		local_set(&cpu_buffer->reader_page->page->commit, 0);
+	} else {
+		entries += ret;
+		entry_bytes += rb_page_size(cpu_buffer->reader_page);
+		local_set(&cpu_buffer->reader_page->entries, ret);
 	}
-	entries += ret;
-	entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
-	local_set(&cpu_buffer->reader_page->entries, ret);
 
 	ts = head_page->page->time_stamp;
 
@@ -1935,7 +1955,7 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 			break;
 
 		/* Stop rewind if the page is invalid. */
-		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu);
+		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu, meta);
 		if (ret < 0)
 			break;
 
@@ -2014,21 +2034,24 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 		if (head_page == cpu_buffer->reader_page)
 			continue;
 
-		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu);
+		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu, meta);
 		if (ret < 0) {
-			pr_info("Ring buffer meta [%d] invalid buffer page\n",
-				cpu_buffer->cpu);
-			goto invalid;
-		}
-
-		/* If the buffer has content, update pages_touched */
-		if (ret)
-			local_inc(&cpu_buffer->pages_touched);
-
-		entries += ret;
-		entry_bytes += local_read(&head_page->page->commit);
-		local_set(&head_page->entries, ret);
+			if (!discarded)
+				pr_info("Ring buffer meta [%d] invalid buffer page detected\n",
+					cpu_buffer->cpu);
+			discarded++;
+			/* Instead of discard whole ring buffer, discard only this sub-buffer. */
+			local_set(&head_page->entries, 0);
+			local_set(&head_page->page->commit, 0);
+		} else {
+			/* If the buffer has content, update pages_touched */
+			if (ret)
+				local_inc(&cpu_buffer->pages_touched);
 
+			entries += ret;
+			entry_bytes += rb_page_size(head_page);
+			local_set(&head_page->entries, ret);
+		}
 		if (head_page == cpu_buffer->commit_page)
 			break;
 	}
@@ -2042,7 +2065,10 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	local_set(&cpu_buffer->entries, entries);
 	local_set(&cpu_buffer->entries_bytes, entry_bytes);
 
-	pr_info("Ring buffer meta [%d] is from previous boot!\n", cpu_buffer->cpu);
+	pr_info("Ring buffer meta [%d] is from previous boot!", cpu_buffer->cpu);
+	if (discarded)
+		pr_cont(" (%d pages discarded)", discarded);
+	pr_cont("\n");
 	return;
 
  invalid:
@@ -3329,12 +3355,6 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
 	return NULL;
 }
 
-/* Size is determined by what has been committed */
-static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
-{
-	return rb_page_commit(bpage) & ~RB_MISSED_MASK;
-}
-
 static __always_inline unsigned
 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
 {
@@ -5647,11 +5667,12 @@ __rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
  again:
 	/*
 	 * This should normally only loop twice. But because the
-	 * start of the reader inserts an empty page, it causes
-	 * a case where we will loop three times. There should be no
-	 * reason to loop four times (that I know of).
+	 * start of the reader inserts an empty page, it causes a
+	 * case where we will loop three times. There should be no
+	 * reason to loop four times unless the ring buffer is a
+	 * recovered persistent ring buffer.
 	 */
-	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
+	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3 && !cpu_buffer->ring_meta)) {
 		reader = NULL;
 		goto out;
 	}

[PATCH v15 3/5] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer

[Masami Hiramatsu (Google)]

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

Skip invalid sub-buffers when rewinding the persistent ring buffer
instead of stopping the rewinding the ring buffer. The skipped
buffers are cleared.

To ensure the rewinding stops at the unused page, this also clears
buffer_data_page::time_stamp when tracing resets the buffer. This
allows us to identify unused pages and empty pages.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v12:
   - Fix build error.
 Changes in v11:
   - Reset timestamp when the buffer is invalid.
   - When rewinding, skip subbuf page if timestamp is wrong and
     check timestamp after validating buffer data page.
 Changes in v10:
   - Newly added.
---
 kernel/trace/ring_buffer.c |   76 +++++++++++++++++++++++++-------------------
 1 file changed, 43 insertions(+), 33 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2a6254edae5f..5ff632ca3858 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -363,6 +363,7 @@ struct buffer_page {
 static void rb_init_page(struct buffer_data_page *bpage)
 {
 	local_set(&bpage->commit, 0);
+	bpage->time_stamp = 0;
 }
 
 static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
@@ -1878,12 +1879,14 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
 	return events;
 }
 
-static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu,
+static int rb_validate_buffer(struct buffer_page *bpage, int cpu,
 			      struct ring_buffer_cpu_meta *meta)
 {
+	struct buffer_data_page *dpage = bpage->page;
 	unsigned long long ts;
 	unsigned long tail;
 	u64 delta;
+	int ret = -1;
 
 	/*
 	 * When a sub-buffer is recovered from a read, the commit value may
@@ -1892,9 +1895,17 @@ static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu,
 	 * subbuf_size is considered invalid.
 	 */
 	tail = local_read(&dpage->commit) & ~RB_MISSED_MASK;
-	if (tail > meta->subbuf_size)
-		return -1;
-	return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
+	if (tail <= meta->subbuf_size)
+		ret = rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
+
+	if (ret < 0) {
+		local_set(&bpage->entries, 0);
+		local_set(&bpage->page->commit, 0);
+	} else {
+		local_set(&bpage->entries, ret);
+	}
+
+	return ret;
 }
 
 /* If the meta data has been validated, now validate the events */
@@ -1915,18 +1926,14 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	orig_head = head_page = cpu_buffer->head_page;
 
 	/* Do the reader page first */
-	ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu, meta);
+	ret = rb_validate_buffer(cpu_buffer->reader_page, cpu_buffer->cpu, meta);
 	if (ret < 0) {
 		pr_info("Ring buffer meta [%d] invalid reader page detected\n",
 			cpu_buffer->cpu);
 		discarded++;
-		/* Instead of discard whole ring buffer, discard only this sub-buffer. */
-		local_set(&cpu_buffer->reader_page->entries, 0);
-		local_set(&cpu_buffer->reader_page->page->commit, 0);
 	} else {
 		entries += ret;
 		entry_bytes += rb_page_size(cpu_buffer->reader_page);
-		local_set(&cpu_buffer->reader_page->entries, ret);
 	}
 
 	ts = head_page->page->time_stamp;
@@ -1945,26 +1952,33 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 		if (head_page == cpu_buffer->tail_page)
 			break;
 
-		/* Ensure the page has older data than head. */
-		if (ts < head_page->page->time_stamp)
-			break;
-
-		ts = head_page->page->time_stamp;
-		/* Ensure the page has correct timestamp and some data. */
-		if (!ts || rb_page_commit(head_page) == 0)
-			break;
-
-		/* Stop rewind if the page is invalid. */
-		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu, meta);
-		if (ret < 0)
+		/* Rewind until unused page (no timestamp, no commit). */
+		if (!head_page->page->time_stamp && rb_page_commit(head_page) == 0)
 			break;
 
-		/* Recover the number of entries and update stats. */
-		local_set(&head_page->entries, ret);
-		if (ret)
-			local_inc(&cpu_buffer->pages_touched);
-		entries += ret;
-		entry_bytes += rb_page_commit(head_page);
+		/*
+		 * Skip if the page is invalid, or its timestamp is newer than the
+		 * previous valid page.
+		 */
+		ret = rb_validate_buffer(head_page, cpu_buffer->cpu, meta);
+		if (ret >= 0 && ts < head_page->page->time_stamp) {
+			local_set(&head_page->entries, 0);
+			local_set(&head_page->page->commit, 0);
+			head_page->page->time_stamp = ts;
+			ret = -1;
+		}
+		if (ret < 0) {
+			if (!discarded)
+				pr_info("Ring buffer meta [%d] invalid buffer page detected\n",
+					cpu_buffer->cpu);
+			discarded++;
+		} else {
+			entries += ret;
+			entry_bytes += rb_page_size(head_page);
+			if (ret > 0)
+				local_inc(&cpu_buffer->pages_touched);
+			ts = head_page->page->time_stamp;
+		}
 	}
 	if (i)
 		pr_info("Ring buffer [%d] rewound %d pages\n", cpu_buffer->cpu, i);
@@ -2034,15 +2048,12 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 		if (head_page == cpu_buffer->reader_page)
 			continue;
 
-		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu, meta);
+		ret = rb_validate_buffer(head_page, cpu_buffer->cpu, meta);
 		if (ret < 0) {
 			if (!discarded)
 				pr_info("Ring buffer meta [%d] invalid buffer page detected\n",
 					cpu_buffer->cpu);
 			discarded++;
-			/* Instead of discard whole ring buffer, discard only this sub-buffer. */
-			local_set(&head_page->entries, 0);
-			local_set(&head_page->page->commit, 0);
 		} else {
 			/* If the buffer has content, update pages_touched */
 			if (ret)
@@ -2050,7 +2061,6 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 
 			entries += ret;
 			entry_bytes += rb_page_size(head_page);
-			local_set(&head_page->entries, ret);
 		}
 		if (head_page == cpu_buffer->commit_page)
 			break;
@@ -2083,7 +2093,7 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	/* Reset all the subbuffers */
 	for (i = 0; i < meta->nr_subbufs - 1; i++, rb_inc_page(&head_page)) {
 		local_set(&head_page->entries, 0);
-		local_set(&head_page->page->commit, 0);
+		rb_init_page(head_page->page);
 	}
 }
 

[PATCH v15 4/5] ring-buffer: Add persistent ring buffer invalid-page inject test

[Masami Hiramatsu (Google)]

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

Add a self-destractive test for the persistent ring buffer.

This will inject erroneous value to some sub-buffer pages (where
the index is even or multiples of 5) in the persistent ring buffer
when kernel gets panic, and check whether the number of detected
invalid pages and the total entry_bytes are the same as recorded
values 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_INJECT
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 [2] invalid buffer page detected
 Ring buffer meta [2] is from previous boot! (318 pages discarded)
 Ring buffer testing [2] invalid pages: PASSED (318/318)
 Ring buffer testing [2] entry_bytes: PASSED (1300476/1300476)

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v15:
  - Use pr_warn() for test result.
  - Inject errors on the page index is multiples of 5 so that
    this can reproduce contiguous empty pages.
 Changes in v14:
  - Rename config to CONFIG_RING_BUFFER_PERSISTENT_INJECT.
  - Clear meta->nr_invalid/entry_bytes after testing.
  - Add test commands in config comment.
 Changes in v10:
  - Add entry_bytes test.
  - Do not compile test code if CONFIG_RING_BUFFER_PERSISTENT_SELFTEST=n.
 Changes in v9:
  - Test also reader pages.
---
 include/linux/ring_buffer.h |    1 +
 kernel/trace/Kconfig        |   31 ++++++++++++++++++
 kernel/trace/ring_buffer.c  |   74 +++++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace.c        |    4 ++
 4 files changed, 110 insertions(+)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 994f52b34344..0670742b2d60 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 e130da35808f..07305ed6d745 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1202,6 +1202,37 @@ 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_INJECT
+	bool "Enable persistent ring buffer error injection test"
+	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.
+	  To use this, boot kernel with "ptracingtest" persistent
+	  ring buffer, e.g.
+
+	   reserve_mem=20M:2M:trace trace_instance=ptracingtest@trace panic=1
+
+	  And after the 1st boot, run test command, like;
+
+	   cd /sys/kernel/tracing/instances/ptracingtest
+	   echo 1 > events/enable
+	   echo 1 > tracing_on
+	   sleep 3
+	   echo c > /proc/sysrq-trigger
+
+	  After panic message, the kernel reboots and show test results
+	  on the boot log.
+
+	  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 5ff632ca3858..fb098b0b4505 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -64,6 +64,10 @@ struct ring_buffer_cpu_meta {
 	unsigned long	commit_buffer;
 	__u32		subbuf_size;
 	__u32		nr_subbufs;
+#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
+	__u32		nr_invalid;
+	__u32		entry_bytes;
+#endif
 	int		buffers[];
 };
 
@@ -2079,6 +2083,21 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	if (discarded)
 		pr_cont(" (%d pages discarded)", discarded);
 	pr_cont("\n");
+
+#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
+	if (meta->nr_invalid)
+		pr_warn("Ring buffer testing [%d] invalid pages: %s (%d/%d)\n",
+			cpu_buffer->cpu,
+			(discarded == meta->nr_invalid) ? "PASSED" : "FAILED",
+			discarded, meta->nr_invalid);
+	if (meta->entry_bytes)
+		pr_warn("Ring buffer testing [%d] entry_bytes: %s (%ld/%ld)\n",
+			cpu_buffer->cpu,
+			(entry_bytes == meta->entry_bytes) ? "PASSED" : "FAILED",
+			(long)entry_bytes, (long)meta->entry_bytes);
+	meta->nr_invalid = 0;
+	meta->entry_bytes = 0;
+#endif
 	return;
 
  invalid:
@@ -2559,12 +2578,67 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 	kfree(cpu_buffer);
 }
 
+#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
+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;
+	u32 entry_bytes = 0;
+	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;
+
+	for (i = 0; i < meta->nr_subbufs; i++) {
+		int idx = meta->buffers[i];
+
+		dpage = (void *)(ptr + idx * subbuf_size);
+		/* Skip unused pages */
+		if (!local_read(&dpage->commit))
+			continue;
+
+		/*
+		 * Invalidate even pages or multiples of 5. This will lead 3
+		 * contiguous invalidated(empty) pages.
+		 */
+		if (!(i & 0x1) || !(i % 5)) {
+			local_add(subbuf_size + 1, &dpage->commit);
+			invalid++;
+		} else {
+			/* Count total commit bytes. */
+			entry_bytes += local_read(&dpage->commit);
+		}
+	}
+
+	pr_info("Inject invalidated %d pages on CPU%d, total size: %ld\n",
+		invalid, cpu, (long)entry_bytes);
+	meta->nr_invalid = invalid;
+	meta->entry_bytes = entry_bytes;
+}
+#else /* !CONFIG_RING_BUFFER_PERSISTENT_INJECT */
+#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 4189ec9df6a5..108b0d16badf 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9366,6 +9366,8 @@ 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, unsigned long size)
 {
@@ -9378,6 +9380,8 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, unsigned
 	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,

[PATCH v15 5/5] ring-buffer: Show commit numbers in buffer_meta file

[Masami Hiramatsu (Google)]

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

In addition to the index number, show the commit numbers of
each data page in per_cpu buffer_meta file.
This is useful for understanding the current status of the
persistent ring buffer. (Note that this file is shown
only for persistent ring buffer and its backup instance)

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/ring_buffer.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fb098b0b4505..5b40fea6b15d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2209,6 +2209,7 @@ static int rbm_show(struct seq_file *m, void *v)
 	struct ring_buffer_per_cpu *cpu_buffer = m->private;
 	struct ring_buffer_cpu_meta *meta = cpu_buffer->ring_meta;
 	unsigned long val = (unsigned long)v;
+	struct buffer_data_page *dpage;
 
 	if (val == 1) {
 		seq_printf(m, "head_buffer:   %d\n",
@@ -2221,7 +2222,9 @@ static int rbm_show(struct seq_file *m, void *v)
 	}
 
 	val -= 2;
-	seq_printf(m, "buffer[%ld]:    %d\n", val, meta->buffers[val]);
+	dpage = rb_range_buffer(cpu_buffer, val);
+	seq_printf(m, "buffer[%ld]:    %d (commit: %ld)\n",
+		   val, meta->buffers[val], local_read(&dpage->commit));
 
 	return 0;
 }

Re: [PATCH v15 1/5] ring-buffer: Flush and stop persistent ring buffer on panic

[Catalin Marinas]

On Tue, Mar 31, 2026 at 05:36:06PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> On real hardware, panic and machine reboot may not flush hardware cache
> to memory. This means the persistent ring buffer, which relies on a
> coherent state of memory, may not have its events written to the buffer
> and they may be lost. Moreover, there may be inconsistency with the
> counters which are used for validation of the integrity of the
> persistent ring buffer which may cause all data to be discarded.
> 
> To avoid this issue, stop recording of the ring buffer on panic and
> flush the cache of the ring buffer's memory.
> 
> Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace boot instance")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
[...]
> diff --git a/arch/arm64/include/asm/ring_buffer.h b/arch/arm64/include/asm/ring_buffer.h
> new file mode 100644
> index 000000000000..62316c406888
> --- /dev/null
> +++ b/arch/arm64/include/asm/ring_buffer.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef _ASM_ARM64_RING_BUFFER_H
> +#define _ASM_ARM64_RING_BUFFER_H
> +
> +#include <asm/cacheflush.h>
> +
> +/* Flush D-cache on persistent ring buffer */
> +#define arch_ring_buffer_flush_range(start, end)	dcache_clean_pop(start, end)
> +
> +#endif /* _ASM_ARM64_RING_BUFFER_H */

Adding Robin as he wrote the pmem support for arm64.

I assume the ring buffer here is cacheable memory, otherwise we'd also
need a dmb(osh) as in arch_wb_cache_pmem(). If that's correct:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v15 1/5] ring-buffer: Flush and stop persistent ring buffer on panic

[Steven Rostedt]

On Tue, 31 Mar 2026 18:57:13 +0100
Catalin Marinas <catalin.marinas@arm.com> wrote:

> I assume the ring buffer here is cacheable memory, otherwise we'd also
> need a dmb(osh) as in arch_wb_cache_pmem(). If that's correct:

Yes, it's cacheable (I couldn't imagine the performance overhead if it
wasn't! ;-)

> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Thanks!

-- Steve

Re: [PATCH v15 4/5] ring-buffer: Add persistent ring buffer invalid-page inject test

[Steven Rostedt]

I replied with mostly grammar fixes and some rewrites of text.

On Tue, 31 Mar 2026 17:36:30 +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.

  "self-destractive"? Do you mean "self-destructive"?

Probably better to call it a "self-corrupting test".

> 
> This will inject erroneous value to some sub-buffer pages (where

            inject an erroneous

> the index is even or multiples of 5) in the persistent ring buffer
> when kernel gets panic, and check whether the number of detected

  when the kernel panics, and checks whether

> invalid pages and the total entry_bytes are the same as recorded

                                                  same as the recorded

> values after reboot.
> 
> This can ensure the kernel correctly recover partially corrupted

  This ensures that the kernel can correctly recover a partially corrupted

> persistent ring buffer when boot.

                         after a reboot or panic.

> 
> The test only runs on the persistent ring buffer whose name is
> "ptracingtest". And user has to fill it up with events before

                  The user has to fill it with events before a kernel panic.

> kernel panics.
> 
> To run the test, enable CONFIG_RING_BUFFER_PERSISTENT_INJECT
> and you have to setup the kernel cmdline;

  and add the following kernel cmdline:

Note, it's more proper to use a colon (:) than a semi-colon (;) when
referencing an example on the next line.

> 
>  reserve_mem=20M:2M:trace trace_instance=ptracingtest^traceoff@trace
>  panic=1
> 
> And run following commands after the 1st boot;

  Run the 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 [2] invalid buffer page detected
>  Ring buffer meta [2] is from previous boot! (318 pages discarded)
>  Ring buffer testing [2] invalid pages: PASSED (318/318)
>  Ring buffer testing [2] entry_bytes: PASSED (1300476/1300476)
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  Changes in v15:
>   - Use pr_warn() for test result.
>   - Inject errors on the page index is multiples of 5 so that
>     this can reproduce contiguous empty pages.
>  Changes in v14:
>   - Rename config to CONFIG_RING_BUFFER_PERSISTENT_INJECT.
>   - Clear meta->nr_invalid/entry_bytes after testing.
>   - Add test commands in config comment.
>  Changes in v10:
>   - Add entry_bytes test.
>   - Do not compile test code if CONFIG_RING_BUFFER_PERSISTENT_SELFTEST=n.
>  Changes in v9:
>   - Test also reader pages.
> ---
>  include/linux/ring_buffer.h |    1 +
>  kernel/trace/Kconfig        |   31 ++++++++++++++++++
>  kernel/trace/ring_buffer.c  |   74 +++++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace.c        |    4 ++
>  4 files changed, 110 insertions(+)
> 
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index 994f52b34344..0670742b2d60 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 e130da35808f..07305ed6d745 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -1202,6 +1202,37 @@ 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_INJECT
> +	bool "Enable persistent ring buffer error injection test"
> +	depends on RING_BUFFER
> +	help
> +	  Run a selftest on the persistent ring buffer which names
> +	  "ptracingtest" (and its backup) when panic_on_reboot by

  Does this do anything with the backup?

> +	  invalidating ring buffer pages.

 	  This option will have the kernel check if the persistent ring
 	  buffer is named "ptracingtest", and if so, it will corrupt some
 	  of its pages on a kernel panic. This is used to test if the
 	  persistent ring buffer can recover from some of its sub-buffers
 	  being corrupted.

[space]

> +	  To use this, boot kernel with "ptracingtest" persistent

                     , boot a kernel with a "ptracingtest" persistent

> +	  ring buffer, e.g.
> +
> +	   reserve_mem=20M:2M:trace trace_instance=ptracingtest@trace panic=1
> +
> +	  And after the 1st boot, run test command, like;

                               , run the following commands:

> +
> +	   cd /sys/kernel/tracing/instances/ptracingtest
> +	   echo 1 > events/enable
> +	   echo 1 > tracing_on
> +	   sleep 3
> +	   echo c > /proc/sysrq-trigger
> +
> +	  After panic message, the kernel reboots and show test results
> +	  on the boot log.

          After the panic message, the kernel will reboot and will show the
          test results in the console output.

> +
> +	  Note that user has to enable events on the persistent ring
> +	  buffer manually to fill up ring buffers before rebooting.

	  Note that events for the ring buffer needs to be enabled prior to
	  crashing the kernel so that the ring buffer has content that the
	  test will corrupt.

> +	  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.

	  As the test will corrupt events in the "ptracingtest" persistent
	  ring buffer, it should not be used for any other purpose other
	  than his test.


> +
> +	  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 5ff632ca3858..fb098b0b4505 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -64,6 +64,10 @@ struct ring_buffer_cpu_meta {
>  	unsigned long	commit_buffer;
>  	__u32		subbuf_size;
>  	__u32		nr_subbufs;
> +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> +	__u32		nr_invalid;
> +	__u32		entry_bytes;
> +#endif
>  	int		buffers[];
>  };
>  
> @@ -2079,6 +2083,21 @@ static void rb_meta_validate_events(struct
> 	  ring_buffer_per_cpu *cpu_buffer) if (discarded)
>  		pr_cont(" (%d pages discarded)", discarded);
>  	pr_cont("\n");
> +
> +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> +	if (meta->nr_invalid)
> +		pr_warn("Ring buffer testing [%d] invalid pages: %s (%d/%d)\n",
> +			cpu_buffer->cpu,
> +			(discarded == meta->nr_invalid) ? "PASSED" : "FAILED",
> +			discarded, meta->nr_invalid);
> +	if (meta->entry_bytes)
> +		pr_warn("Ring buffer testing [%d] entry_bytes: %s (%ld/%ld)\n",
> +			cpu_buffer->cpu,
> +			(entry_bytes == meta->entry_bytes) ? "PASSED" : "FAILED",
> +			(long)entry_bytes, (long)meta->entry_bytes);
> +	meta->nr_invalid = 0;
> +	meta->entry_bytes = 0;
> +#endif
>  	return;
>  
>   invalid:
> @@ -2559,12 +2578,67 @@ static void rb_free_cpu_buffer(struct
> 	  ring_buffer_per_cpu *cpu_buffer) kfree(cpu_buffer);
>  }
>  
> +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> +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;
> +	u32 entry_bytes = 0;
> +	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;
> +
> +	for (i = 0; i < meta->nr_subbufs; i++) {
> +		int idx = meta->buffers[i];
> +
> +		dpage = (void *)(ptr + idx * subbuf_size);
> +		/* Skip unused pages */
> +		if (!local_read(&dpage->commit))
> +			continue;
> +
> +		/*
> +		 * Invalidate even pages or multiples of 5. This will lead 3

							    This will cause 3

-- Steve

> +		 * contiguous invalidated(empty) pages.
> +		 */
> +		if (!(i & 0x1) || !(i % 5)) {
> +			local_add(subbuf_size + 1, &dpage->commit);
> +			invalid++;
> +		} else {
> +			/* Count total commit bytes. */
> +			entry_bytes += local_read(&dpage->commit);
> +		}
> +	}
> +
> +	pr_info("Inject invalidated %d pages on CPU%d, total size: %ld\n",
> +		invalid, cpu, (long)entry_bytes);
> +	meta->nr_invalid = invalid;
> +	meta->entry_bytes = entry_bytes;
> +}

Re: [PATCH v15 5/5] ring-buffer: Show commit numbers in buffer_meta file

[Steven Rostedt]

On Tue, 31 Mar 2026 17:36:38 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> In addition to the index number, show the commit numbers of
> each data page in per_cpu buffer_meta file.

                 in the per_cpu buffer_meta file.

-- Steve

> This is useful for understanding the current status of the
> persistent ring buffer. (Note that this file is shown
> only for persistent ring buffer and its backup instance)
> 

Re: [PATCH v15 4/5] ring-buffer: Add persistent ring buffer invalid-page inject test

[Masami Hiramatsu]

On Wed, 1 Apr 2026 18:40:55 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> 
> I replied with mostly grammar fixes and some rewrites of text.

Thanks for reviewing! Let me update it.

> 
> On Tue, 31 Mar 2026 17:36:30 +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.
> 
>   "self-destractive"? Do you mean "self-destructive"?
> 
> Probably better to call it a "self-corrupting test".
> 
> > 
> > This will inject erroneous value to some sub-buffer pages (where
> 
>             inject an erroneous
> 
> > the index is even or multiples of 5) in the persistent ring buffer
> > when kernel gets panic, and check whether the number of detected
> 
>   when the kernel panics, and checks whether
> 
> > invalid pages and the total entry_bytes are the same as recorded
> 
>                                                   same as the recorded
> 
> > values after reboot.
> > 
> > This can ensure the kernel correctly recover partially corrupted
> 
>   This ensures that the kernel can correctly recover a partially corrupted
> 
> > persistent ring buffer when boot.
> 
>                          after a reboot or panic.
> 
> > 
> > The test only runs on the persistent ring buffer whose name is
> > "ptracingtest". And user has to fill it up with events before
> 
>                   The user has to fill it with events before a kernel panic.
> 
> > kernel panics.
> > 
> > To run the test, enable CONFIG_RING_BUFFER_PERSISTENT_INJECT
> > and you have to setup the kernel cmdline;
> 
>   and add the following kernel cmdline:
> 
> Note, it's more proper to use a colon (:) than a semi-colon (;) when
> referencing an example on the next line.

OK, 

> 
> > 
> >  reserve_mem=20M:2M:trace trace_instance=ptracingtest^traceoff@trace
> >  panic=1
> > 
> > And run following commands after the 1st boot;
> 
>   Run the 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 [2] invalid buffer page detected
> >  Ring buffer meta [2] is from previous boot! (318 pages discarded)
> >  Ring buffer testing [2] invalid pages: PASSED (318/318)
> >  Ring buffer testing [2] entry_bytes: PASSED (1300476/1300476)
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---
> >  Changes in v15:
> >   - Use pr_warn() for test result.
> >   - Inject errors on the page index is multiples of 5 so that
> >     this can reproduce contiguous empty pages.
> >  Changes in v14:
> >   - Rename config to CONFIG_RING_BUFFER_PERSISTENT_INJECT.
> >   - Clear meta->nr_invalid/entry_bytes after testing.
> >   - Add test commands in config comment.
> >  Changes in v10:
> >   - Add entry_bytes test.
> >   - Do not compile test code if CONFIG_RING_BUFFER_PERSISTENT_SELFTEST=n.
> >  Changes in v9:
> >   - Test also reader pages.
> > ---
> >  include/linux/ring_buffer.h |    1 +
> >  kernel/trace/Kconfig        |   31 ++++++++++++++++++
> >  kernel/trace/ring_buffer.c  |   74 +++++++++++++++++++++++++++++++++++++++++++
> >  kernel/trace/trace.c        |    4 ++
> >  4 files changed, 110 insertions(+)
> > 
> > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> > index 994f52b34344..0670742b2d60 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 e130da35808f..07305ed6d745 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -1202,6 +1202,37 @@ 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_INJECT
> > +	bool "Enable persistent ring buffer error injection test"
> > +	depends on RING_BUFFER
> > +	help
> > +	  Run a selftest on the persistent ring buffer which names
> > +	  "ptracingtest" (and its backup) when panic_on_reboot by
> 
>   Does this do anything with the backup?

This meant that if you make a backup of ptracingtest
(instance=backup=ptracingtest) the check runs on backup instance too.
But it may be redundant. I'll drop it.

> 
> > +	  invalidating ring buffer pages.
> 
>  	  This option will have the kernel check if the persistent ring
>  	  buffer is named "ptracingtest", and if so, it will corrupt some
>  	  of its pages on a kernel panic. This is used to test if the
>  	  persistent ring buffer can recover from some of its sub-buffers
>  	  being corrupted.
> 
> [space]
> 
> > +	  To use this, boot kernel with "ptracingtest" persistent
> 
>                      , boot a kernel with a "ptracingtest" persistent
> 
> > +	  ring buffer, e.g.
> > +
> > +	   reserve_mem=20M:2M:trace trace_instance=ptracingtest@trace panic=1
> > +
> > +	  And after the 1st boot, run test command, like;
> 
>                                , run the following commands:
> 
> > +
> > +	   cd /sys/kernel/tracing/instances/ptracingtest
> > +	   echo 1 > events/enable
> > +	   echo 1 > tracing_on
> > +	   sleep 3
> > +	   echo c > /proc/sysrq-trigger
> > +
> > +	  After panic message, the kernel reboots and show test results
> > +	  on the boot log.
> 
>           After the panic message, the kernel will reboot and will show the
>           test results in the console output.
> 
> > +
> > +	  Note that user has to enable events on the persistent ring
> > +	  buffer manually to fill up ring buffers before rebooting.
> 
> 	  Note that events for the ring buffer needs to be enabled prior to
> 	  crashing the kernel so that the ring buffer has content that the
> 	  test will corrupt.
> 
> > +	  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.
> 
> 	  As the test will corrupt events in the "ptracingtest" persistent
> 	  ring buffer, it should not be used for any other purpose other
> 	  than his test.
> 
> 
> > +
> > +	  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 5ff632ca3858..fb098b0b4505 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -64,6 +64,10 @@ struct ring_buffer_cpu_meta {
> >  	unsigned long	commit_buffer;
> >  	__u32		subbuf_size;
> >  	__u32		nr_subbufs;
> > +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> > +	__u32		nr_invalid;
> > +	__u32		entry_bytes;
> > +#endif
> >  	int		buffers[];
> >  };
> >  
> > @@ -2079,6 +2083,21 @@ static void rb_meta_validate_events(struct
> > 	  ring_buffer_per_cpu *cpu_buffer) if (discarded)
> >  		pr_cont(" (%d pages discarded)", discarded);
> >  	pr_cont("\n");
> > +
> > +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> > +	if (meta->nr_invalid)
> > +		pr_warn("Ring buffer testing [%d] invalid pages: %s (%d/%d)\n",
> > +			cpu_buffer->cpu,
> > +			(discarded == meta->nr_invalid) ? "PASSED" : "FAILED",
> > +			discarded, meta->nr_invalid);
> > +	if (meta->entry_bytes)
> > +		pr_warn("Ring buffer testing [%d] entry_bytes: %s (%ld/%ld)\n",
> > +			cpu_buffer->cpu,
> > +			(entry_bytes == meta->entry_bytes) ? "PASSED" : "FAILED",
> > +			(long)entry_bytes, (long)meta->entry_bytes);
> > +	meta->nr_invalid = 0;
> > +	meta->entry_bytes = 0;
> > +#endif
> >  	return;
> >  
> >   invalid:
> > @@ -2559,12 +2578,67 @@ static void rb_free_cpu_buffer(struct
> > 	  ring_buffer_per_cpu *cpu_buffer) kfree(cpu_buffer);
> >  }
> >  
> > +#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
> > +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;
> > +	u32 entry_bytes = 0;
> > +	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;
> > +
> > +	for (i = 0; i < meta->nr_subbufs; i++) {
> > +		int idx = meta->buffers[i];
> > +
> > +		dpage = (void *)(ptr + idx * subbuf_size);
> > +		/* Skip unused pages */
> > +		if (!local_read(&dpage->commit))
> > +			continue;
> > +
> > +		/*
> > +		 * Invalidate even pages or multiples of 5. This will lead 3
> 
> 							    This will cause 3

OK, thanks for your comments. I'll update it according your
review.

Thank you,

> 
> -- Steve
> 
> > +		 * contiguous invalidated(empty) pages.
> > +		 */
> > +		if (!(i & 0x1) || !(i % 5)) {
> > +			local_add(subbuf_size + 1, &dpage->commit);
> > +			invalid++;
> > +		} else {
> > +			/* Count total commit bytes. */
> > +			entry_bytes += local_read(&dpage->commit);
> > +		}
> > +	}
> > +
> > +	pr_info("Inject invalidated %d pages on CPU%d, total size: %ld\n",
> > +		invalid, cpu, (long)entry_bytes);
> > +	meta->nr_invalid = invalid;
> > +	meta->entry_bytes = entry_bytes;
> > +}


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