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[PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic

Masami Hiramatsu (Google) posted 4 patches 4 weeks ago
There is a newer version of this series
[PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Masami Hiramatsu (Google) 4 weeks ago 
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 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..930d96571f23
--- /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 */
+#define arch_ring_buffer_flush_range(start, end)	flush_cache_vmap(start, end)
+
+#endif /* __ASM_GENERIC_RING_BUFFER_H__ */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 353a5aa1b612..9f4ee9e3803d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6,6 +6,7 @@
  */
 #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>
@@ -30,6 +31,7 @@
 #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>
@@ -589,6 +591,7 @@ struct trace_buffer {
 
 	unsigned long			range_addr_start;
 	unsigned long			range_addr_end;
+	struct notifier_block		flush_nb;
 
 	struct ring_buffer_meta		*meta;
 
@@ -2471,6 +2474,16 @@ 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,
@@ -2590,6 +2603,12 @@ 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:
@@ -2677,6 +2696,9 @@ 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);
Re: [PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Masami Hiramatsu (Google) 2 weeks, 6 days ago 
On Wed, 11 Mar 2026 10:32:29 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> 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.

Hmm, on some architectures, flush_cache_vmap() is implemented using
on_each_cpu() which waits IPI. But that does not safe in panic notifier
because it is called after smp_send_stop().

Since this cache flush issue is currently only confirmed on arm64,
I would like to make it doing nothing (do { } while (0)) by default.

Thanks,

> 
> 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 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..930d96571f23
> --- /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 */
> +#define arch_ring_buffer_flush_range(start, end)	flush_cache_vmap(start, end)
> +
> +#endif /* __ASM_GENERIC_RING_BUFFER_H__ */
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 353a5aa1b612..9f4ee9e3803d 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -6,6 +6,7 @@
>   */
>  #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>
> @@ -30,6 +31,7 @@
>  #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>
> @@ -589,6 +591,7 @@ struct trace_buffer {
>  
>  	unsigned long			range_addr_start;
>  	unsigned long			range_addr_end;
> +	struct notifier_block		flush_nb;
>  
>  	struct ring_buffer_meta		*meta;
>  
> @@ -2471,6 +2474,16 @@ 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,
> @@ -2590,6 +2603,12 @@ 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:
> @@ -2677,6 +2696,9 @@ 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);
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Re: [PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Mathieu Desnoyers 2 weeks, 6 days ago 
On 2026-03-18 10:19, Masami Hiramatsu (Google) wrote:
> On Wed, 11 Mar 2026 10:32:29 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> 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.
> 
> Hmm, on some architectures, flush_cache_vmap() is implemented using
> on_each_cpu() which waits IPI. But that does not safe in panic notifier
> because it is called after smp_send_stop().
> 
> Since this cache flush issue is currently only confirmed on arm64,
> I would like to make it doing nothing (do { } while (0)) by default.

FWIW, I've sent a related series a while ago about flushing pmem
areas to memory on panic:

https://lore.kernel.org/lkml/20240618154157.334602-3-mathieu.desnoyers@efficios.com/

When reading your patch, I feel like I'm missing something, so please bear with
me for a few questions:

- What exactly are you trying to flush ? By "flush" do you mean
   evince cache lines or write back cache lines ? (I expect you aim
   at the second option)

- AFAIU, you are not trying to evince cache lines after creation
   of a new virtual mapping (which is the documented intent of
   flush_cache_vmap).
   
- AFAIU flush_cache_vmap maps to no-code on arm64 (asm-generic), what am
   I missing ? It makes sense to be a no-op because AFAIR arm64 does not
   have to deal with virtually aliasing caches.

see commit 8690bbcf3b7 ("Introduce cpu_dcache_is_aliasing() across all architectures")

The arch_wb_cache_pmem is specific to pmem, which is not exactly what you want
to use, but on arm64 it's implemented as:

         /* Ensure order against any prior non-cacheable writes */
         dmb(osh);
         dcache_clean_pop((unsigned long)addr, (unsigned long)addr + size);

Which I think has the writeback semantic you are looking for, and AFAIU should no
require IPIs (at least on arm64) to flush cache lines across the entire system.

Cheers,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
Re: [PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Masami Hiramatsu (Google) 2 weeks, 6 days ago 
On Wed, 18 Mar 2026 10:53:26 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> On 2026-03-18 10:19, Masami Hiramatsu (Google) wrote:
> > On Wed, 11 Mar 2026 10:32:29 +0900
> > "Masami Hiramatsu (Google)" <mhiramat@kernel.org> 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.
> > 
> > Hmm, on some architectures, flush_cache_vmap() is implemented using
> > on_each_cpu() which waits IPI. But that does not safe in panic notifier
> > because it is called after smp_send_stop().
> > 
> > Since this cache flush issue is currently only confirmed on arm64,
> > I would like to make it doing nothing (do { } while (0)) by default.
> 
> FWIW, I've sent a related series a while ago about flushing pmem
> areas to memory on panic:
> 
> https://lore.kernel.org/lkml/20240618154157.334602-3-mathieu.desnoyers@efficios.com/
> 

Ah, nice!

> When reading your patch, I feel like I'm missing something, so please bear with
> me for a few questions:
> 
> - What exactly are you trying to flush ? By "flush" do you mean
>    evince cache lines or write back cache lines ? (I expect you aim
>    at the second option)

Yes, I need to write back cache lines, at least it can be
read after hot reboot. (not evict cache)

> 
> - AFAIU, you are not trying to evince cache lines after creation
>    of a new virtual mapping (which is the documented intent of
>    flush_cache_vmap).

Ah, OK. That's a good point!
(anyway I will replace it with do { } while (0) in the next version.)

>    
> - AFAIU flush_cache_vmap maps to no-code on arm64 (asm-generic), what am
>    I missing ? It makes sense to be a no-op because AFAIR arm64 does not
>    have to deal with virtually aliasing caches.

Yeah, so my patch also introduces arm64 specific implementation.

> 
> see commit 8690bbcf3b7 ("Introduce cpu_dcache_is_aliasing() across all architectures")

OK, let me check.

> 
> The arch_wb_cache_pmem is specific to pmem, which is not exactly what you want
> to use, but on arm64 it's implemented as:
> 
>          /* Ensure order against any prior non-cacheable writes */
>          dmb(osh);
>          dcache_clean_pop((unsigned long)addr, (unsigned long)addr + size);
> 
> Which I think has the writeback semantic you are looking for, and AFAIU should no
> require IPIs (at least on arm64) to flush cache lines across the entire system.

Yes, that's what I need.

Thank you!


> 
> Cheers,
> 
> Mathieu
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Re: [PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Mathieu Desnoyers 2 weeks, 6 days ago 
On 2026-03-18 11:29, Masami Hiramatsu (Google) wrote:
>>
>> - AFAIU, you are not trying to evince cache lines after creation
>>     of a new virtual mapping (which is the documented intent of
>>     flush_cache_vmap).
> 
> Ah, OK. That's a good point!
> (anyway I will replace it with do { } while (0) in the next version.)
> 
>>     
>> - AFAIU flush_cache_vmap maps to no-code on arm64 (asm-generic), what am
>>     I missing ? It makes sense to be a no-op because AFAIR arm64 does not
>>     have to deal with virtually aliasing caches.
> 
> Yeah, so my patch also introduces arm64 specific implementation.

Just make sure to call this something else than "flush_cache_vmap",
because you don't want to slow down vmap on arm64 which does not
require to evince and certainly not write back cache lines after
creation of a new virtual mapping.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
Re: [PATCH v9 2/4] ring-buffer: Flush and stop persistent ring buffer on panic
Posted by Masami Hiramatsu (Google) 2 weeks, 5 days ago 
On Wed, 18 Mar 2026 11:51:28 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> On 2026-03-18 11:29, Masami Hiramatsu (Google) wrote:
> >>
> >> - AFAIU, you are not trying to evince cache lines after creation
> >>     of a new virtual mapping (which is the documented intent of
> >>     flush_cache_vmap).
> > 
> > Ah, OK. That's a good point!
> > (anyway I will replace it with do { } while (0) in the next version.)
> > 
> >>     
> >> - AFAIU flush_cache_vmap maps to no-code on arm64 (asm-generic), what am
> >>     I missing ? It makes sense to be a no-op because AFAIR arm64 does not
> >>     have to deal with virtually aliasing caches.
> > 
> > Yeah, so my patch also introduces arm64 specific implementation.
> 
> Just make sure to call this something else than "flush_cache_vmap",
> because you don't want to slow down vmap on arm64 which does not
> require to evince and certainly not write back cache lines after
> creation of a new virtual mapping.

OK, I will just leave it an empty do-while in asm-generic instead of
flush_cache_vmap(). If any architecture finds persistent ring buffer
needs to write back caches, it can add its own flush implementation.

BTW, do we need dmb(osh)? This runs dcache_clean_pop() after atomic
operation in ring_buffer_record_off().

	ring_buffer_record_off(buffer);
	arch_ring_buffer_flush_range(buffer->range_addr_start, buffer->range_addr_end);

Thank you,

> 
> Thanks,
> 
> Mathieu
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com


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

Patchew 2.1-devel-ea86937

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