On Tue, 24 Feb 2026 15:52:42 +0900 "Masami Hiramatsu (Google)" <[email protected]> wrote:
> From: Masami Hiramatsu (Google) <[email protected]> > > 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: [email protected] > Signed-off-by: Masami Hiramatsu (Google) <[email protected]> > --- > Changes in v3: > - update patch description. > --- > kernel/trace/ring_buffer.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index f16f053ef77d..3eb124c93d72 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> > @@ -589,6 +590,7 @@ 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 +2473,16 @@ static void rb_free_cpu_buffer(struct > ring_buffer_per_cpu *cpu_buffer) > kfree(cpu_buffer); > } > > +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_disable(buffer); I found this was a wrong API. I have to use ring_buffer_record_off(). > + flush_kernel_vmap_range((void *)buffer->range_addr_start, > + buffer->range_addr_end - > buffer->range_addr_start); This does nothing on arm64. Thanks, > + return NOTIFY_DONE; > +} > + > static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > int order, unsigned long start, > unsigned long end, > @@ -2590,6 +2602,12 @@ 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 +2695,9 @@ 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) <[email protected]>
