ring-buffer fixes for 7.1:

- Fix reporting MISSED EVENTS in trace iterator
 
   When the "trace" file is read with tracing enabled, if the writer
   were to pass the iterator reader, it resets, sets a "missed_events"
   flag and continues. The tracing output checks for missed events and
   if there are some, it prints out "[LOST EVENTS]" to let the user
   know events were dropped.
 
   But the clearing of the missed_events happened when the tracing system
   queried the ring buffer iterator about missed events. This was premature
   as the ring buffer is per CPU, and the tracing code reads all the
   CPU buffers and checks for missed events when it is read. If the
   CPU iterator that had missed events isn't printed next, the output
   for the LOST EVENTS is lost.
 
   Clear the missed_events flag when the iterator moves to the next event
   and not when the missed_events flag is queried. Also clear it on reset.
 
 - Flush and stop the persistent ring buffer on panic
 
   On panic the persistent ring buffer is used to debug what caused the
   panic. But on some architectures, it requires flushing the memory
   from cache, otherwise, the ring buffer persistent memory may not have
   the last events and this could also cause the ring buffer to be
   corrupted on the next boot.
 
 - Fix nr_subbufs initialization in simple_ring_buffer_init_mm
 
   The remote simple ring buffer  meta data nr_subbufs is initialized
   too early and gets cleared later on, making it zero and not reflect
   the actual number of sub-buffers.
 
 - Fix unload_page for simple_ring_buffer init rollback
 
   On error, the pages loaded need to be unloaded. To unload a page
   it is expected that: page = load_page(va); -> unload_page(page).
   But the code was doing: unload_page(va) and not unload_page(page).
 
 - Create output file from cmd_check_undefined
 
   The check for undefined symbols checks if the file *.o.checked exists
   and if so it skips doing the work. But the *.o.checked file never
   was created making every build do the work even when it was already
   done previously.
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Merge tag 'trace-ringbuffer-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ring-buffer fixes from Steven Rostedt:

 - Fix reporting MISSED EVENTS in trace iterator

   When the "trace" file is read with tracing enabled, if the writer
   were to pass the iterator reader, it resets, sets a "missed_events"
   flag and continues. The tracing output checks for missed events and
   if there are some, it prints out "[LOST EVENTS]" to let the user know
   events were dropped.

   But the clearing of the missed_events happened when the tracing
   system queried the ring buffer iterator about missed events. This was
   premature as the ring buffer is per CPU, and the tracing code reads
   all the CPU buffers and checks for missed events when it is read. If
   the CPU iterator that had missed events isn't printed next, the
   output for the LOST EVENTS is lost.

   Clear the missed_events flag when the iterator moves to the next
   event and not when the missed_events flag is queried. Also clear it
   on reset.

 - Flush and stop the persistent ring buffer on panic

   On panic the persistent ring buffer is used to debug what caused the
   panic. But on some architectures, it requires flushing the memory
   from cache, otherwise, the ring buffer persistent memory may not have
   the last events and this could also cause the ring buffer to be
   corrupted on the next boot.

 - Fix nr_subbufs initialization in simple_ring_buffer_init_mm

   The remote simple ring buffer meta data nr_subbufs is initialized too
   early and gets cleared later on, making it zero and not reflect the
   actual number of sub-buffers.

 - Fix unload_page for simple_ring_buffer init rollback

   On error, the pages loaded need to be unloaded. To unload a page it
   is expected that: page = load_page(va); -> unload_page(page). But the
   code was doing: unload_page(va) and not unload_page(page).

 - Create output file from cmd_check_undefined

   The check for undefined symbols checks if the file *.o.checked exists
   and if so it skips doing the work. But the *.o.checked file never was
   created making every build do the work even when it was already done
   previously.

* tag 'trace-ringbuffer-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing: Create output file from cmd_check_undefined
  tracing: Fix unload_page for simple_ring_buffer init rollback
  tracing: Fix nr_subbufs initialization in simple_ring_buffer_init_mm()
  ring-buffer: Flush and stop persistent ring buffer on panic
  ring-buffer: Fix reporting of missed events in iterator

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

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

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

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 */

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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__ */

kernel/trace/Makefile

@@ -154,7 +154,8 @@ quiet_cmd_check_undefined = NM      $<
               echo "Unexpected symbols in $<:" >&2; \
               echo "$$undefsyms" >&2; \
               false; \
-          fi
+          fi; \
+          touch $@
 
 $(obj)/%.o.checked: $(obj)/%.o $(obj)/undefsyms_base.o FORCE
 	$(call if_changed,check_undefined)

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;
 
@@ -2521,6 +2524,16 @@ 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,
@@ -2651,6 +2664,12 @@ 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:
@@ -2749,6 +2768,9 @@ 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);
@@ -5407,6 +5429,7 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
 	iter->head_page = cpu_buffer->reader_page;
 	iter->head = cpu_buffer->reader_page->read;
 	iter->next_event = iter->head;
+	iter->missed_events = 0;
 
 	iter->cache_reader_page = iter->head_page;
 	iter->cache_read = cpu_buffer->read;
@@ -6086,10 +6109,7 @@ ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
  */
 bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
 {
-	bool ret = iter->missed_events != 0;
-
-	iter->missed_events = 0;
-	return ret;
+	return iter->missed_events != 0;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
 
@@ -6251,7 +6271,7 @@ void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
-
+	iter->missed_events = 0;
 	rb_advance_iter(iter);
 
 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

kernel/trace/simple_ring_buffer.c

@@ -395,7 +395,6 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer,
 
 	memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta));
 	cpu_buffer->meta->meta_page_size = PAGE_SIZE;
-	cpu_buffer->meta->nr_subbufs = cpu_buffer->nr_pages;
 
 	/* The reader page is not part of the ring initially */
 	page = load_page(desc->page_va[0]);
@@ -431,12 +430,13 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer,
 
 	if (ret) {
 		for (i--; i >= 0; i--)
-			unload_page((void *)desc->page_va[i]);
+			unload_page(bpages[i].page);
 		unload_page(cpu_buffer->meta);
 
 		return ret;
 	}
 
+	cpu_buffer->meta->nr_subbufs = cpu_buffer->nr_pages;
 	/* Close the ring */
 	bpage->link.next = &cpu_buffer->tail_page->link;
 	cpu_buffer->tail_page->link.prev = &bpage->link;