Merge tag 'trace-v6.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing fixes from Steven Rostedt:

 - Fix sample code that uses trace_array_printk()

   The sample code for in kernel use of trace_array (that creates an
   instance for use within the kernel) and shows how to use
   trace_array_printk() that writes into the created instance, used
   trace_printk_init_buffers(). But that function is used to initialize
   normal trace_printk() and produces the NOTICE banner which is not
   needed for use of trace_array_printk(). The function to initialize
   that is trace_array_init_printk() that takes the created trace array
   instance as a parameter.

   Update the sample code to reflect the proper usage.

 - Fix preemption count output for stacktrace event

   The tracing buffer shows the preempt count level when an event
   executes. Because writing the event itself disables preemption, this
   needs to be accounted for when recording. The stacktrace event did
   not account for this so the output of the stacktrace event showed
   preemption was disabled while the event that triggered the stacktrace
   shows preemption is enabled and this leads to confusion. Account for
   preemption being disabled for the stacktrace event.

   The same happened for stack traces triggered by function tracer.

 - Fix persistent ring buffer when trace_pipe is used

   The ring buffer swaps the reader page with the next page to read from
   the write buffer when trace_pipe is used. If there's only a page of
   data in the ring buffer, this swap will cause the "commit" pointer
   (last data written) to be on the reader page. If more data is written
   to the buffer, it is added to the reader page until it falls off back
   into the write buffer.

   If the system reboots and the commit pointer is still on the reader
   page, even if new data was written, the persistent buffer validator
   will miss finding the commit pointer because it only checks the write
   buffer and does not check the reader page. This causes the validator
   to fail the validation and clear the buffer, where the new data is
   lost.

   There was a check for this, but it checked the "head pointer", which
   was incorrect, because the "head pointer" always stays on the write
   buffer and is the next page to swap out for the reader page. Fix the
   logic to catch this case and allow the user to still read the data
   after reboot.

* tag 'trace-v6.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Fix persistent buffer when commit page is the reader page
  ftrace: Fix preemption accounting for stacktrace filter command
  ftrace: Fix preemption accounting for stacktrace trigger command
  tracing: samples: Initialize trace_array_printk() with the correct function

Author: torvalds

kernel/trace/ring_buffer.c

@@ -1887,10 +1887,12 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 
 	head_page = cpu_buffer->head_page;
 
-	/* If both the head and commit are on the reader_page then we are done. */
-	if (head_page == cpu_buffer->reader_page &&
-	    head_page == cpu_buffer->commit_page)
+	/* If the commit_buffer is the reader page, update the commit page */
+	if (meta->commit_buffer == (unsigned long)cpu_buffer->reader_page->page) {
+		cpu_buffer->commit_page = cpu_buffer->reader_page;
+		/* Nothing more to do, the only page is the reader page */
 		goto done;
+	}
 
 	/* Iterate until finding the commit page */
 	for (i = 0; i < meta->nr_subbufs + 1; i++, rb_inc_page(&head_page)) {

kernel/trace/trace_events_trigger.c

@@ -1560,7 +1560,7 @@ stacktrace_trigger(struct event_trigger_data *data,
 	struct trace_event_file *file = data->private_data;
 
 	if (file)
-		__trace_stack(file->tr, tracing_gen_ctx(), STACK_SKIP);
+		__trace_stack(file->tr, tracing_gen_ctx_dec(), STACK_SKIP);
 	else
 		trace_dump_stack(STACK_SKIP);
 }

kernel/trace/trace_functions.c

@@ -633,11 +633,7 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
 
 static __always_inline void trace_stack(struct trace_array *tr)
 {
-	unsigned int trace_ctx;
-
-	trace_ctx = tracing_gen_ctx();
-
-	__trace_stack(tr, trace_ctx, FTRACE_STACK_SKIP);
+	__trace_stack(tr, tracing_gen_ctx_dec(), FTRACE_STACK_SKIP);
 }
 
 static void

samples/ftrace/sample-trace-array.c

@@ -112,7 +112,7 @@ static int __init sample_trace_array_init(void)
 	/*
 	 * If context specific per-cpu buffers havent already been allocated.
 	 */
-	trace_printk_init_buffers();
+	trace_array_init_printk(tr);
 
 	simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
 	if (IS_ERR(simple_tsk)) {