[PATCH 5.19 146/717] tracing: Wake up ring buffer waiters on closing of the file

Greg Kroah-Hartman
2022-10-22T07:43:40Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit f3ddb74ad0790030c9592229fb14d8c451f4e9a8 upstream.

When the file that represents the ring buffer is closed, there may be
waiters waiting on more input from the ring buffer. Call
ring_buffer_wake_waiters() to wake up any waiters when the file is
closed.

Link: https://lkml.kernel.org/r/20220927231825.182416969@goodmis.org

Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/trace_events.h | 1 +
kernel/trace/trace.c | 15 +++++++++++++++
2 files changed, 16 insertions(+)

--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -92,6 +92,7 @@ struct trace_iterator {
unsigned int temp_size;
char *fmt; /* modified format holder */
unsigned int fmt_size;
+ long wait_index;

/* trace_seq for __print_flags() and __print_symbolic() etc. */
struct trace_seq tmp_seq;
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8160,6 +8160,12 @@ static int tracing_buffers_release(struc

__trace_array_put(iter->tr);

+ iter->wait_index++;
+ /* Make sure the waiters see the new wait_index */
+ smp_wmb();
+
+ ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
+
if (info->spare)
ring_buffer_free_read_page(iter->array_buffer->buffer,
info->spare_cpu, info->spare);
@@ -8313,6 +8319,8 @@ tracing_buffers_splice_read(struct file

/* did we read anything? */
if (!spd.nr_pages) {
+ long wait_index;
+
if (ret)
goto out;

@@ -8320,10 +8328,17 @@ tracing_buffers_splice_read(struct file
if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
goto out;

+ wait_index = READ_ONCE(iter->wait_index);
+
ret = wait_on_pipe(iter, iter->tr->buffer_percent);
if (ret)
goto out;

+ /* Make sure we see the new wait_index */
+ smp_rmb();
+ if (wait_index != iter->wait_index)
+ goto out;
+
goto again;
}