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

If a process is waiting on the ring buffer for data, there currently isn't a clean way to force it to wake up. Add an ioctl call that will force any tasks that are waiting on the trace_pipe_raw file to wake up.

Link: https://lkml.kernel.org/r/20220929095029.117f913f@gandalf.local.home

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 --- kernel/trace/trace.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index e101b0764b39..58afc83afc9d 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8349,12 +8349,34 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, return ret; }

+/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */ +static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +{ + struct ftrace_buffer_info *info = file->private_data; + struct trace_iterator *iter = &info->iter; + + if (cmd) + return -ENOIOCTLCMD; + + mutex_lock(&trace_types_lock); + + 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); + + mutex_unlock(&trace_types_lock); + return 0; +} + static const struct file_operations tracing_buffers_fops = { .open = tracing_buffers_open, .read = tracing_buffers_read, .poll = tracing_buffers_poll, .release = tracing_buffers_release, .splice_read = tracing_buffers_splice_read, + .unlocked_ioctl = tracing_buffers_ioctl, .llseek = no_llseek, };