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Date: Mon, 24 Oct 2022 13:27:38 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, "Steven Rostedt (Google)" <rostedt@...dmis.org> Subject: [PATCH 5.15 114/530] tracing: Add ioctl() to force ring buffer waiters to wake up From: Steven Rostedt (Google) <rostedt@...dmis.org> commit 01b2a52171735c6eea80ee2f355f32bea6c41418 upstream. 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@...r.kernel.org Cc: Ingo Molnar <mingo@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org> Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice") Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- kernel/trace/trace.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8310,12 +8310,34 @@ out: 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, };
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