From: Steven Rostedt <rostedt@xxxxxxxxxxx> When running the following: # cd /sys/kernel/tracing/ # echo 1 > events/sched/sched_waking/enable # echo 1 > events/sched/sched_switch/enable # echo 0 > tracing_on # dd if=per_cpu/cpu0/trace_pipe_raw of=/tmp/raw0.dat The dd task would get stuck in an infinite loop in the kernel. What would happen is the following: When ring_buffer_read_page() returns -1 (no data) then a check is made to see if the buffer is empty (as happens when the page is not full), it will call wait_on_pipe() to wait until the ring buffer has data. When it is it will try again to read data (unless O_NONBLOCK is set). The issue happens when there's a reader and the file descriptor is closed. The wait_on_pipe() will return when that is the case. But this loop will continue to try again and wait_on_pipe() will again return immediately and the loop will continue and never stop. Simply check if the file was closed before looping and exit out if it is. Cc: stable@xxxxxxxxxxxxxxx Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Link: https://lore.kernel.org/20240808235730.78bf63e5@xxxxxxxxxxxxxxxxxxxx Fixes: 2aa043a55b9a7 ("tracing/ring-buffer: Fix wait_on_pipe() race") Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> --- kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 10cd38bce2f1..ebe7ce2f5f4a 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -7956,7 +7956,7 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, trace_access_unlock(iter->cpu_file); if (ret < 0) { - if (trace_empty(iter)) { + if (trace_empty(iter) && !iter->closed) { if ((filp->f_flags & O_NONBLOCK)) return -EAGAIN; -- 2.43.0
