On Sat, 24 Aug 2024 11:03:43 +0800
Zheng Yejian <zhengyej...@huaweicloud.com> wrote:
> In __tracing_open(), when max latency tracers took place on the cpu,
> the time start of its buffer would be updated, then event entries with
> timestamps being earlier than start of the buffer would be skipped
> (see tracing_iter_reset()).
>
> Softlockup will occur if the kernel is non-preemptible and too many
> entries were skipped in the loop that reset every cpu buffer, so add
> cond_resched() to avoid it.
>
> Signed-off-by: Zheng Yejian <zhengyej...@huaweicloud.com>
> ---
> kernel/trace/trace.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ebe7ce2f5f4a..88faa95b457b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4706,6 +4706,15 @@ __tracing_open(struct inode *inode, struct file *file,
> bool snapshot)
> for_each_tracing_cpu(cpu) {
> ring_buffer_read_start(iter->buffer_iter[cpu]);
> tracing_iter_reset(iter, cpu);
> + /*
> + * When max latency tracers took place on the cpu, the
> time start
> + * of its buffer would be updated, then event entries
> with timestamps
> + * being earlier than start of the buffer would be
> skipped
> + * (see tracing_iter_reset()). Softlockup will occur if
> the kernel
> + * is non-preemptible and too many entries were skipped
> in the loop,
> + * so add cond_resched() to mitigate it.
> + */
> + cond_resched();
OK, but why we cond_resched() only here? Another tracing_iter_reset() in
s_start() does not cause the soft lockups in the same situation?
Thank you,
> }
> } else {
> cpu = iter->cpu_file;
> --
> 2.25.1
>
>
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
