The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x 49aa8a1f4d6800721c7971ed383078257f12e8f9 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024090835-matchbox-untreated-40ad@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

49aa8a1f4d68 ("tracing: Avoid possible softlockup in tracing_iter_reset()") bc1a72afdc4a ("ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 49aa8a1f4d6800721c7971ed383078257f12e8f9 Mon Sep 17 00:00:00 2001 From: Zheng Yejian zhengyejian@huaweicloud.com Date: Tue, 27 Aug 2024 20:46:54 +0800 Subject: [PATCH] tracing: Avoid possible softlockup in tracing_iter_reset()

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.

Cc: stable@vger.kernel.org Fixes: 2f26ebd549b9a ("tracing: use timestamp to determine start of latency traces") Link: https://lore.kernel.org/20240827124654.3817443-1-zhengyejian@huaweicloud.com Suggested-by: Steven Rostedt rostedt@goodmis.org Signed-off-by: Zheng Yejian zhengyejian@huaweicloud.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ebe7ce2f5f4a..edf6bc817aa1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3958,6 +3958,8 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu) break; entries++; ring_buffer_iter_advance(buf_iter); + /* This could be a big loop */ + cond_resched(); }

per_cpu_ptr(iter->array_buffer->data, cpu)->skipped_entries = entries;