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Message-ID: <20221118102521.62362-1-yangjihong1@huawei.com>
Date: Fri, 18 Nov 2022 18:25:21 +0800
From: Yang Jihong <yangjihong1@...wei.com>
To: <rostedt@...dmis.org>, <mhiramat@...nel.org>,
<linux-kernel@...r.kernel.org>
CC: <yangjihong1@...wei.com>
Subject: [PATCH v2] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line
print_trace_line may overflow seq_file buffer. If the event is not
consumed, the while loop keeps peeking this event, causing a infinite loop.
Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
---
Changes since v1:
- Print partial line to show the broken trace event when overflowed print_trace_line
kernel/trace/trace.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 47a44b055a1d..81c36dc80212 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6786,7 +6786,32 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
ret = print_trace_line(iter);
if (ret == TRACE_TYPE_PARTIAL_LINE) {
- /* don't print partial lines */
+ /*
+ * If one trace_line of the tracer overflows seq_file
+ * buffer, trace_seq_to_user returns -EBUSY.
+ * In this case, we need to consume, otherwise,
+ * while loop will peek this event next time,
+ * resulting in an infinite loop.
+ */
+ if (trace_seq_has_overflowed(&iter->seq)) {
+ /*
+ * Print the partial line,
+ * that way we can see the broken trace event.
+ */
+ char dots[] = "...\n";
+
+ iter->seq.full = 0;
+ if (seq_buf_buffer_left(&iter->seq.seq) < strlen(dots)) {
+ iter->seq.seq.len =
+ seq_buf_used(&iter->seq.seq) - strlen(dots);
+ }
+ trace_seq_puts(&iter->seq, dots);
+
+ trace_consume(iter);
+ break;
+ }
+
+ /* In other cases, don't print partial lines */
iter->seq.seq.len = save_len;
break;
}
--
2.30.GIT
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