Messages in this thread | | | Subject | Re: [PATCH v2] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line | From | Yang Jihong <> | Date | Mon, 21 Nov 2022 16:19:09 +0800 |
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Hello,
On 2022/11/21 3:38, Steven Rostedt wrote: > On Fri, 18 Nov 2022 18:25:21 +0800 > Yang Jihong <yangjihong1@huawei.com> wrote: > >> 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@huawei.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)) { > > We need to only do this if save_len is zero. Because the reason that it > returns TRACE_TYPE_PARTIAL_LINE is usually because it overflowed. > > This loops until the trace_seq is full, so it's OK to have it overflow. > The case I believe you are fixing, is the case were one > print_trace_line() actually fills the entire trace_seq in one shot. In > which case, it will never print, and in that case, save_len will be zero. > Yes, I'm fixing the situation you mentioned. For the sake of discussion, I've replied in the v1 patch to see if it's just add "trace_seq_puts(&iter->seq, "[LINE TOO BIG]\n");" or a more complex situation.
Thanks, Yang
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