On Sat, 9 Dec 2023 17:52:20 -0500
Steven Rostedt <rost...@goodmis.org> wrote:
> From: "Steven Rostedt (Google)" <rost...@goodmis.org>
>
> Now that trace_marker can hold more than 1KB string, and can write as much
> as the ring buffer can hold, the trace_seq is not big enough to hold
> writes:
>
> ~# a="1234567890"
> ~# cnt=4080
> ~# s=""
> ~# while [ $cnt -gt 10 ]; do
> ~# s="${s}${a}"
> ~# cnt=$((cnt-10))
> ~# done
> ~# echo $s > trace_marker
> ~# cat trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 2/2 #P:8
> #
> # _-----=> irqs-off/BH-disabled
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # | | | ||||| | |
> <...>-860 [002] ..... 105.543465: tracing_mark_write[LINE
> TOO BIG]
> <...>-860 [002] ..... 105.543496: tracing_mark_write:
> 789012345678901234567890
>
> By increasing the trace_seq buffer to almost two pages, it can now print
> out the first line.
>
> This also subtracts the rest of the trace_seq fields from the buffer, so
> that the entire trace_seq is now PAGE_SIZE aligned.
Ok, but I just a bit concern about the memory consumption.
Since this is very specific case, can we make it configurable later?
Reviewed-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
Thanks,
>
> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
> ---
> include/linux/trace_seq.h | 9 ++++++---
> kernel/trace/trace.c | 6 +++---
> kernel/trace/trace_seq.c | 3 ---
> 3 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
> index 3691e0e76a1a..9ec229dfddaa 100644
> --- a/include/linux/trace_seq.h
> +++ b/include/linux/trace_seq.h
> @@ -8,11 +8,14 @@
>
> /*
> * Trace sequences are used to allow a function to call several other
> functions
> - * to create a string of data to use (up to a max of PAGE_SIZE).
> + * to create a string of data to use.
> */
>
> +#define TRACE_SEQ_BUFFER_SIZE (PAGE_SIZE * 2 - \
> + (sizeof(struct seq_buf) + sizeof(size_t) + sizeof(int)))
> +
> struct trace_seq {
> - char buffer[PAGE_SIZE];
> + char buffer[TRACE_SEQ_BUFFER_SIZE];
> struct seq_buf seq;
> size_t readpos;
> int full;
> @@ -21,7 +24,7 @@ struct trace_seq {
> static inline void
> trace_seq_init(struct trace_seq *s)
> {
> - seq_buf_init(&s->seq, s->buffer, PAGE_SIZE);
> + seq_buf_init(&s->seq, s->buffer, TRACE_SEQ_BUFFER_SIZE);
> s->full = 0;
> s->readpos = 0;
> }
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 83393c65ec71..da837119a446 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3753,7 +3753,7 @@ static bool trace_safe_str(struct trace_iterator *iter,
> const char *str,
>
> /* OK if part of the temp seq buffer */
> if ((addr >= (unsigned long)iter->tmp_seq.buffer) &&
> - (addr < (unsigned long)iter->tmp_seq.buffer + PAGE_SIZE))
> + (addr < (unsigned long)iter->tmp_seq.buffer +
> TRACE_SEQ_BUFFER_SIZE))
> return true;
>
> /* Core rodata can not be freed */
> @@ -6926,8 +6926,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
> goto out;
> }
>
> - if (cnt >= PAGE_SIZE)
> - cnt = PAGE_SIZE - 1;
> + if (cnt >= TRACE_SEQ_BUFFER_SIZE)
> + cnt = TRACE_SEQ_BUFFER_SIZE - 1;
>
> /* reset all but tr, trace, and overruns */
> trace_iterator_reset(iter);
> diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
> index 7be97229ddf8..c158d65a8a88 100644
> --- a/kernel/trace/trace_seq.c
> +++ b/kernel/trace/trace_seq.c
> @@ -13,9 +13,6 @@
> * trace_seq_init() more than once to reset the trace_seq to start
> * from scratch.
> *
> - * The buffer size is currently PAGE_SIZE, although it may become dynamic
> - * in the future.
> - *
> * A write to the buffer will either succeed or fail. That is, unlike
> * sprintf() there will not be a partial write (well it may write into
> * the buffer but it wont update the pointers). This allows users to
> --
> 2.42.0
>
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
