Commit 40fc60e3 authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

trace_seq: Increase the buffer size to almost two pages 

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.

Link: https://lore.kernel.org/linux-trace-kernel/20231209175220.19867af4@gandalf.local.home



Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 8ec90be7

include/linux/trace_seq.h

+6 −3
Original line number Diff line number Diff line
@@ -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;

}

kernel/trace/trace.c

+3 −3
Original line number Diff line number Diff line
@@ -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 */
@@ -6932,8 +6932,8 @@ 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);

kernel/trace/trace_seq.c

+0 −3
Original line number Diff line number Diff line
@@ -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