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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: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2023-12-09 17:52:20 -05:00
parent 8ec90be7f1
commit 40fc60e36c
3 changed files with 9 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/trace_seq.h
View File

@ -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;
}

6
kernel/trace/trace.c
View File

@ -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 @@ waitagain:
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);

3
kernel/trace/trace_seq.c
View File

@ -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