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>

diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index 3691e0e76a1a209601f97fe03ca97738dafcd841..9ec229dfddaa774b9c0a4f2ae410eb273061c330 100644 (file)
--- 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 dba1328e454b35f690e9fdd1be214fc7752cdac8..0be30cccabb4ba29098562eb35ba1783f87f8a98 100644 (file)
--- 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 */
@@ -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);

diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index 7be97229ddf86008a4fa91c4872f3b9eb85a5181..c158d65a8a886efc64516d7dd8a333aa27da594e 100644 (file)
--- 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