[for-next,04/10] trace_seq: Increase the buffer size to almost two pages
Commit Message
From: "Steven Rostedt (Google)" <rostedt@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.
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>
---
include/linux/trace_seq.h | 9 ++++++---
kernel/trace/trace.c | 6 +++---
kernel/trace/trace_seq.c | 3 ---
3 files changed, 9 insertions(+), 9 deletions(-)
@@ -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;
}
@@ -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);
@@ -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