Commit 6f42249f authored Mar 04, 2024 by Steven Rostedt (Google)

tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE

The trace_seq buffer is used to print out entire events. It's typically
set to PAGE_SIZE * 2 as there's some events that can be quite large.

As a side effect, writes to trace_marker is limited by both the size of the
trace_seq buffer as well as the ring buffer's sub-buffer size (which is a
power of PAGE_SIZE). By limiting the trace_seq size, it also limits the
size of the largest string written to trace_marker.

trace_seq does not need to be dependent on PAGE_SIZE like the ring buffer
sub-buffers need to be. Hard code it to 8K which is PAGE_SIZE * 2 on most
architectures. This will also limit the size of trace_marker on those
architectures with greater than 4K PAGE_SIZE.

Link: https://lore.kernel.org/all/20240302111244.3a1674be@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20240304191342.56fb1087@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

parent 5efd3e2a

include/linux/trace_seq.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -9,9 +9,15 @@
		/*
		* Trace sequences are used to allow a function to call several other functions
		* to create a string of data to use.
		*
		* Have the trace seq to be 8K which is typically PAGE_SIZE * 2 on
		* most architectures. The TRACE_SEQ_BUFFER_SIZE (which is
		* TRACE_SEQ_SIZE minus the other fields of trace_seq), is the
		* max size the output of a trace event may be.
		*/

		#define TRACE_SEQ_BUFFER_SIZE (PAGE_SIZE * 2 - \
		#define TRACE_SEQ_SIZE 8192
		#define TRACE_SEQ_BUFFER_SIZE (TRACE_SEQ_SIZE - \
		(sizeof(struct seq_buf) + sizeof(size_t) + sizeof(int)))

		struct trace_seq {