diff mbox series

tracing: Add snapshot at end of kernel boot up

Message ID 20220310214133.0e58e321@gandalf.local.home
State New
Headers show
Series tracing: Add snapshot at end of kernel boot up | expand

Commit Message

Steven Rostedt March 11, 2022, 2:41 a.m. UTC 
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Add ftrace_boot_snapshot kernel parameter that will take a snapshot at the
end of boot up just before switching over to user space (it happens during
the kernel freeing of init memory).

This is useful when there's interesting data that can be collected from
kernel start up, but gets overridden by user space start up code. With
this option, the ring buffer content from the boot up traces gets saved in
the snapshot at the end of boot up. This trace can be read from:

 /sys/kernel/tracing/snapshot

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 .../admin-guide/kernel-parameters.txt          |  8 ++++++++
 include/linux/ftrace.h                         | 11 ++++++++++-
 kernel/trace/ftrace.c                          |  2 ++
 kernel/trace/trace.c                           | 18 ++++++++++++++++++
 4 files changed, 38 insertions(+), 1 deletion(-)

Comments

kernel test robot March 11, 2022, 4:27 p.m. UTC | #1 
Hi Steven,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on rostedt-trace/for-next]
[also build test WARNING on linux/master hnaz-mm/master linus/master v5.17-rc7 next-20220310]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Steven-Rostedt/tracing-Add-snapshot-at-end-of-kernel-boot-up/20220311-104216
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next
config: x86_64-randconfig-a001 (https://download.01.org/0day-ci/archive/20220312/202203120019.Oteoj0K7-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 276ca87382b8f16a65bddac700202924228982f6)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/60ed6397c93a264f9ccbc8a6ca0b3ecc4dfdf6da
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Steven-Rostedt/tracing-Add-snapshot-at-end-of-kernel-boot-up/20220311-104216
        git checkout 60ed6397c93a264f9ccbc8a6ca0b3ecc4dfdf6da
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> WARNING: modpost: vmlinux.o(.text+0x179120): Section mismatch in reference from the function do_init_module() to the function .init.text:ftrace_boot_snapshot()
The function do_init_module() references
the function __init ftrace_boot_snapshot().
This is often because do_init_module lacks a __init
annotation or the annotation of ftrace_boot_snapshot is wrong.

---
0-DAY CI Kernel Test Service
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
diff mbox series

Patch

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f5a27f067db9..f6b7ee64ace8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1435,6 +1435,14 @@ 
 			as early as possible in order to facilitate early
 			boot debugging.
 
+	ftrace_boot_snapshot
+			[FTRACE] On boot up, a snapshot will be taken of the
+			ftrace ring buffer that can be read at:
+			/sys/kernel/tracing/snapshot.
+			This is useful if you need tracing information from kernel
+			boot up that is likely to be overridden by user space
+			start up functionality.
+
 	ftrace_dump_on_oops[=orig_cpu]
 			[FTRACE] will dump the trace buffers on oops.
 			If no parameter is passed, ftrace will dump
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 9999e29187de..ee91400c1c97 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -30,6 +30,12 @@ 
 #define ARCH_SUPPORTS_FTRACE_OPS 0
 #endif
 
+#ifdef CONFIG_TRACING
+extern void ftrace_boot_snapshot(void);
+#else
+static inline void ftrace_boot_snapshot(void) { }
+#endif
+
 #ifdef CONFIG_FUNCTION_TRACER
 struct ftrace_ops;
 struct ftrace_regs;
@@ -216,7 +222,10 @@  void ftrace_free_init_mem(void);
 void ftrace_free_mem(struct module *mod, void *start, void *end);
 #else
 static inline void ftrace_free_init_mem(void) { }
-static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
+static inline void ftrace_free_mem(struct module *mod, void *start, void *end)
+{
+	ftrace_boot_snapshot();
+}
 #endif
 
 /*
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7f93577ee428..9774ea0ad878 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7123,6 +7123,8 @@  void __init ftrace_free_init_mem(void)
 	void *start = (void *)(&__init_begin);
 	void *end = (void *)(&__init_end);
 
+	ftrace_boot_snapshot();
+
 	ftrace_free_mem(NULL, start, end);
 }
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7c85ce9ffdc3..eaf7d30ca6f1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -185,6 +185,7 @@  static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
 static char *default_bootup_tracer;
 
 static bool allocate_snapshot;
+static bool snapshot_at_boot;
 
 static int __init set_cmdline_ftrace(char *str)
 {
@@ -230,6 +231,15 @@  static int __init boot_alloc_snapshot(char *str)
 __setup("alloc_snapshot", boot_alloc_snapshot);
 
 
+static int __init boot_snapshot(char *str)
+{
+	snapshot_at_boot = true;
+	boot_alloc_snapshot(str);
+	return 1;
+}
+__setup("ftrace_boot_snapshot", boot_snapshot);
+
+
 static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
 
 static int __init set_trace_boot_options(char *str)
@@ -10149,6 +10159,14 @@  __init static int tracer_alloc_buffers(void)
 	return ret;
 }
 
+void __init ftrace_boot_snapshot(void)
+{
+	if (snapshot_at_boot) {
+		tracing_snapshot();
+		internal_trace_puts("** Boot snapshot taken **\n");
+	}
+}
+
 void __init early_trace_init(void)
 {
 	if (tracepoint_printk) {