From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The kernel command line ftrace_boot_snapshot by itself is supposed to
trigger a snapshot at the end of boot up of the main top level trace
buffer. A ftrace_boot_snapshot=foo will do the same for an instance called
foo that was created by trace_instance=foo,...

The logic was broken where if ftrace_boot_snapshot was by itself, it would
trigger a snapshot for all instances that had tracing enabled, regardless
if it asked for a snapshot or not.

When a snapshot is requested for a buffer, the buffer's
tr->allocated_snapshot is set to true. Use that to know if a trace buffer
wants a snapshot at boot up or not.

Since the top level buffer is part of the ftrace_trace_arrays list,
there's no reason to treat it differently than the other buffers. Just
iterate the list if ftrace_boot_snapshot was specified.

Cc: stable@vger.kernel.org
Fixes: 9c1c251d670bc ("tracing: Allow boot instances to have snapshot buffers")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ed1d1093f5e9..8ae51f1dea8e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10395,16 +10395,15 @@ void __init ftrace_boot_snapshot(void)
 {
 	struct trace_array *tr;
 
-	if (snapshot_at_boot) {
-		tracing_snapshot();
-		internal_trace_puts("** Boot snapshot taken **\n");
-	}
+	if (!snapshot_at_boot)
+		return;
 
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
-		if (tr == &global_trace)
+		if (!tr->allocated_snapshot)
 			continue;
-		trace_array_puts(tr, "** Boot snapshot taken **\n");
+
 		tracing_snapshot_instance(tr);
+		trace_array_puts(tr, "** Boot snapshot taken **\n");
 	}
 }
 
-- 
2.39.2

Hi Steven,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v6.3-rc5 next-20230404]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Steven-Rostedt/tracing-Have-tracing_snapshot_instance_cond-write-errors-to-the-appropriate-instance/20230405-070406
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20230404230308.501833715%40goodmis.org
patch subject: [PATCH 2/2] tracing: Fix ftrace_boot_snapshot command line logic
config: arc-buildonly-randconfig-r003-20230403 (https://download.01.org/0day-ci/archive/20230405/202304051001.dL3Fvaxd-lkp@intel.com/config)
compiler: arceb-elf-gcc (GCC) 12.1.0
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/intel-lab-lkp/linux/commit/ac5e916ec8d65b5e0c13719694efd3084105f416
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Steven-Rostedt/tracing-Have-tracing_snapshot_instance_cond-write-errors-to-the-appropriate-instance/20230405-070406
        git checkout ac5e916ec8d65b5e0c13719694efd3084105f416
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304051001.dL3Fvaxd-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/trace/trace.c: In function 'ftrace_boot_snapshot':
>> kernel/trace/trace.c:10402:24: error: 'struct trace_array' has no member named 'allocated_snapshot'
   10402 |                 if (!tr->allocated_snapshot)
         |                        ^~


vim +10402 kernel/trace/trace.c

 10393	
 10394	void __init ftrace_boot_snapshot(void)
 10395	{
 10396		struct trace_array *tr;
 10397	
 10398		if (!snapshot_at_boot)
 10399			return;
 10400	
 10401		list_for_each_entry(tr, &ftrace_trace_arrays, list) {
 10402			if (!tr->allocated_snapshot)
 10403				continue;
 10404	
 10405			tracing_snapshot_instance(tr);
 10406			trace_array_puts(tr, "** Boot snapshot taken **\n");
 10407		}
 10408	}
 10409	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests