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tracing: Add snapshot at end of kernel boot up

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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>
This commit is contained in:
Steven Rostedt (Google) 2022-03-10 21:37:09 -05:00
parent b3bc8547d3
commit 380af29b8d
4 changed files with 38 additions and 1 deletions
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8
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

11
include/linux/ftrace.h
View File

@ -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;
@ -215,7 +221,10 @@ struct ftrace_ops_hash {
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_init_mem(void)
{
ftrace_boot_snapshot();
}
static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
#endif

2
kernel/trace/ftrace.c
View File

@ -7096,6 +7096,8 @@ 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);
}

18
kernel/trace/trace.c
View File

@ -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 @@ out:
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) {