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Date: Tue, 16 Dec 2008 20:27:38 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] trace: add a way to enable or disable the stack tracer
On Tue, 16 Dec 2008 23:14:23 -0500 (EST) Steven Rostedt <rostedt@...dmis.org> wrote:
>
> The following patch is in:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
>
> branch: tip/devel
>
>
> Steven Rostedt (1):
> trace: add a way to enable or disable the stack tracer
>
> ----
> Documentation/kernel-parameters.txt | 4 +++
> include/linux/ftrace.h | 8 +++++
> kernel/sysctl.c | 10 +++++++
> kernel/trace/Kconfig | 13 ++++++---
> kernel/trace/trace_stack.c | 52 ++++++++++++++++++++++++++++++++---
> 5 files changed, 79 insertions(+), 8 deletions(-)
> ---------------------------
> commit ab8e30ab67495a48599edc11e805382da15b7761
> Author: Steven Rostedt <srostedt@...hat.com>
> Date: Tue Dec 16 23:06:40 2008 -0500
>
> trace: add a way to enable or disable the stack tracer
>
> Impact: enhancement to stack tracer
>
> The stack tracer currently is either on when configured in or
> off when it is not. It can not be disabled when it is configured on.
> (besides disabling the function tracer that it uses)
>
> This patch adds a way to enable or disable the stack tracer at
> run time. It defaults off on bootup, but a kernel parameter 'stacktrace'
> has been added to enable it on bootup.
>
> A new sysctl has been added "kernel.stack_tracer_enabled" to let
> the user enable or disable the stack tracer at run time.
>
Why do we need the boot parameter if there's a runtime control?
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 16aaa84..95fa674 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -89,6 +89,7 @@ parameter is applicable:
> SPARC Sparc architecture is enabled.
> SWSUSP Software suspend (hibernation) is enabled.
> SUSPEND System suspend states are enabled.
> + FTRACE Function tracing enabled.
> TS Appropriate touchscreen support is enabled.
> USB USB support is enabled.
> USBHID USB Human Interface Device support is enabled.
> @@ -2197,6 +2198,9 @@ and is between 256 and 4096 characters. It is defined in the file
> st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
> See Documentation/scsi/st.txt.
>
> + stacktrace [FTRACE]
> + Enabled the stack tracer on boot up.
> +
> sti= [PARISC,HW]
> Format: <num>
> Set the STI (builtin display/keyboard on the HP-PARISC
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 286af82..04b52e6 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -87,6 +87,14 @@ static inline void ftrace_stop(void) { }
> static inline void ftrace_start(void) { }
> #endif /* CONFIG_FUNCTION_TRACER */
>
> +#ifdef CONFIG_STACK_TRACER
> +extern int stack_tracer_enabled;
> +int
> +stack_trace_sysctl(struct ctl_table *table, int write,
> + struct file *file, void __user *buffer, size_t *lenp,
> + loff_t *ppos);
> +#endif
The ifdef could be omitted here.
> #ifdef CONFIG_DYNAMIC_FTRACE
> /* asm/ftrace.h must be defined for archs supporting dynamic ftrace */
> #include <asm/ftrace.h>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index c7bf3dd..2414fa8 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -488,6 +488,16 @@ static struct ctl_table kern_table[] = {
> .proc_handler = &ftrace_enable_sysctl,
> },
> #endif
> +#ifdef CONFIG_STACK_TRACER
> + {
> + .ctl_name = CTL_UNNUMBERED,
> + .procname = "stack_tracer_enabled",
> + .data = &stack_tracer_enabled,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = &stack_trace_sysctl,
> + },
> +#endif
> #ifdef CONFIG_TRACING
> {
> .ctl_name = CTL_UNNUMBERED,
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index d8bae6f..e2a4ff6 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -244,10 +244,15 @@ config STACK_TRACER
>
> This tracer works by hooking into every function call that the
> kernel executes, and keeping a maximum stack depth value and
> - stack-trace saved. Because this logic has to execute in every
> - kernel function, all the time, this option can slow down the
> - kernel measurably and is generally intended for kernel
> - developers only.
> + stack-trace saved. If this is configured with DYNAMIC_FTRACE
> + then it will not have any overhead while the stack tracer
> + is disabled.
> +
> + To enable the stack tracer on bootup, pass in 'stacktrace'
> + on the kernel command line.
> +
> + The stack tracer can also be enabled or disabled via the
> + sysctl kernel.stack_tracer_enabled
>
> Say N if unsure.
>
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 0b863f2..4842c96 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -10,6 +10,7 @@
> #include <linux/debugfs.h>
> #include <linux/ftrace.h>
> #include <linux/module.h>
> +#include <linux/sysctl.h>
> #include <linux/init.h>
> #include <linux/fs.h>
> #include "trace.h"
> @@ -31,6 +32,10 @@ static raw_spinlock_t max_stack_lock =
>
> static int stack_trace_disabled __read_mostly;
> static DEFINE_PER_CPU(int, trace_active);
> +static DEFINE_MUTEX(stack_sysctl_mutex);
> +
> +int stack_tracer_enabled;
> +static int last_stack_tracer_enabled;
>
> static inline void check_stack(void)
> {
> @@ -174,7 +179,7 @@ stack_max_size_write(struct file *filp, const char __user *ubuf,
> return count;
> }
>
> -static struct file_operations stack_max_size_fops = {
> +static const struct file_operations stack_max_size_fops = {
> .open = tracing_open_generic,
> .read = stack_max_size_read,
> .write = stack_max_size_write,
> @@ -272,7 +277,7 @@ static int t_show(struct seq_file *m, void *v)
> return 0;
> }
>
> -static struct seq_operations stack_trace_seq_ops = {
> +static const struct seq_operations stack_trace_seq_ops = {
> .start = t_start,
> .next = t_next,
> .stop = t_stop,
> @@ -288,12 +293,48 @@ static int stack_trace_open(struct inode *inode, struct file *file)
> return ret;
> }
>
> -static struct file_operations stack_trace_fops = {
> +static const struct file_operations stack_trace_fops = {
> .open = stack_trace_open,
> .read = seq_read,
> .llseek = seq_lseek,
> };
>
> +int
> +stack_trace_sysctl(struct ctl_table *table, int write,
> + struct file *file, void __user *buffer, size_t *lenp,
> + loff_t *ppos)
> +{
> + int ret;
> +
> + mutex_lock(&stack_sysctl_mutex);
> +
> + ret = proc_dointvec(table, write, file, buffer, lenp, ppos);
funny whitespace
> + if (ret || !write ||
> + (last_stack_tracer_enabled == stack_tracer_enabled))
> + goto out;
> +
> + last_stack_tracer_enabled = stack_tracer_enabled;
> +
> + if (stack_tracer_enabled)
> + register_ftrace_function(&trace_ops);
> + else
> + unregister_ftrace_function(&trace_ops);
> +
> + out:
> + mutex_unlock(&stack_sysctl_mutex);
> + return ret;
> +}
> +
> +static int start_stack_trace __initdata;
> +
> +static __init int enable_stacktrace(char *str)
> +{
> + start_stack_trace = 1;
> + return 1;
> +}
> +__setup("stacktrace", enable_stacktrace);
> +
> static __init int stack_trace_init(void)
> {
> struct dentry *d_tracer;
> @@ -311,7 +352,10 @@ static __init int stack_trace_init(void)
> if (!entry)
> pr_warning("Could not create debugfs 'stack_trace' entry\n");
>
> - register_ftrace_function(&trace_ops);
> + if (start_stack_trace) {
> + register_ftrace_function(&trace_ops);
> + stack_tracer_enabled = 1;
> + }
I think we could do away with start_stack_trace and just set
stack_tracer_enabled=1 in enable_stacktrace()?
--
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