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    SubjectRe: [PATCH 3/5] ftrace: add ftrace_bprintk()
    From
    2009/3/2 Steven Rostedt <rostedt@goodmis.org>:
    >
    > On Sat, 28 Feb 2009, Frederic Weisbecker wrote:
    >
    >> From: Lai Jiangshan <laijs@cn.fujitsu.com>
    >>
    >> Impact: Add a generic printk() for ftrace, like ftrace_printk()
    >>
    >> ftrace_bprintk() use the infrastructure to record events on ring_buffer.
    >>
    >> [fweisbec@gmail.com: ported to latest -tip and made it work if !CONFIG_MODULES]
    >>
    >> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    >> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    >> ---
    >>  include/asm-generic/vmlinux.lds.h |    3 +
    >>  include/linux/ftrace.h            |   21 ++++++
    >>  include/linux/module.h            |    5 ++
    >>  kernel/module.c                   |    6 ++
    >>  kernel/trace/trace.c              |   15 ++++
    >>  kernel/trace/trace_bprintk.c      |  132 ++++++++++++++++++++++++++++++++++++-
    >>  6 files changed, 181 insertions(+), 1 deletions(-)
    >>
    >> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
    >> index 9d97491..13f20f4 100644
    >> --- a/include/asm-generic/vmlinux.lds.h
    >> +++ b/include/asm-generic/vmlinux.lds.h
    >> @@ -100,6 +100,9 @@
    >>               *(__vermagic)           /* Kernel version magic */      \
    >>               *(__markers_strings)    /* Markers: strings */          \
    >>               *(__tracepoints_strings)/* Tracepoints: strings */      \
    >> +             VMLINUX_SYMBOL(__start___trace_bprintk_fmt) = .;        \
    >> +             *(__trace_printk_fmt)   /* Trace_printk fmt' pointer */ \
    >> +             VMLINUX_SYMBOL(__stop___trace_bprintk_fmt) = .;         \
    >
    > If this can only be done when tracing is enabled, I would wrap that up
    > in a macro that is a nop when tracing is disabled.


    Ah, good catch.


    >>       }                                                               \
    >>                                                                       \
    >>       .rodata1          : AT(ADDR(.rodata1) - LOAD_OFFSET) {          \
    >> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
    >> index 8ac2fac..f82b986 100644
    >> --- a/include/linux/ftrace.h
    >> +++ b/include/linux/ftrace.h
    >> @@ -224,6 +224,27 @@ extern int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr);
    >>
    >>  #ifdef CONFIG_TRACE_BPRINTK
    >>  extern int trace_vbprintk(unsigned long ip, const char *fmt, va_list args);
    >> +extern int __ftrace_bprintk(unsigned long ip, const char *fmt, ...)
    >> +             __attribute__ ((format (printf, 2, 3)));
    >> +
    >> +static inline void  ____ftrace_bprintk_check_format(const char *fmt, ...)
    >> +             __attribute__ ((format (printf, 1, 2)));
    >> +static inline void ____ftrace_bprintk_check_format(const char *fmt, ...) {}
    >> +#define __ftrace_bprintk_check_format(fmt, args...)                  \
    >> +do {                                                                 \
    >> +     if (0)                                                          \
    >> +             ____ftrace_bprintk_check_format(fmt, ##args);           \
    >> +} while (0)
    >> +
    >> +#define ftrace_bprintk(fmt, args...)                                 \
    >> +do {                                                                 \
    >> +     static char *__attribute__((section("__trace_bprintk_fmt")))    \
    >> +                     ftrace_bprintk_fmt = fmt;                       \
    >> +     __ftrace_bprintk_check_format(fmt, ##args);                     \
    >> +     __ftrace_bprintk(_THIS_IP_, ftrace_bprintk_fmt, ##args);        \
    >> +} while (0)
    >> +#else
    >> +#define ftrace_bprintk ftrace_printk
    >>  #endif
    >>
    >>  /* May be defined in arch */
    >> diff --git a/include/linux/module.h b/include/linux/module.h
    >> index 07b1cb4..c4f2845 100644
    >> --- a/include/linux/module.h
    >> +++ b/include/linux/module.h
    >> @@ -347,6 +347,11 @@ struct module
    >>       unsigned int num_tracepoints;
    >>  #endif
    >>
    >> +#ifdef CONFIG_TRACE_BPRINTK
    >> +     const char **trace_bprintk_fmt_start;
    >> +     unsigned int num_trace_bprintk_fmt;
    >> +#endif
    >> +
    >>  #ifdef CONFIG_MODULE_UNLOAD
    >>       /* What modules depend on me? */
    >>       struct list_head modules_which_use_me;
    >> diff --git a/kernel/module.c b/kernel/module.c
    >> index 90a6d63..fa96909 100644
    >> --- a/kernel/module.c
    >> +++ b/kernel/module.c
    >> @@ -2192,6 +2192,12 @@ static noinline struct module *load_module(void __user *umod,
    >>                                       &mod->num_tracepoints);
    >>  #endif
    >>
    >> +#ifdef CONFIG_TRACE_BPRINTK
    >> +     mod->trace_bprintk_fmt_start = section_objs(hdr, sechdrs, secstrings,
    >> +                     "__trace_bprintk_fmt", sizeof(char *),
    >> +                     &mod->num_trace_bprintk_fmt);
    >> +#endif
    >> +
    >>  #ifdef CONFIG_MODVERSIONS
    >>       if ((mod->num_syms && !mod->crcs)
    >>           || (mod->num_gpl_syms && !mod->gpl_crcs)
    >> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    >> index 3a3ae19..0e30dce 100644
    >> --- a/kernel/trace/trace.c
    >> +++ b/kernel/trace/trace.c
    >> @@ -3627,6 +3627,21 @@ out:
    >>  }
    >>  EXPORT_SYMBOL_GPL(trace_vbprintk);
    >>
    >> +int __ftrace_bprintk(unsigned long ip, const char *fmt, ...)
    >> +{
    >> +     int ret;
    >> +     va_list ap;
    >> +
    >> +     if (!fmt)
    >> +             return 0;
    >> +
    >> +     va_start(ap, fmt);
    >> +     ret = trace_vbprintk(ip, fmt, ap);
    >> +     va_end(ap);
    >> +     return ret;
    >> +}
    >> +EXPORT_SYMBOL_GPL(__ftrace_bprintk);
    >> +
    >>  static int trace_panic_handler(struct notifier_block *this,
    >>                              unsigned long event, void *unused)
    >>  {
    >> diff --git a/kernel/trace/trace_bprintk.c b/kernel/trace/trace_bprintk.c
    >> index 1f8e532..28e6286 100644
    >> --- a/kernel/trace/trace_bprintk.c
    >> +++ b/kernel/trace/trace_bprintk.c
    >> @@ -19,9 +19,23 @@
    >>
    >>  #include "trace.h"
    >>
    >> +#ifdef CONFIG_MODULE> +
    >>  /* binary printk basic */
    >>  static DEFINE_MUTEX(btrace_mutex);
    >>  static int btrace_metadata_count;
    >> +/*
    >> + * modules ftrace_bprintk()'s formats are autosaved in struct trace_bprintk_fmt
    >> + * which are queued on trace_bprintk_fmt_list.
    >> + */
    >> +static LIST_HEAD(trace_bprintk_fmt_list);
    >> +
    >> +struct trace_bprintk_fmt {
    >> +     struct list_head list;
    >> +     int count;
    >> +     char fmt[0];
    >> +};
    >> +
    >>
    >>  static inline void lock_btrace(void)
    >>  {
    >> @@ -33,6 +47,93 @@ static inline void unlock_btrace(void)
    >>       mutex_unlock(&btrace_mutex);
    >>  }
    >>
    >> +/*
    >> + * If trace_bprintk() is not active, we release the trace_bprintk's
    >> + * formats that no modules has reference to.
    >> + */
    >> +static inline void shrink_trace_bprintk_fmt(void)
    >> +{
    >> +     struct trace_bprintk_fmt *pos, *next;
    >> +     list_for_each_entry_safe(pos, next, &trace_bprintk_fmt_list, list) {
    >> +             if (!pos->count) {
    >> +                     list_del(&pos->list);
    >> +                     kfree(pos);
    >> +             }
    >> +     }
    >> +}
    >> +
    >> +static inline struct trace_bprintk_fmt *lookup_format(const char *fmt)
    >> +{
    >> +     struct trace_bprintk_fmt *pos;
    >> +     list_for_each_entry(pos, &trace_bprintk_fmt_list, list) {
    >> +             if (!strcmp(pos->fmt, fmt))
    >> +                     return pos;
    >> +     }
    >> +     return NULL;
    >> +}
    >> +
    >> +static
    >> +void hold_module_trace_bprintk_format(const char **start, const char **end)
    >> +{
    >> +     const char **iter;
    >> +     lock_btrace();
    >> +     for (iter = start; iter < end; iter++) {
    >> +             struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);
    >> +             if (tb_fmt) {
    >> +                     tb_fmt->count++;
    >> +                     *iter = tb_fmt->fmt;
    >> +                     continue;
    >> +             }
    >> +
    >> +             tb_fmt = kmalloc(offsetof(struct trace_bprintk_fmt, fmt)
    >> +                             + strlen(*iter) + 1, GFP_KERNEL);
    >> +             if (tb_fmt) {
    >> +                     list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
    >> +                     tb_fmt->count = 1;
    >> +                     strcpy(tb_fmt->fmt, *iter);
    >> +                     *iter = tb_fmt->fmt;
    >> +             } else
    >> +                     *iter = NULL;
    >> +     }
    >> +     unlock_btrace();
    >> +}
    >> +
    >> +static
    >> +void release_module_trace_bprintk_format(const char **start, const char **end)
    >> +{
    >> +     const char **iter;
    >> +     lock_btrace();
    >> +     for (iter = start; iter < end; iter++) {
    >> +             struct trace_bprintk_fmt *tb_fmt;
    >> +             if (!*iter)
    >> +                     continue;
    >> +
    >> +             tb_fmt = container_of(*iter, struct trace_bprintk_fmt, fmt[0]);
    >> +             tb_fmt->count--;
    >> +             if (!tb_fmt->count && !btrace_metadata_count) {
    >> +                     list_del(&tb_fmt->list);
    >> +                     kfree(tb_fmt);
    >
    > Shouldn't *iter get assigned to NULL somewhere here?
    >
    > -- Steve


    Hm, why?

    >
    >> +             }
    >> +     }
    >> +     unlock_btrace();
    >> +}
    >> +
    >> +static int module_trace_bprintk_format_notify(struct notifier_block *self,
    >> +             unsigned long val, void *data)
    >> +{
    >> +     struct module *mod = data;
    >> +     if (mod->num_trace_bprintk_fmt) {
    >> +             const char **start = mod->trace_bprintk_fmt_start;
    >> +             const char **end = start + mod->num_trace_bprintk_fmt;
    >> +
    >> +             if (val == MODULE_STATE_COMING)
    >> +                     hold_module_trace_bprintk_format(start, end);
    >> +             else if (val == MODULE_STATE_GOING)
    >> +                     release_module_trace_bprintk_format(start, end);
    >> +     }
    >> +     return 0;
    >> +}
    >> +
    >>  static void get_btrace_metadata(void)
    >>  {
    >>       lock_btrace();
    >> @@ -44,9 +145,31 @@ static void put_btrace_metadata(void)
    >>  {
    >>       lock_btrace();
    >>       btrace_metadata_count--;
    >> +
    >> +     if (!btrace_metadata_count) {
    >> +             shrink_trace_bprintk_fmt();
    >> +     }
    >>       unlock_btrace();
    >>  }
    >>
    >> +#else /* !CONFIG_MODULES */
    >> +__init static int
    >> +module_trace_bprintk_format_notify(struct notifier_block *self,
    >> +             unsigned long val, void *data)
    >> +{
    >> +     return 0;
    >> +}
    >> +
    >> +static inline void get_btrace_metadata(void) { }
    >> +static inline void put_btrace_metadata(void) { }
    >> +#endif /* CONFIG_MODULES */
    >> +
    >> +
    >> +__initdata_or_module static
    >> +struct notifier_block module_trace_bprintk_format_nb = {
    >> +     .notifier_call = module_trace_bprintk_format_notify,
    >> +};
    >> +
    >>  /* events tracer */
    >>  int trace_bprintk_enable;
    >>
    >> @@ -81,7 +204,14 @@ static struct tracer bprintk_trace __read_mostly =
    >>
    >>  static __init int init_bprintk(void)
    >>  {
    >> -     return register_tracer(&bprintk_trace);
    >> +     int ret = register_module_notifier(&module_trace_bprintk_format_nb);
    >> +     if (ret)
    >> +             return ret;
    >> +
    >> +     ret = register_tracer(&bprintk_trace);
    >> +     if (ret)
    >> +             unregister_module_notifier(&module_trace_bprintk_format_nb);
    >> +     return ret;
    >>  }
    >>
    >>  device_initcall(init_bprintk);
    >> --
    >> 1.6.1
    >>
    >>
    >>
    >
    --
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