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    Subject[PATCH 11/17] ftrace,kdb: Extend kdb to be able to dump the ftrace buffer
    Date
    Add in a helper function to allow the kdb shell to dump the ftrace
    buffer.

    Modify trace.c to expose the capability to iterate over the ftrace
    buffer in a read only capacity.

    Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    CC: Frederic Weisbecker <fweisbec@gmail.com>
    ---
    kernel/trace/Makefile | 3 +
    kernel/trace/trace.c | 43 +++++++++--------
    kernel/trace/trace.h | 19 +++++++
    kernel/trace/trace_kdb.c | 119 ++++++++++++++++++++++++++++++++++++++++++++++
    4 files changed, 163 insertions(+), 21 deletions(-)
    create mode 100644 kernel/trace/trace_kdb.c

    diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
    index ffb1a5b..4215530 100644
    --- a/kernel/trace/Makefile
    +++ b/kernel/trace/Makefile
    @@ -57,5 +57,8 @@ obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
    obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
    obj-$(CONFIG_KSYM_TRACER) += trace_ksym.o
    obj-$(CONFIG_EVENT_TRACING) += power-traces.o
    +ifeq ($(CONFIG_TRACING),y)
    +obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
    +endif

    libftrace-y := ftrace.o
    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 086d363..d6736b9 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -101,10 +101,7 @@ static inline void ftrace_enable_cpu(void)
    preempt_enable();
    }

    -static cpumask_var_t __read_mostly tracing_buffer_mask;
    -
    -#define for_each_tracing_cpu(cpu) \
    - for_each_cpu(cpu, tracing_buffer_mask)
    +cpumask_var_t __read_mostly tracing_buffer_mask;

    /*
    * ftrace_dump_on_oops - variable to dump ftrace buffer on oops
    @@ -1539,11 +1536,6 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
    }
    EXPORT_SYMBOL_GPL(trace_vprintk);

    -enum trace_file_type {
    - TRACE_FILE_LAT_FMT = 1,
    - TRACE_FILE_ANNOTATE = 2,
    -};
    -
    static void trace_iterator_increment(struct trace_iterator *iter)
    {
    /* Don't allow ftrace to trace into the ring buffers */
    @@ -1641,7 +1633,7 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
    }

    /* Find the next real entry, and increment the iterator to the next entry */
    -static void *find_next_entry_inc(struct trace_iterator *iter)
    +void *trace_find_next_entry_inc(struct trace_iterator *iter)
    {
    iter->ent = __find_next_entry(iter, &iter->cpu,
    &iter->lost_events, &iter->ts);
    @@ -1676,19 +1668,19 @@ static void *s_next(struct seq_file *m, void *v, loff_t *pos)
    return NULL;

    if (iter->idx < 0)
    - ent = find_next_entry_inc(iter);
    + ent = trace_find_next_entry_inc(iter);
    else
    ent = iter;

    while (ent && iter->idx < i)
    - ent = find_next_entry_inc(iter);
    + ent = trace_find_next_entry_inc(iter);

    iter->pos = *pos;

    return ent;
    }

    -static void tracing_iter_reset(struct trace_iterator *iter, int cpu)
    +void tracing_iter_reset(struct trace_iterator *iter, int cpu)
    {
    struct trace_array *tr = iter->tr;
    struct ring_buffer_event *event;
    @@ -2049,7 +2041,7 @@ int trace_empty(struct trace_iterator *iter)
    }

    /* Called with trace_event_read_lock() held. */
    -static enum print_line_t print_trace_line(struct trace_iterator *iter)
    +enum print_line_t print_trace_line(struct trace_iterator *iter)
    {
    enum print_line_t ret;

    @@ -3211,7 +3203,7 @@ waitagain:

    trace_event_read_lock();
    trace_access_lock(iter->cpu_file);
    - while (find_next_entry_inc(iter) != NULL) {
    + while (trace_find_next_entry_inc(iter) != NULL) {
    enum print_line_t ret;
    int len = iter->seq.len;

    @@ -3294,7 +3286,7 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
    if (ret != TRACE_TYPE_NO_CONSUME)
    trace_consume(iter);
    rem -= count;
    - if (!find_next_entry_inc(iter)) {
    + if (!trace_find_next_entry_inc(iter)) {
    rem = 0;
    iter->ent = NULL;
    break;
    @@ -3350,7 +3342,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
    if (ret <= 0)
    goto out_err;

    - if (!iter->ent && !find_next_entry_inc(iter)) {
    + if (!iter->ent && !trace_find_next_entry_inc(iter)) {
    ret = -EFAULT;
    goto out_err;
    }
    @@ -4414,7 +4406,7 @@ static struct notifier_block trace_die_notifier = {
    */
    #define KERN_TRACE KERN_EMERG

    -static void
    +void
    trace_printk_seq(struct trace_seq *s)
    {
    /* Probably should print a warning here. */
    @@ -4429,6 +4421,13 @@ trace_printk_seq(struct trace_seq *s)
    trace_seq_init(s);
    }

    +void trace_init_global_iter(struct trace_iterator *iter)
    +{
    + iter->tr = &global_trace;
    + iter->trace = current_trace;
    + iter->cpu_file = TRACE_PIPE_ALL_CPU;
    +}
    +
    static void
    __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
    {
    @@ -4454,8 +4453,10 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
    if (disable_tracing)
    ftrace_kill();

    + trace_init_global_iter(&iter);
    +
    for_each_tracing_cpu(cpu) {
    - atomic_inc(&global_trace.data[cpu]->disabled);
    + atomic_inc(&iter.tr->data[cpu]->disabled);
    }

    old_userobj = trace_flags & TRACE_ITER_SYM_USEROBJ;
    @@ -4504,7 +4505,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
    iter.iter_flags |= TRACE_FILE_LAT_FMT;
    iter.pos = -1;

    - if (find_next_entry_inc(&iter) != NULL) {
    + if (trace_find_next_entry_inc(&iter) != NULL) {
    int ret;

    ret = print_trace_line(&iter);
    @@ -4526,7 +4527,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
    trace_flags |= old_userobj;

    for_each_tracing_cpu(cpu) {
    - atomic_dec(&global_trace.data[cpu]->disabled);
    + atomic_dec(&iter.tr->data[cpu]->disabled);
    }
    tracing_on();
    }
    diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
    index 2cd9639..0605fc0 100644
    --- a/kernel/trace/trace.h
    +++ b/kernel/trace/trace.h
    @@ -338,6 +338,14 @@ struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
    struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
    int *ent_cpu, u64 *ent_ts);

    +int trace_empty(struct trace_iterator *iter);
    +
    +void *trace_find_next_entry_inc(struct trace_iterator *iter);
    +
    +void trace_init_global_iter(struct trace_iterator *iter);
    +
    +void tracing_iter_reset(struct trace_iterator *iter, int cpu);
    +
    void default_wait_pipe(struct trace_iterator *iter);
    void poll_wait_pipe(struct trace_iterator *iter);

    @@ -380,6 +388,15 @@ void tracing_start_sched_switch_record(void);
    int register_tracer(struct tracer *type);
    void unregister_tracer(struct tracer *type);
    int is_tracing_stopped(void);
    +enum trace_file_type {
    + TRACE_FILE_LAT_FMT = 1,
    + TRACE_FILE_ANNOTATE = 2,
    +};
    +
    +extern cpumask_var_t __read_mostly tracing_buffer_mask;
    +
    +#define for_each_tracing_cpu(cpu) \
    + for_each_cpu(cpu, tracing_buffer_mask)

    extern int process_new_ksym_entry(char *ksymname, int op, unsigned long addr);

    @@ -471,6 +488,8 @@ trace_array_vprintk(struct trace_array *tr,
    unsigned long ip, const char *fmt, va_list args);
    int trace_array_printk(struct trace_array *tr,
    unsigned long ip, const char *fmt, ...);
    +void trace_printk_seq(struct trace_seq *s);
    +enum print_line_t print_trace_line(struct trace_iterator *iter);

    extern unsigned long trace_flags;

    diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
    new file mode 100644
    index 0000000..44cbda2
    --- /dev/null
    +++ b/kernel/trace/trace_kdb.c
    @@ -0,0 +1,119 @@
    +/*
    + * kdb helper for dumping the ftrace buffer
    + *
    + * Copyright (C) 2010 Jason Wessel <jason.wessel@windriver.com>
    + *
    + * ftrace_dump_buf based on ftrace_dump:
    + * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
    + * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
    + *
    + */
    +#include <linux/init.h>
    +#include <linux/kgdb.h>
    +#include <linux/kdb.h>
    +#include <linux/ftrace.h>
    +
    +#include "../debug/kdb/kdb_private.h"
    +#include "trace.h"
    +#include "trace_output.h"
    +
    +static void ftrace_dump_buf(int skip_lines)
    +{
    + /* use static because iter can be a bit big for the stack */
    + static struct trace_iterator iter;
    + unsigned int old_userobj;
    + int cnt = 0, cpu;
    +
    + trace_init_global_iter(&iter);
    +
    + for_each_tracing_cpu(cpu) {
    + atomic_inc(&iter.tr->data[cpu]->disabled);
    + }
    +
    + old_userobj = trace_flags;
    +
    + /* don't look at user memory in panic mode */
    + trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
    +
    + kdb_printf("Dumping ftrace buffer:\n");
    +
    + /* reset all but tr, trace, and overruns */
    + memset(&iter.seq, 0,
    + sizeof(struct trace_iterator) -
    + offsetof(struct trace_iterator, seq));
    + iter.iter_flags |= TRACE_FILE_LAT_FMT;
    + iter.pos = -1;
    +
    + for_each_tracing_cpu(cpu) {
    + iter.buffer_iter[cpu] =
    + ring_buffer_read_prepare(iter.tr->buffer, cpu);
    + ring_buffer_read_start(iter.buffer_iter[cpu]);
    + tracing_iter_reset(&iter, cpu);
    + }
    +
    + if (!trace_empty(&iter))
    + trace_find_next_entry_inc(&iter);
    + while (!trace_empty(&iter)) {
    + if (!cnt)
    + kdb_printf("---------------------------------\n");
    + cnt++;
    +
    + if (trace_find_next_entry_inc(&iter) != NULL && !skip_lines)
    + print_trace_line(&iter);
    + if (!skip_lines)
    + trace_printk_seq(&iter.seq);
    + else
    + skip_lines--;
    + if (KDB_FLAG(CMD_INTERRUPT))
    + goto out;
    + }
    +
    + if (!cnt)
    + kdb_printf(" (ftrace buffer empty)\n");
    + else
    + kdb_printf("---------------------------------\n");
    +
    +out:
    + trace_flags = old_userobj;
    +
    + for_each_tracing_cpu(cpu) {
    + atomic_dec(&iter.tr->data[cpu]->disabled);
    + }
    +
    + for_each_tracing_cpu(cpu)
    + if (iter.buffer_iter[cpu])
    + ring_buffer_read_finish(iter.buffer_iter[cpu]);
    +}
    +
    +/*
    + * kdb_ftdump - Dump the ftrace log buffer
    + */
    +static int kdb_ftdump(int argc, const char **argv)
    +{
    + int skip_lines = 0;
    + char *cp;
    +
    + if (argc > 1)
    + return KDB_ARGCOUNT;
    +
    + if (argc) {
    + skip_lines = simple_strtol(argv[1], &cp, 0);
    + if (*cp)
    + skip_lines = 0;
    + }
    +
    + kdb_trap_printk++;
    + ftrace_dump_buf(skip_lines);
    + kdb_trap_printk--;
    +
    + return 0;
    +}
    +
    +static __init int kdb_ftrace_register(void)
    +{
    + kdb_register_repeat("ftdump", kdb_ftdump, "", "Dump ftrace log",
    + 0, KDB_REPEAT_NONE);
    + return 0;
    +}
    +
    +late_initcall(kdb_ftrace_register);
    --
    1.6.3.3


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