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    Date
    SubjectRe: [PATCH -tip v5 4/7] tracing: add kprobe-based event tracer
    From
    Hi,

    2009/5/9 Masami Hiramatsu <mhiramat@redhat.com>:
    > Add kprobes based event tracer on ftrace.
    >
    > This tracer is similar to the events tracer which is based on Tracepoint
    > infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
    > and kretprobe). It probes anywhere where kprobes can probe(this means, all
    > functions body except for __kprobes functions).
    >
    > Changes from v4:
    >  - Change interface name from 'kprobe_probes' to 'kprobe_events'
    >  - Skip comments (words after '#') from inputs of 'kprobe_events'.
    >
    > Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
    > Cc: Steven Rostedt <rostedt@goodmis.org>
    > Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    > Cc: Ingo Molnar <mingo@elte.hu>
    > Cc: Frederic Weisbecker <fweisbec@gmail.com>
    > ---
    >
    >  Documentation/trace/ftrace.txt |   55 +++++
    >  kernel/trace/Kconfig           |    9 +
    >  kernel/trace/Makefile          |    1
    >  kernel/trace/trace_kprobe.c    |  404 ++++++++++++++++++++++++++++++++++++++++
    >  4 files changed, 469 insertions(+), 0 deletions(-)
    >  create mode 100644 kernel/trace/trace_kprobe.c
    >
    > diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
    > index fd9a3e6..2b8ead6 100644
    > --- a/Documentation/trace/ftrace.txt
    > +++ b/Documentation/trace/ftrace.txt
    > @@ -1310,6 +1310,61 @@ dereference in a kernel module:
    >  [...]
    >
    >
    > +kprobe-based event tracer
    > +---------------------------
    > +
    > +This tracer is similar to the events tracer which is based on Tracepoint
    > +infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
    > +and kretprobe). It probes anywhere where kprobes can probe(this means, all
    > +functions body except for __kprobes functions).
    > +
    > +Unlike the function tracer, this tracer can probe instructions inside of
    > +kernel functions. It allows you to check which instruction has been executed.
    > +
    > +Unlike the Tracepoint based events tracer, this tracer can add new probe points
    > +on the fly.
    > +
    > +Similar to the events tracer, this tracer doesn't need to be activated via
    > +current_tracer, instead of that, just set probe points via
    > +/debug/tracing/kprobe_events.
    > +
    > +Synopsis of kprobe_events:
    > +  p SYMBOL[+offs|-offs]|MEMADDR        : set a probe
    > +  r SYMBOL[+0]                 : set a return probe
    > +
    > +E.g.
    > +  echo p sys_open > /debug/tracing/kprobe_events
    > +
    > + This sets a kprobe on the top of sys_open() function.
    > +
    > +  echo r sys_open >> /debug/tracing/kprobe_events
    > +
    > + This sets a kretprobe on the return point of sys_open() function.
    > +
    > +  echo > /debug/tracing/kprobe_events
    > +
    > + This clears all probe points. and you can see the traced information via
    > +/debug/tracing/trace.
    > +
    > +  cat /debug/tracing/trace
    > +# tracer: nop
    > +#
    > +#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
    > +#              | |       |          |         |
    > +           <...>-5117  [003]   416.481638: sys_open: @sys_open+0
    > +           <...>-5117  [003]   416.481662: syscall_call: <-sys_open+0
    > +           <...>-5117  [003]   416.481739: sys_open: @sys_open+0
    > +           <...>-5117  [003]   416.481762: sysenter_do_call: <-sys_open+0
    > +           <...>-5117  [003]   416.481818: sys_open: @sys_open+0
    > +           <...>-5117  [003]   416.481842: sysenter_do_call: <-sys_open+0
    > +           <...>-5117  [003]   416.481882: sys_open: @sys_open+0
    > +           <...>-5117  [003]   416.481905: sysenter_do_call: <-sys_open+0
    > +
    > + @SYMBOL means that kernel hits a probe, and <-SYMBOL means kernel returns
    > +from SYMBOL(e.g. "sysenter_do_call: <-sys_open+0" means kernel returns from
    > +sys_open to sysenter_do_call).
    > +
    > +
    >  function graph tracer
    >  ---------------------------
    >
    > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
    > index 7370253..914df9c 100644
    > --- a/kernel/trace/Kconfig
    > +++ b/kernel/trace/Kconfig
    > @@ -398,6 +398,15 @@ config BLK_DEV_IO_TRACE
    >
    >          If unsure, say N.
    >
    > +config KPROBE_TRACER
    > +       depends on KPROBES
    > +       depends on X86
    > +       bool "Trace kprobes"
    > +       select TRACING
    > +       help
    > +         This tracer probes everywhere where kprobes can probe it, and
    > +         records various registers and memories specified by user.
    > +
    >  config DYNAMIC_FTRACE
    >        bool "enable/disable ftrace tracepoints dynamically"
    >        depends on FUNCTION_TRACER
    > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
    > index 06b8585..166c859 100644
    > --- a/kernel/trace/Makefile
    > +++ b/kernel/trace/Makefile
    > @@ -51,5 +51,6 @@ obj-$(CONFIG_EVENT_TRACING) += trace_export.o
    >  obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
    >  obj-$(CONFIG_EVENT_PROFILE) += trace_event_profile.o
    >  obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
    > +obj-$(CONFIG_KPROBE_TRACER) += trace_kprobe.o
    >
    >  libftrace-y := ftrace.o
    > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
    > new file mode 100644
    > index 0000000..8112505
    > --- /dev/null
    > +++ b/kernel/trace/trace_kprobe.c
    > @@ -0,0 +1,404 @@
    > +/*
    > + * kprobe based kernel tracer
    > + *
    > + * Created by Masami Hiramatsu <mhiramat@redhat.com>
    > + *
    > + * This program is free software; you can redistribute it and/or modify
    > + * it under the terms of the GNU General Public License version 2 as
    > + * published by the Free Software Foundation.
    > + *
    > + * This program is distributed in the hope that it will be useful,
    > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    > + * GNU General Public License for more details.
    > + *
    > + * You should have received a copy of the GNU General Public License
    > + * along with this program; if not, write to the Free Software
    > + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    > + */
    > +
    > +#include <linux/module.h>
    > +#include <linux/uaccess.h>
    > +#include <linux/kprobes.h>
    > +#include <linux/seq_file.h>
    > +#include <linux/slab.h>
    > +#include <linux/smp.h>
    > +#include <linux/debugfs.h>
    > +#include <linux/types.h>
    > +#include <linux/string.h>
    > +#include <linux/ctype.h>
    > +
    > +#include <linux/ftrace.h>
    > +#include "trace.h"
    > +
    > +/**
    > + * kprobe_trace_core
    > + */
    > +#define TRACE_MAXARGS 6
    > +
    > +struct trace_probe {
    > +       struct list_head        list;
    > +       union {
    > +               struct kprobe           kp;
    > +               struct kretprobe        rp;
    > +       };
    > +       const char              *symbol;        /* symbol name */
    > +};
    > +
    > +static void kprobe_trace_record(unsigned long ip, struct trace_probe *tp,
    > +                               struct pt_regs *regs);
    > +
    > +static int kprobe_trace_func(struct kprobe *kp, struct pt_regs *regs)
    > +{
    > +       struct trace_probe *tp = container_of(kp, struct trace_probe, kp);
    > +
    > +       kprobe_trace_record(instruction_pointer(regs), tp, regs);
    > +       return 0;
    > +}
    > +
    > +static int kretprobe_trace_func(struct kretprobe_instance *ri,
    > +                               struct pt_regs *regs)
    > +{
    > +       struct trace_probe *tp = container_of(ri->rp, struct trace_probe, rp);
    > +
    > +       kprobe_trace_record((unsigned long)ri->ret_addr, tp, regs);
    > +       return 0;
    > +}
    > +
    > +static int probe_is_return(struct trace_probe *tp)
    > +{
    > +       return (tp->rp.handler == kretprobe_trace_func);
    > +}
    > +
    > +static const char *probe_symbol(struct trace_probe *tp)
    > +{
    > +       return tp->symbol ? tp->symbol : "unknown";
    > +}
    > +
    > +static long probe_offset(struct trace_probe *tp)
    > +{
    > +       return (probe_is_return(tp)) ? tp->rp.kp.offset : tp->kp.offset;
    > +}
    > +
    > +static void *probe_address(struct trace_probe *tp)
    > +{
    > +       return (probe_is_return(tp)) ? tp->rp.kp.addr : tp->kp.addr;
    > +}
    > +
    > +
    > +static DEFINE_MUTEX(probe_lock);
    > +static LIST_HEAD(probe_list);
    > +
    > +static struct trace_probe *alloc_trace_probe(const char *symbol)
    > +{
    > +       struct trace_probe *tp;
    > +
    > +       tp = kzalloc(sizeof(struct trace_probe), GFP_KERNEL);
    > +       if (!tp)
    > +               return ERR_PTR(-ENOMEM);
    > +
    > +       if (symbol) {
    > +               tp->symbol = kstrdup(symbol, GFP_KERNEL);
    > +               if (!tp->symbol) {
    > +                       kfree(tp);
    > +                       return ERR_PTR(-ENOMEM);
    > +               }
    > +       }
    > +
    > +       INIT_LIST_HEAD(&tp->list);
    > +       return tp;
    > +}
    > +
    > +static void free_trace_probe(struct trace_probe *tp)
    > +{
    > +       kfree(tp->symbol);
    > +       kfree(tp);
    > +}
    > +
    > +static int register_trace_probe(struct trace_probe *tp)
    > +{
    > +       int ret;
    > +
    > +       mutex_lock(&probe_lock);
    > +       list_add_tail(&tp->list, &probe_list);
    > +
    > +       if (probe_is_return(tp))
    > +               ret = register_kretprobe(&tp->rp);
    > +       else
    > +               ret = register_kprobe(&tp->kp);
    > +
    > +       if (ret) {
    > +               pr_warning("Could not insert probe(%d)\n", ret);
    > +               if (ret == -EILSEQ) {
    > +                       pr_warning("Probing address(0x%p) is not an "
    > +                                  "instruction boundary.\n",
    > +                                  probe_address(tp));
    > +                       ret = -EINVAL;
    > +               }
    > +               list_del(&tp->list);
    > +       }
    > +       mutex_unlock(&probe_lock);
    > +       return ret;
    > +}
    > +
    > +static void unregister_trace_probe(struct trace_probe *tp)
    > +{
    > +       if (probe_is_return(tp))
    > +               unregister_kretprobe(&tp->rp);
    > +       else
    > +               unregister_kprobe(&tp->kp);
    > +       list_del(&tp->list);
    > +}
    > +
    > +static int create_trace_probe(int argc, char **argv)
    > +{
    > +       /*
    > +        * Argument syntax:
    > +        *  - Add kprobe: p SYMBOL[+OFFS|-OFFS]|ADDRESS
    > +        *  - Add kretprobe: r SYMBOL[+0]
    > +        */
    > +       struct trace_probe *tp;
    > +       struct kprobe *kp;
    > +       char *tmp;
    > +       int ret = 0;
    > +       int is_return = 0;
    > +       char *symbol = NULL;
    > +       long offset = 0;
    > +       void *addr = NULL;
    > +
    > +       if (argc < 2)
    > +               return -EINVAL;
    > +
    > +       if (argv[0][0] == 'p')
    > +               is_return = 0;
    > +       else if (argv[0][0] == 'r')
    > +               is_return = 1;
    > +       else
    > +               return -EINVAL;
    > +
    > +       if (isdigit(argv[1][0])) {
    > +               if (is_return)
    > +                       return -EINVAL;
    > +               /* an address specified */
    > +               ret = strict_strtoul(&argv[0][2], 0, (unsigned long *)&addr);
    > +               if (ret)
    > +                       return ret;
    > +       } else {
    > +               /* a symbol specified */
    > +               symbol = argv[1];
    > +               /* TODO: support .init module functions */
    > +               tmp = strchr(symbol, '+');
    > +               if (!tmp)
    > +                       tmp = strchr(symbol, '-');
    > +
    > +               if (tmp) {
    > +                       /* skip sign because strict_strtol doesn't accept '+' */
    > +                       ret = strict_strtol(tmp + 1, 0, &offset);
    > +                       if (ret)
    > +                               return ret;
    > +                       if (*tmp == '-')
    > +                               offset = -offset;
    > +                       *tmp = '\0';
    > +               }
    > +               if (offset && is_return)
    > +                       return -EINVAL;
    > +       }
    > +
    > +       /* setup a probe */
    > +       tp = alloc_trace_probe(symbol);
    > +       if (IS_ERR(tp))
    > +               return PTR_ERR(tp);
    > +
    > +       if (is_return) {
    > +               kp = &tp->rp.kp;
    > +               tp->rp.handler = kretprobe_trace_func;
    > +       } else {
    > +               kp = &tp->kp;
    > +               tp->kp.pre_handler = kprobe_trace_func;
    > +       }
    > +
    > +       if (tp->symbol) {
    > +               /* TODO: check offset is collect by using insn_decoder */
    > +               kp->symbol_name = tp->symbol;
    > +               kp->offset = offset;
    > +       } else
    > +               kp->addr = addr;
    > +
    > +       ret = register_trace_probe(tp);
    > +       if (ret)
    > +               goto error;
    > +       return 0;
    > +
    > +error:
    > +       free_trace_probe(tp);
    > +       return ret;
    > +}
    > +
    > +static void cleanup_all_probes(void)
    > +{
    > +       struct trace_probe *tp;
    > +       mutex_lock(&probe_lock);
    > +       /* TODO: Use batch unregistration */
    > +       while (!list_empty(&probe_list)) {
    > +               tp = list_entry(probe_list.next, struct trace_probe, list);
    > +               unregister_trace_probe(tp);
    > +               free_trace_probe(tp);
    > +       }
    > +       mutex_unlock(&probe_lock);
    > +}
    > +
    > +
    > +/* Probes listing interfaces */
    > +static void *probes_seq_start(struct seq_file *m, loff_t *pos)
    > +{
    > +       mutex_lock(&probe_lock);
    > +       return seq_list_start(&probe_list, *pos);
    > +}
    > +
    > +static void *probes_seq_next(struct seq_file *m, void *v, loff_t *pos)
    > +{
    > +       return seq_list_next(v, &probe_list, pos);
    > +}
    > +
    > +static void probes_seq_stop(struct seq_file *m, void *v)
    > +{
    > +       mutex_unlock(&probe_lock);
    > +}
    > +
    > +static int probes_seq_show(struct seq_file *m, void *v)
    > +{
    > +       struct trace_probe *tp = v;
    > +
    > +       if (tp == NULL)
    > +               return 0;
    > +
    > +       if (tp->symbol)
    > +               seq_printf(m, "%c %s%+ld\n",
    > +                       probe_is_return(tp) ? 'r' : 'p',
    > +                       probe_symbol(tp), probe_offset(tp));
    > +       else
    > +               seq_printf(m, "%c 0x%p\n",
    > +                       probe_is_return(tp) ? 'r' : 'p',
    > +                       probe_address(tp));
    > +       return 0;
    > +}
    > +
    > +static const struct seq_operations probes_seq_op = {
    > +       .start  = probes_seq_start,
    > +       .next   = probes_seq_next,
    > +       .stop   = probes_seq_stop,
    > +       .show   = probes_seq_show
    > +};
    > +
    > +static int probes_open(struct inode *inode, struct file *file)
    > +{
    > +       if ((file->f_mode & FMODE_WRITE) &&
    > +           !(file->f_flags & O_APPEND))
    > +               cleanup_all_probes();
    > +
    > +       return seq_open(file, &probes_seq_op);
    > +}
    > +
    > +
    > +#define WRITE_BUFSIZE 128
    > +
    > +static ssize_t probes_write(struct file *file, const char __user *buffer,
    > +                           size_t count, loff_t *ppos)
    > +{
    > +       char *kbuf, *tmp;
    > +       char **argv = NULL;
    > +       int argc = 0;
    > +       int ret;
    > +       size_t done;
    > +       size_t size;
    > +
    > +       if (!count || count < 0)
    > +               return 0;
    > +
    > +       kbuf = kmalloc(WRITE_BUFSIZE, GFP_KERNEL);
    > +       if (!kbuf)
    > +               return -ENOMEM;
    > +
    > +       ret = done = 0;
    > +       do {
    > +               size = count - done;
    > +               if (size > WRITE_BUFSIZE)
    > +                       size = WRITE_BUFSIZE;
    > +               if (copy_from_user(kbuf, buffer + done, size)) {
    > +                       ret = -EFAULT;
    > +                       goto out;
    > +               }
    > +               kbuf[size] = '\0';
    > +               tmp = strchr(kbuf, '\n');
    > +               if (!tmp) {
    > +                       pr_warning("Line length is too long: "
    > +                                  "Should be less than %d.", WRITE_BUFSIZE);
    > +                       ret = -EINVAL;
    > +                       goto out;
    > +               }
    > +               *tmp = '\0';
    > +               size = tmp - kbuf + 1;
    > +               done += size;
    > +               /* Remove comments */
    > +               tmp = strchr(kbuf, '#');
    > +               if (tmp)
    > +                       *tmp = '\0';
    > +
    > +               argv = argv_split(GFP_KERNEL, kbuf, &argc);
    > +               if (!argv) {
    > +                       ret = -ENOMEM;
    > +                       goto out;
    > +               }
    > +
    > +               if (argc)
    > +                       ret = create_trace_probe(argc, argv);
    > +
    > +               argv_free(argv);
    > +               if (ret < 0)
    > +                       goto out;
    > +
    > +       } while (done < count);
    > +       ret = done;
    > +out:
    > +       kfree(kbuf);
    > +       return ret;
    > +}
    > +
    > +static const struct file_operations kprobe_events_ops = {
    > +       .owner          = THIS_MODULE,
    > +       .open           = probes_open,
    > +       .read           = seq_read,
    > +       .llseek         = seq_lseek,
    > +       .release        = seq_release,
    > +       .write          = probes_write,
    > +};
    > +
    > +/* event recording functions */
    > +static void kprobe_trace_record(unsigned long ip, struct trace_probe *tp,
    > +                               struct pt_regs *regs)
    > +{
    > +       __trace_bprintk(ip, "%s%s%+ld\n",
    > +                       probe_is_return(tp) ? "<-" : "@",
    > +                       probe_symbol(tp), probe_offset(tp));
    > +}



    What happens here if you have:

    kprobe_trace_record() {
    probe_symbol() {
    .... probes_open() {
    cleanup_all_probes() {
    free_trace_probe();
    return tp->symbol ? ....; //crack!


    I wonder if you shouldn't use a per_cpu list of probes,
    spinlocked/irqsaved accessed
    and also a kind of prevention against nmi.

    Or better, you can use rcu, but we won't be able to probe rcu functions....

    Frederic.


    > +
    > +/* Make a debugfs interface for controling probe points */
    > +static __init int init_kprobe_trace(void)
    > +{
    > +       struct dentry *d_tracer;
    > +       struct dentry *entry;
    > +
    > +       d_tracer = tracing_init_dentry();
    > +       if (!d_tracer)
    > +               return 0;
    > +
    > +       entry = debugfs_create_file("kprobe_events", 0644, d_tracer,
    > +                                   NULL, &kprobe_events_ops);
    > +
    > +       if (!entry)
    > +               pr_warning("Could not create debugfs "
    > +                          "'kprobe_events' entry\n");
    > +       return 0;
    > +}
    > +fs_initcall(init_kprobe_trace);
    > +
    >
    >
    > --
    > Masami Hiramatsu
    >
    > Software Engineer
    > Hitachi Computer Products (America) Inc.
    > Software Solutions Division
    >
    > e-mail: mhiramat@redhat.com
    >
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