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    Subject[PATCH 16/16 v2] tracing/kprobes: Fix kprobe-tracer to support stack trace
    From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

    Fix to support kernel stack trace correctly on kprobe-tracer.
    Since the execution path of kprobe-based dynamic events is different
    from other tracepoint-based events, normal ftrace_trace_stack() doesn't
    work correctly. To fix that, this introduces ftrace_trace_stack_regs()
    which traces stack via pt_regs instead of current stack register.

    e.g.

    # echo p schedule+4 > /sys/kernel/debug/tracing/kprobe_events
    # echo 1 > /sys/kernel/debug/tracing/options/stacktrace
    # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
    # head -n 20 /sys/kernel/debug/tracing/trace
    bash-2968 [000] 10297.050245: p_schedule_4: (schedule+0x4/0x4ca)
    bash-2968 [000] 10297.050247: <stack trace>
    => schedule_timeout
    => n_tty_read
    => tty_read
    => vfs_read
    => sys_read
    => system_call_fastpath
    kworker/0:1-2940 [000] 10297.050265: p_schedule_4: (schedule+0x4/0x4ca)
    kworker/0:1-2940 [000] 10297.050266: <stack trace>
    => worker_thread
    => kthread
    => kernel_thread_helper
    sshd-1132 [000] 10297.050365: p_schedule_4: (schedule+0x4/0x4ca)
    sshd-1132 [000] 10297.050365: <stack trace>
    => sysret_careful

    Note: Even with this fix, the first entry will be skipped
    if the probe is put on the function entry area before
    the frame pointer is set up (usually, that is 4 bytes
    (push %bp; mov %sp %bp) on x86), because stack unwinder
    depends on the frame pointer.

    Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: yrl.pp-manager.tt@hitachi.com
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Namhyung Kim <namhyung@gmail.com>
    Link: http://lkml.kernel.org/r/20110608070934.17777.17116.stgit@fedora15
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    include/linux/ftrace_event.h | 4 ++++
    kernel/trace/trace.c | 34 +++++++++++++++++++++++++++++-----
    kernel/trace/trace.h | 9 +++++++++
    kernel/trace/trace_kprobe.c | 6 ++++--
    4 files changed, 46 insertions(+), 7 deletions(-)

    diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
    index 59d3ef1..b1e69ee 100644
    --- a/include/linux/ftrace_event.h
    +++ b/include/linux/ftrace_event.h
    @@ -129,6 +129,10 @@ void trace_current_buffer_unlock_commit(struct ring_buffer *buffer,
    void trace_nowake_buffer_unlock_commit(struct ring_buffer *buffer,
    struct ring_buffer_event *event,
    unsigned long flags, int pc);
    +void trace_nowake_buffer_unlock_commit_regs(struct ring_buffer *buffer,
    + struct ring_buffer_event *event,
    + unsigned long flags, int pc,
    + struct pt_regs *regs);
    void trace_current_buffer_discard_commit(struct ring_buffer *buffer,
    struct ring_buffer_event *event);

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index c977018..d9c1612 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -1193,6 +1193,18 @@ void trace_nowake_buffer_unlock_commit(struct ring_buffer *buffer,
    }
    EXPORT_SYMBOL_GPL(trace_nowake_buffer_unlock_commit);

    +void trace_nowake_buffer_unlock_commit_regs(struct ring_buffer *buffer,
    + struct ring_buffer_event *event,
    + unsigned long flags, int pc,
    + struct pt_regs *regs)
    +{
    + ring_buffer_unlock_commit(buffer, event);
    +
    + ftrace_trace_stack_regs(buffer, flags, 0, pc, regs);
    + ftrace_trace_userstack(buffer, flags, pc);
    +}
    +EXPORT_SYMBOL_GPL(trace_nowake_buffer_unlock_commit_regs);
    +
    void trace_current_buffer_discard_commit(struct ring_buffer *buffer,
    struct ring_buffer_event *event)
    {
    @@ -1238,7 +1250,7 @@ ftrace(struct trace_array *tr, struct trace_array_cpu *data,
    #ifdef CONFIG_STACKTRACE
    static void __ftrace_trace_stack(struct ring_buffer *buffer,
    unsigned long flags,
    - int skip, int pc)
    + int skip, int pc, struct pt_regs *regs)
    {
    struct ftrace_event_call *call = &event_kernel_stack;
    struct ring_buffer_event *event;
    @@ -1257,24 +1269,36 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
    trace.skip = skip;
    trace.entries = entry->caller;

    - save_stack_trace(&trace);
    + if (regs)
    + save_stack_trace_regs(regs, &trace);
    + else
    + save_stack_trace(&trace);
    if (!filter_check_discard(call, entry, buffer, event))
    ring_buffer_unlock_commit(buffer, event);
    }

    +void ftrace_trace_stack_regs(struct ring_buffer *buffer, unsigned long flags,
    + int skip, int pc, struct pt_regs *regs)
    +{
    + if (!(trace_flags & TRACE_ITER_STACKTRACE))
    + return;
    +
    + __ftrace_trace_stack(buffer, flags, skip, pc, regs);
    +}
    +
    void ftrace_trace_stack(struct ring_buffer *buffer, unsigned long flags,
    int skip, int pc)
    {
    if (!(trace_flags & TRACE_ITER_STACKTRACE))
    return;

    - __ftrace_trace_stack(buffer, flags, skip, pc);
    + __ftrace_trace_stack(buffer, flags, skip, pc, NULL);
    }

    void __trace_stack(struct trace_array *tr, unsigned long flags, int skip,
    int pc)
    {
    - __ftrace_trace_stack(tr->buffer, flags, skip, pc);
    + __ftrace_trace_stack(tr->buffer, flags, skip, pc, NULL);
    }

    /**
    @@ -1290,7 +1314,7 @@ void trace_dump_stack(void)
    local_save_flags(flags);

    /* skipping 3 traces, seems to get us at the caller of this function */
    - __ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count());
    + __ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count(), NULL);
    }

    static DEFINE_PER_CPU(int, user_stack_count);
    diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
    index 742f545..a3e2db7 100644
    --- a/kernel/trace/trace.h
    +++ b/kernel/trace/trace.h
    @@ -389,6 +389,9 @@ void update_max_tr_single(struct trace_array *tr,
    void ftrace_trace_stack(struct ring_buffer *buffer, unsigned long flags,
    int skip, int pc);

    +void ftrace_trace_stack_regs(struct ring_buffer *buffer, unsigned long flags,
    + int skip, int pc, struct pt_regs *regs);
    +
    void ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags,
    int pc);

    @@ -400,6 +403,12 @@ static inline void ftrace_trace_stack(struct ring_buffer *buffer,
    {
    }

    +static inline void ftrace_trace_stack_regs(struct ring_buffer *buffer,
    + unsigned long flags, int skip,
    + int pc, struct pt_regs *regs)
    +{
    +}
    +
    static inline void ftrace_trace_userstack(struct ring_buffer *buffer,
    unsigned long flags, int pc)
    {
    diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
    index f925c45..7053ef3 100644
    --- a/kernel/trace/trace_kprobe.c
    +++ b/kernel/trace/trace_kprobe.c
    @@ -1397,7 +1397,8 @@ static __kprobes void kprobe_trace_func(struct kprobe *kp, struct pt_regs *regs)
    store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);

    if (!filter_current_check_discard(buffer, call, entry, event))
    - trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);
    + trace_nowake_buffer_unlock_commit_regs(buffer, event,
    + irq_flags, pc, regs);
    }

    /* Kretprobe handler */
    @@ -1429,7 +1430,8 @@ static __kprobes void kretprobe_trace_func(struct kretprobe_instance *ri,
    store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);

    if (!filter_current_check_discard(buffer, call, entry, event))
    - trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);
    + trace_nowake_buffer_unlock_commit_regs(buffer, event,
    + irq_flags, pc, regs);
    }

    /* Event entry printers */
    --
    1.7.4.4



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