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    SubjectRe: [PATCH -tip ] [BUGFIX]tracing/kprobes: Fix kprobe-tracer to support stack trace
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    On Thu, 2011-05-12 at 19:22 +0900, Masami Hiramatsu wrote:
    > 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.
    >

    Hi Masami,

    I'm working to get a "fix" patch set push out, and I included this
    patch. But when I ran it on my arch test (compiling on other archs),
    this patch broke the following:

    arm, blackfin, powerpc, s390.

    (Note, due to other bugs, UML and mips does not build to test)

    The problem is that these archs do not implement a:

    save_stack_trace_regs() function.

    I'm stripping this patch out of my next pull request, and it may need to
    wait till 2.6.41/2.8.1/3.1.

    -- Steve

    > e.g.
    >
    > # echo p schedule > /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
    > # tracer: nop
    > #
    > # TASK-PID CPU# TIMESTAMP FUNCTION
    > # | | | | |
    > sshd-1549 [001] 857.326335: p_schedule_0: (schedule+0x0/0x900)
    > sshd-1549 [001] 857.326337: <stack trace>
    > => schedule_hrtimeout_range
    > => poll_schedule_timeout
    > => do_select
    > => core_sys_select
    > => sys_select
    > => system_call_fastpath
    > tee-1751 [000] 857.326394: p_schedule_0: (schedule+0x0/0x900)
    > tee-1751 [000] 857.326395: <stack trace>
    > => do_group_exit
    > => sys_exit_group
    > => system_call_fastpath
    > <idle>-0 [001] 857.326406: p_schedule_0: (schedule+0x0/0x900)
    > <idle>-0 [001] 857.326407: <stack trace>
    > => start_secondary
    >
    > Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    > Cc: Steven Rostedt <rostedt@goodmis.org>
    > Cc: Frederic Weisbecker <fweisbec@gmail.com>
    > Cc: Ingo Molnar <mingo@redhat.com>
    > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Cc: linux-kernel@vger.kernel.org
    > ---
    > include/linux/ftrace_event.h | 4 ++++
    > kernel/trace/trace.c | 35 ++++++++++++++++++++++++++++++-----
    > kernel/trace/trace.h | 9 +++++++++
    > kernel/trace/trace_kprobe.c | 6 ++++--
    > 4 files changed, 47 insertions(+), 7 deletions(-)
    >
    > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
    > index b5a550a..bca2499 100644
    > --- a/include/linux/ftrace_event.h
    > +++ b/include/linux/ftrace_event.h
    > @@ -117,6 +117,10 @@ 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 ee9c921..bf12209 100644
    > --- a/kernel/trace/trace.c
    > +++ b/kernel/trace/trace.c
    > @@ -1191,6 +1191,18 @@ 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)
    > {
    > @@ -1236,7 +1248,7 @@ 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;
    > @@ -1255,24 +1267,36 @@ 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(&trace, regs);
    > + 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);
    > }
    >
    > /**
    > @@ -1288,7 +1312,8 @@ 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 5e9dfc6..cbce5e4 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 */




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