Re: [PATCH 5/6] uprobes/tracing: Kill uprobe_trace_consumer, embed uprobe_consumer into trace_uprobe

Srikar Dronamraju
2013-02-04T17:01:49Z

* Oleg Nesterov <oleg@redhat.com> [2013-01-31 20:18:29]:

> trace_uprobe->consumer and "struct uprobe_trace_consumer" add the
> unnecessary indirection and complicate the code for no reason.
>
> This patch simply embeds uprobe_consumer into "struct trace_uprobe",
> all other changes only fix the compilation errors.
>

I know this patch doesnt change the current behaviour.

We dont handle two concurrent perf record sessions for the same user
space probe. Since both sessons share the same trace_uprobe and hence
share the same consumer. Initially I had thought of having a chain in
uprobe_trace_consumer. However we dont get have enough information at
the probe_event_disable() time to detect which consumer to delete Hence
I dropped the idea of having a list of consumers attached to the
trace_uprobe.

However with allowing prefiltering, we need to have ability to
distinguish consumers. The idea of embedding uprobe_consumer within
trace_uprobe, may make the problem even more tougher to solve.

Should we document this as a TODO?

> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> kernel/trace/trace_uprobe.c | 35 ++++++-----------------------------
> 1 files changed, 6 insertions(+), 29 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 947379a..55cdc14 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -31,17 +31,11 @@
> /*
> * uprobe event core functions
> */
> -struct trace_uprobe;
> -struct uprobe_trace_consumer {
> - struct uprobe_consumer cons;
> - struct trace_uprobe *tu;
> -};
> -
> struct trace_uprobe {
> struct list_head list;
> struct ftrace_event_class class;
> struct ftrace_event_call call;
> - struct uprobe_trace_consumer *consumer;
> + struct uprobe_consumer consumer;
> struct inode *inode;
> char *filename;
> unsigned long offset;
> @@ -92,6 +86,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs)
> goto error;
>
> INIT_LIST_HEAD(&tu->list);
> + tu->consumer.handler = uprobe_dispatcher;
> return tu;
>
> error:
> @@ -543,27 +538,15 @@ static inline bool is_trace_uprobe_enabled(struct trace_uprobe *tu)
>
> static int probe_event_enable(struct trace_uprobe *tu, int flag)
> {
> - struct uprobe_trace_consumer *utc;
> int ret = 0;
>
> if (is_trace_uprobe_enabled(tu))
> return -EINTR;
>
> - utc = kzalloc(sizeof(struct uprobe_trace_consumer), GFP_KERNEL);
> - if (!utc)
> - return -EINTR;
> -
> - utc->cons.handler = uprobe_dispatcher;
> - utc->tu = tu;
> - tu->consumer = utc;
> tu->flags |= flag;
> -
> - ret = uprobe_register(tu->inode, tu->offset, &utc->cons);
> - if (ret) {
> - tu->consumer = NULL;
> + ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> + if (ret)
> tu->flags &= ~flag;
> - kfree(utc);
> - }
>
> return ret;
> }
> @@ -573,10 +556,8 @@ static void probe_event_disable(struct trace_uprobe *tu, int flag)
> if (!is_trace_uprobe_enabled(tu))
> return;
>
> - uprobe_unregister(tu->inode, tu->offset, &tu->consumer->cons);
> + uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> tu->flags &= ~flag;
> - kfree(tu->consumer);
> - tu->consumer = NULL;
> }
>
> static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
> @@ -714,13 +695,9 @@ int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type,
>
> static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
> {
> - struct uprobe_trace_consumer *utc;
> struct trace_uprobe *tu;
>
> - utc = container_of(con, struct uprobe_trace_consumer, cons);
> - tu = utc->tu;
> - if (!tu || tu->consumer != utc)
> - return 0;
> + tu = container_of(con, struct trace_uprobe, consumer);
>
> if (tu->flags & TP_FLAG_TRACE)
> uprobe_trace_func(tu, regs);
> --
> 1.5.5.1
>

--
Thanks and Regards
Srikar Dronamraju