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Date: Thu, 24 Oct 2019 09:00:37 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Divya Indi <divya.indi@...cle.com>
Cc: linux-kernel@...r.kernel.org, Joe Jin <joe.jin@...cle.com>,
Srinivas Eeda <srinivas.eeda@...cle.com>,
Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Subject: Re: [PATCH 4/5] tracing: Handle the trace array ref counter in new
functions
On Wed, 23 Oct 2019 15:57:49 -0700
Divya Indi <divya.indi@...cle.com> wrote:
> Hi Steven,
>
> A few clarifications on this discussion on reference counter -
>
> 1) We will still need to export trace_array_put() to be used for every
> trace_array_get_by_name() OR trace_array_create() + trace_array_get().
I'm fine with exporting trace_array_put, and even trace_array_get.
>
> How else will we reduce the reference counter [For eg: When multiple modules
> lookup the same trace array (say, reference counter = 4)]?
>
> 2) tr = trace_array_create("my_tr");
> trace_array_get(tr);
>
> Both of these functions will iterate through the list of trace arrays to verify
> whether the trace array exists (redundant, but more intuitive? Does this seem
> acceptable?)
>
> To avoid iterating twice, we went with increasing ref_ctr in trace_array_create.
> This necessitated a trace_array_put() in instance_mkdir (Or as suggested below,
> we can do this trace_array_put() in instance_rmdir().)
>
>
> 3) A summary of suggested changes (Let me know if this looks good) -
>
> tr = trace_array_get_by_name("foo-bar"); // ref_ctr++.
>
> if (!tr)
> {
> // instance_mkdir also causes ref_ctr = 1
You'll need locking for anyone who does this, and check the return
status below for "foo-bar" existing already (due to another thread
jumping in here).
-- Steve
> tr = trace_array_create("foo-bar"); // ref_ctr = 1
> trace_array_get(tr); // ref_ctr++
> }
>
> trace_array_printk(.....);
> trace_array_set_clr_event(......);
> ...
> ...
> ...
> // Done using the trace array.
> trace_array_put(tr); // ref_ctr--
> ...
> ...
> ...
> // We can now remove the trace array via trace_array_destroy or instance_rmdir()
> trace_array_destroy(tr); // ref_ctr > 1 returns -EBUSY.
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