From: fche@redhat.com (Frank Ch. Eigler)
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Berg <johannes.berg@intel.com>
Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs
Date: Mon, 10 Mar 2014 22:41:31 -0400 [thread overview]
Message-ID: <y0mr469e9t0.fsf@fche.csb> (raw)
In-Reply-To: <241011797.35066.1394481694124.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Mon, 10 Mar 2014 20:01:34 +0000 (UTC)")
Hi -
>> From: Steven Rostedt <rostedt@goodmis.org>
>>
>> Tracepoints were made to allow enabling a tracepoint in a module before that
>> module was loaded. When a tracepoint is enabled and it does not exist, the
>> name is stored and will be enabled when the tracepoint is created.
>>
>> The problem with this approach is that when a tracepoint is enabled when
>> it expects to be there, it gives no warning that it does not exist.
So it is a deferred-activation kind of call, with no way of knowing
when or if the tracepoints will start coming in. Why is that
supported at all, considering that clients could monitor modules
coming & going via the module_notifier chain, and update registration
at that time?
>> + entry = get_tracepoint(name);
>> + /* Make sure the entry was enabled */
>> + if (!entry || !entry->enabled)
>> + ret = -ENODEV;
For what it's worth, I agree with Mathieu that this sort of successful
failure result code is a problem for tracking what needs cleanup and
what doesn't. (In systemtap's case, if this change gets merged, we'll
have to treat -ENODEV as if it were 0.)
- FChE
next prev parent reply other threads:[~2014-03-11 2:41 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-07 15:09 [for-next][PATCH 00/20] tracing: linux-next updates Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 01/20] ftrace/x86: Run a sync after fixup on failure Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 02/20] ftrace/x86: One more missing sync after fixup of function modification failure Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 03/20] tracepoint: Do not waste memory on mods with no tracepoints Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 04/20] ftrace/x86: Have ftrace_write() return -EPERM and clean up callers Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 05/20] tracing: Move raw output code from macro to standalone function Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 06/20] tracing: Move event storage for array " Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 07/20] tracing: Use helper functions in event assignment to shrink macro size Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs Steven Rostedt
2014-03-10 20:01 ` Mathieu Desnoyers
2014-03-10 20:19 ` Steven Rostedt
2014-03-10 20:55 ` Mathieu Desnoyers
2014-03-11 2:41 ` Frank Ch. Eigler [this message]
2014-03-11 2:58 ` Steven Rostedt
2014-03-11 4:08 ` Mathieu Desnoyers
2014-03-11 14:46 ` Steven Rostedt
2014-03-11 14:26 ` Frank Ch. Eigler
2014-03-11 15:06 ` Mathieu Desnoyers
2014-03-11 15:40 ` Steven Rostedt
2014-03-11 17:34 ` Mathieu Desnoyers
2014-03-11 19:13 ` Steven Rostedt
2014-03-12 14:24 ` Mathieu Desnoyers
2014-03-12 15:11 ` Steven Rostedt
2014-03-12 15:46 ` Steven Rostedt
2014-03-12 16:05 ` Mathieu Desnoyers
2014-03-12 16:18 ` Steven Rostedt
2014-03-12 16:39 ` Mathieu Desnoyers
2014-03-12 17:50 ` Steven Rostedt
2014-03-12 18:47 ` Mathieu Desnoyers
2014-03-12 18:58 ` Steven Rostedt
2014-03-12 19:30 ` Steven Rostedt
2014-03-12 19:58 ` Mathieu Desnoyers
2014-03-12 19:51 ` Mathieu Desnoyers
2014-03-12 20:35 ` Andi Kleen
2014-03-12 20:47 ` Mathieu Desnoyers
2014-03-13 3:15 ` Andi Kleen
2014-03-13 3:21 ` Mathieu Desnoyers
2014-03-13 0:49 ` Steven Rostedt
2014-03-13 3:10 ` Mathieu Desnoyers
2014-03-13 15:24 ` Mathieu Desnoyers
2014-03-12 16:40 ` Mathieu Desnoyers
2014-03-12 18:02 ` Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 09/20] tracing: Fix event header writeback.h to include tracepoint.h Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 10/20] tracing: Fix event header migrate.h " Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 11/20] tracing/module: Replace include of tracepoint.h with jump_label.h in module.h Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 12/20] tracing: Correctly expand len expressions from __dynamic_array macro Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 13/20] tracing: Evaluate len expression only once in " Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 14/20] ftrace: Cleanup of global variables ftrace_new_pgs and ftrace_update_cnt Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 15/20] ftrace: Inline the code from ftrace_dyn_table_alloc() Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 16/20] ftrace: Pass retval through return in ftrace_dyn_arch_init() Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 17/20] ftrace: Do not pass data to ftrace_dyn_arch_init Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 18/20] ftrace: Remove freelist from struct dyn_ftrace Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 19/20] ftrace: Warn on error when modifying ftrace function Steven Rostedt
2014-03-07 15:09 ` [for-next][PATCH 20/20] ftrace/x86: BUG when ftrace recovery fails Steven Rostedt
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