From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: [for-next][PATCH 29/29] tracing: Comment why cond_snapshot is checked outside of max_lock protection
Date: Wed, 20 Feb 2019 13:38:06 -0500 [thread overview]
Message-ID: <20190220183809.315737571@goodmis.org> (raw)
In-Reply-To: 20190220183737.034634614@goodmis.org
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Before setting tr->cond_snapshot, it must be NULL before it can be updated.
It can go to NULL when a trace event hist trigger is created or removed, and
can only be modified under the max_lock spin lock. But because it can only
be set to something other than NULL under both the max_lock spin lock as
well as the trace_types_lock, we can perform the check if it is not NULL
only under the trace_types_lock and fail out without having to grab the
max_lock spin lock.
This is very subtle, and deserves a comment.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0460cc0f28fd..2cf3c747a357 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1116,6 +1116,14 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
goto fail_unlock;
}
+ /*
+ * The cond_snapshot can only change to NULL without the
+ * trace_types_lock. We don't care if we race with it going
+ * to NULL, but we want to make sure that it's not set to
+ * something other than NULL when we get here, which we can
+ * do safely with only holding the trace_types_lock and not
+ * having to take the max_lock.
+ */
if (tr->cond_snapshot) {
ret = -EBUSY;
goto fail_unlock;
--
2.20.1
prev parent reply other threads:[~2019-02-20 18:38 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-20 18:37 [for-next][PATCH 00/29] tracing: Updates for 5.1 Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 01/29] function_graph: Support displaying relative timestamp Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 02/29] tracing: Annotate implicit fall through in parse_probe_arg() Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 03/29] tracing: Annotate implicit fall through in predicate_parse() Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 04/29] tracing: Add comment to predicate_parse() about "&&" or "||" Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 05/29] tracing: Show more info for funcgraph wakeup tracers Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 06/29] tracing: Put a margin between flags and duration for " Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 07/29] tracing/doc: Add latency tracer funcgraph example Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 08/29] tracing: Show stacktrace for wakeup tracers Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 09/29] ring-buffer: Remove unused function ring_buffer_page_len() Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 10/29] tracing: Change the function format to display function names by perf Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 11/29] ftrace: Allow enabling of filters via index of available_filter_functions Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 12/29] uprobes: convert uprobe.ref to refcount_t Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 13/29] tracing: No need to free iter->trace in fail path of tracing_open_pipe() Steven Rostedt
2019-02-20 18:46 ` Steven Rostedt
2019-02-20 18:50 ` Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 14/29] tracing: Refactor hist trigger action code Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 15/29] tracing: Make hist trigger Documentation better reflect actions/handlers Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 16/29] tracing: Split up onmatch action data Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 17/29] tracing: Generalize hist trigger onmax and save action Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 18/29] tracing: Add conditional snapshot Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 19/29] tracing: Add hist trigger snapshot() action Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 20/29] tracing: Add hist trigger snapshot() action Documentation Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 21/29] tracing: Add hist trigger onchange() handler Steven Rostedt
2019-02-20 18:37 ` [for-next][PATCH 22/29] tracing: Add hist trigger onchange() handler Documentation Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 23/29] tracing: Add alternative synthetic event trace action syntax Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 24/29] tracing: Add SPDX license GPL-2.0 license identifier to inter-event testcases Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 25/29] tracing: Add hist trigger snapshot() action test case Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 26/29] tracing: Add hist trigger onchange() handler " Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 27/29] tracing: Add alternative synthetic event trace action " Steven Rostedt
2019-02-20 18:38 ` [for-next][PATCH 28/29] tracing: Add hist trigger action expected fail " Steven Rostedt
2019-02-20 18:38 ` Steven Rostedt [this message]
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