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 08/21] ring-buffer: Do not die if rb_iter_peek() fails more than thrice
Date: Sun, 29 Mar 2020 14:43:00 -0400 [thread overview]
Message-ID: <20200329184316.644936337@goodmis.org> (raw)
In-Reply-To: 20200329184252.289087453@goodmis.org
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
As the iterator will be reading a live buffer, and if the event being read
is on a page that a writer crosses, it will fail and try again, the
condition in rb_iter_peek() that only allows a retry to happen three times
is no longer valid. Allow rb_iter_peek() to retry more than three times
without killing the ring buffer, but only if rb_iter_head_event() had failed
at least once.
Link: http://lkml.kernel.org/r/20200317213416.452888193@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/ring_buffer.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3d718add73c1..475338fda969 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4012,6 +4012,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int nr_loops = 0;
+ bool failed = false;
if (ts)
*ts = 0;
@@ -4038,10 +4039,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
* to a data event, we should never loop more than three times.
* Once for going to next page, once on time extend, and
* finally once to get the event.
- * (We never hit the following condition more than thrice).
+ * We should never hit the following condition more than thrice,
+ * unless the buffer is very small, and there's a writer
+ * that is causing the reader to fail getting an event.
*/
- if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
+ if (++nr_loops > 3) {
+ RB_WARN_ON(cpu_buffer, !failed);
return NULL;
+ }
if (rb_per_cpu_empty(cpu_buffer))
return NULL;
@@ -4052,8 +4057,10 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
}
event = rb_iter_head_event(iter);
- if (!event)
+ if (!event) {
+ failed = true;
goto again;
+ }
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
--
2.25.1
next prev parent reply other threads:[~2020-03-29 18:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-29 18:42 [for-next][PATCH 00/21] tracing: Updates for v5.7 Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 01/21] tracing: Use address-of operator on section symbols Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 02/21] selftest/ftrace: Fix function trigger test to handle trace not disabling the tracer Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 03/21] tracing: Save off entry when peeking at next entry Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 04/21] ring-buffer: Have ring_buffer_empty() not depend on tracing stopped Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 05/21] ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance() Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 06/21] ring-buffer: Add page_stamp to iterator for synchronization Steven Rostedt
2020-03-29 18:42 ` [for-next][PATCH 07/21] ring-buffer: Have rb_iter_head_event() handle concurrent writer Steven Rostedt
2020-03-29 18:43 ` Steven Rostedt [this message]
2020-03-29 18:43 ` [for-next][PATCH 09/21] ring-buffer: Optimize rb_iter_head_event() Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 10/21] ring-buffer: Make resize disable per cpu buffer instead of total buffer Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 11/21] ring-buffer: Do not disable recording when there is an iterator Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 12/21] tracing: Do not disable tracing when reading the trace file Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 13/21] ring-buffer/tracing: Have iterator acknowledge dropped events Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 14/21] tracing: Have the document reflect that the trace file keeps tracing enabled Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 15/21] ftrace/kprobe: Show the maxactive number on kprobe_events Steven Rostedt
2020-03-31 13:11 ` Sasha Levin
2020-03-29 18:43 ` [for-next][PATCH 16/21] ftrace: Make function trace pid filtering a bit more exact Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 17/21] ftrace: Create set_ftrace_notrace_pid to not trace tasks Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 18/21] tracing: Create set_event_notrace_pid " Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 19/21] selftests/ftrace: Add test to test new set_ftrace_notrace_pid file Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 20/21] selftests/ftrace: Add test to test new set_event_notrace_pid file Steven Rostedt
2020-03-29 18:43 ` [for-next][PATCH 21/21] tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid Steven Rostedt
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