lkml.org 
[lkml]   [2020]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC][PATCH 06/11] ring-buffer: Do not die if rb_iter_peek() fails more than thrice
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is no longer valid.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.

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

\
 
 \ /
  Last update: 2020-03-17 22:35    [W:0.100 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site