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ring-buffer: Do not die if rb_iter_peek() fails more than thrice
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crosses, it will fail and try again, the condition in rb_iter_peek() that only allows a retry to happen three times is no longer valid.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>
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parent
785888c544
commit
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1 changed files with 10 additions and 3 deletions
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@ -4012,6 +4012,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
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struct ring_buffer_per_cpu *cpu_buffer;
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struct ring_buffer_event *event;
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int nr_loops = 0;
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bool failed = false;
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if (ts)
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*ts = 0;
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@ -4038,10 +4039,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
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* to a data event, we should never loop more than three times.
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* Once for going to next page, once on time extend, and
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* finally once to get the event.
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* (We never hit the following condition more than thrice).
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* We should never hit the following condition more than thrice,
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* unless the buffer is very small, and there's a writer
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* that is causing the reader to fail getting an event.
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*/
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if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
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if (++nr_loops > 3) {
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RB_WARN_ON(cpu_buffer, !failed);
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return NULL;
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}
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if (rb_per_cpu_empty(cpu_buffer))
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return NULL;
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@ -4052,8 +4057,10 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
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}
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event = rb_iter_head_event(iter);
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if (!event)
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if (!event) {
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failed = true;
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goto again;
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}
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switch (event->type_len) {
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case RINGBUF_TYPE_PADDING:
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