Reading from the 'trace' file after force stopping (by signal) consuming
read reveals there are stale trace entries in the output, this patch fixes
the bug by resetting read/write pointers of reader page after the consuming
read is stopped by force.
The issue can be reproduced as below:
echo 0 > tracing_on
echo function > current_tracer
echo 1 > tracing_on
1, read the trace file as normal
cat trace | head -n 20
...
cat trace | head -n 20
The trace entries are changing at the head of the output.
NOTE:
If it's not changing at the start please repeat the reading
several times because the tracer need time to fill up the
whole buffer.
2, read the trace file after stopping 'cat trace_pipe' by Ctrl-C
cat trace_pipe
Ctrl-C
cat trace | head -n 200
...
cat trace | head -n 200
The trace entries at the head of the output stop changing,
followed by changing trace entries.
NOTE:
Please carefully check the time stamps of the trace entries,
the time stamps of some of them at the head stop changing
in the consecutive read.
The results of test 1 and 2 are not consistent with respect to the
updating of trace buffers, some part of the trace buffers are
not updated in the test 2 while all of them are updated in the
test 1.
And the result of test 1 is correct because the trace entries
supposed to be changed for the reason the tracer works under
overwrite mode by default.
Thanks
Shan Hai
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