Messages in this thread | | | Date | Mon, 05 Nov 2018 20:53:42 -0800 (PST) | Subject | Re: [PATCH RFC] hist lookups | From | David Miller <> |
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Jiri,
Because you now run queued_events__queue() lockless with that condvar trick, it is possible for top->qe.in to be seen as one past the data[] array, this is because the rotate_queues() code goes:
if (++top->qe.in > &top->qe.data[1]) top->qe.in = &top->qe.data[0];
So for a brief moment top->qe.in is out of range and thus perf_top__mmap_read_idx() can try to enqueue to top->qe.data[2]
We can just do:
if (top->qe.in == &top->qe.data[1]) top->qe.in = &top->qe.data[0]; else top->qe.in = &top->qe.data[1];
Or, make top->qe.in an index, and simply go:
top->qe.in ^= 1;
Either way will fix the bug.
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