On Fri, Sep 06, 2013 at 01:37:01PM -0600, David Ahern wrote:
> When processing events the session code has an ordered samples queue which is
> used to time-sort events coming in across multiple mmaps. At a later point in
> time samples on the queue are flushed up to some timestamp at which point the
> event is actually processed.
>
> When analyzing events live (ie., record/analysis path in the same command)
> there is a race that leads to corrupted events and parse errors which cause
> perf to terminate. The problem is that when the event is placed in the ordered
> samples queue it is only a reference to the event which is really sitting in
> the mmap buffer. Even though the event is queued for later processing the mmap
> tail pointer is updated which indicates to the kernel that the event has been
> processed. The race is flushing the event from the queue before it gets
> overwritten by some other event. For commands trying to process events live
> (versus just writing to a file) and processing a high rate of events this
> leads
> to parse failures and perf terminates.
hi,
'perf top -G dwarf' hit this due to longer callchains
processing your patch fixed that, thanks! ;-)
>
> Examples hitting this problem are 'perf kvm stat live', especially with nested
> VMs which generate 100,000+ traces per second, and a command processing
> scheduling events with a high rate of context switching -- e.g., running
> 'perf bench sched pipe'.
>
> This patch offers live commands an option to copy the event when it is placed
> in
> the ordered samples queue.
>
SNIP
>
> new->timestamp = timestamp;
> new->file_offset = file_offset;
> - new->event = event;
> +
> + if (s->copy_on_queue) {
> + new->event = malloc(event->header.size);
> + memcpy(new->event, event, event->header.size);
missing allocation error check
jirka
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