> The "Timeout: Not all CPUs entered broadcast exception handler" message > will appear from time to time given enough systems, but this message does > not identify which CPUs failed to enter the broadcast exception handler. > This information would be valuable if available, for example, in order to > correlated with other hardware-oriented error messages. This commit > therefore maintains a cpumask_t of CPUs that have entered this handler, > and prints out which ones failed to enter in the event of a timeout.
I tried doing this a while back, but found that in my test case where I forced an error that would cause both threads from one core to be "missing", the output was highly unpredictable. Some random number of extra CPUs were reported as missing. After I added some extra breadcrumbs it became clear that pretty much all the CPUs (except the missing pair) entered do_machine_check(), but some got hung up at various points beyond the entry point. My only theory was that they were trying to snoop caches from the dead core (or access some other resource held by the dead core) and so they hung too. Your code is much neater than mine ... and perhaps works in other cases, but maybe the message needs to allow for the fact that some of the cores that are reported missing may just be collateral damage from the initial problem. If I get time in the next day or two, I'll run my old test against your code to see what happens. -Tony