I've been seeing these panics with dovecot 2.2.31 (and older versions) under FreeBSD about once every 2-3 months or so.  I know it's been discussed here in the list, but I didn't see a definitive fix.  If it's been fixed, please ignore this post (sorry!).

I finally managed to observe the bug on a server that has the patch that prints out the kevent() timespec values and got:

Nov 29 16:46:27 mail dovecot: master: Panic: kevent(events=74, ts=59.1000000000) failed: Invalid argument

Looking through the code, the panic is triggered in io_loop_handler_run_internal().  The timeout values for the kevent() call are obtained by calling io_loop_get_wait_time(), which in turn calls timeout_get_wait_time() (both in ioloop.c).

The timeout is computed by subtracting the value returned by gettimeofday() from timeout->next_run, and it looks like in very rare cases the result in tv_r->tv_usec is 1000000uS (1 second).

So, it seems that if gettimeofday() returns exactly 0 microseconds, and timeout->next_run has exactly 1000000 microseconds, the kevent() call will fail (1 in 1e12 chance?).

I'm not entirely sure where timeout->next_run is computed, but looking at timeout_update_next(), it adjusts the seconds only if the microseconds are greater than 1000000:  (ioloop.c, line 235)

if (timeout->next_run.tv_usec > 1000000) {
                timeout->next_run.tv_usec -= 1000000;

It seems like the comparison here should be greater or equal, but I'm not familiar enough with the code to say with absolute certainty.

I added more debug error messages to the code in timeout_update_next(), and although I do see next_run->tv_usec at 1000000 several times a day, I haven't seen a panic since early December on any of our servers, so I decided to post this to see if this analysis makes sense.

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