On Wed, Mar 11, 2020 at 04:32:40PM -0700, Eric Joyner wrote: > Mark, > > I did get some time to get back and retry this; however your second patch > still doesn't solve the problem. Looking into it a bit, it looks like the > kldunload process isn't hitting the code you've changed; it's hanging in > epoch_wait_preempt() in if_detach_internal(), which is immediately before > epoch_drain_callbacks(). > > I did a kernel dump while it was hanging, and this is the backtrace for the > kldunload process:
I see. I think the callback can be made much simpler and avoid the problematic sched_bind() calls. I wrote a patch that allows waiting threads to lend scheduling priority to a preempted thread blocked in an epoch section, based on some code I wrote to implement preemptible SMR sections. If waiting for a running thread, the callback just spins. This might be enough to solve your problem, I posted the two lightly tested patches here: https://reviews.freebsd.org/D24214 https://reviews.freebsd.org/D24215 If we hit a situation where a reader is preempted and then its CPU is hogged by a high-priority kernel thread, this still won't be enough, but I suspect it'll solve your case. Would you be able to test? _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"