On Sat, Mar 28, 2020 at 3:52 PM Mark Johnston <ma...@freebsd.org> wrote:
> 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? > Yeah, I'll try them out. - Eric _______________________________________________ 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"
