Mark, I tried out a kernel with the tip of CURRENT with both D24214 and D24215 applied, and I still see the problem. As well, after doing a "sysctl debug.kdb.enter=1" and viewing the stack trace there for kldunload, it appears to be similar to the one I posted in my last post.
- Eric On Mon, Mar 30, 2020 at 1:19 PM Eric Joyner <e...@freebsd.org> wrote: > 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"
