Date: Thu, 23 Jan 2020 13:20:16 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Ryan Libby <rlibby@freebsd.org> Cc: src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org>, Mark Johnston <markj@freebsd.org> Subject: Re: svn commit: r356919 - head/sys/x86/x86 Message-ID: <20200123112016.GS4808@kib.kiev.ua> In-Reply-To: <CAHgpiFzfiLT4tuHkK0yzhnCah-zUWrrQSVd-k%2Buv3gzgA4_a9w@mail.gmail.com> References: <202001201723.00KHN3tX093432@repo.freebsd.org> <CAHgpiFzfiLT4tuHkK0yzhnCah-zUWrrQSVd-k%2Buv3gzgA4_a9w@mail.gmail.com>
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On Wed, Jan 22, 2020 at 06:39:22PM -0800, Ryan Libby wrote: > On Mon, Jan 20, 2020 at 9:23 AM Konstantin Belousov <kib@freebsd.org> wrote: > > > > Author: kib > > Date: Mon Jan 20 17:23:03 2020 > > New Revision: 356919 > > URL: https://svnweb.freebsd.org/changeset/base/356919 > > > > Log: > > x86: Wait for curthread to be set up as an indicator that the boot stack > > is no longer used. > > > > pc_curthread is set by cpu_switch after it stopped using the old > > thread (or boot) stack. This makes the smp_after_idle_runnable() > > function not dependent on the internals of the scheduler operations. > > > > Reviewed by: markj > > Sponsored by: The FreeBSD Foundation > > MFC after: 1 week > > Differential revision: https://reviews.freebsd.org/D23276 > > > > Modified: > > head/sys/x86/x86/mp_x86.c > > > > Modified: head/sys/x86/x86/mp_x86.c > > ============================================================================== > > --- head/sys/x86/x86/mp_x86.c Mon Jan 20 16:59:39 2020 (r356918) > > +++ head/sys/x86/x86/mp_x86.c Mon Jan 20 17:23:03 2020 (r356919) > > @@ -1092,13 +1092,12 @@ init_secondary_tail(void) > > static void > > smp_after_idle_runnable(void *arg __unused) > > { > > - struct thread *idle_td; > > + struct pcpu *pc; > > int cpu; > > > > for (cpu = 1; cpu < mp_ncpus; cpu++) { > > - idle_td = pcpu_find(cpu)->pc_idlethread; > > - while (atomic_load_int(&idle_td->td_lastcpu) == NOCPU && > > - atomic_load_int(&idle_td->td_oncpu) == NOCPU) > > + pc = pcpu_find(cpu); > > + while (atomic_load_ptr(&pc->pc_curthread) == (uintptr_t)NULL) > > cpu_spinwait(); > > kmem_free((vm_offset_t)bootstacks[cpu], kstack_pages * > > PAGE_SIZE); > > _______________________________________________ > > svn-src-all@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/svn-src-all > > To unsubscribe, send any mail to "svn-src-all-unsubscribe@freebsd.org" > > I'm hitting a boot panic on a KVM VM that I think is because of this. > I don't think this works as advertised, because init_secondary_tail sets > curthread to its idlethread *itself* before it calls sched_switch. So I > think the current check is not enough to know that we're actually off > the bootstack. > > My panic is an AP page faults in the middle of init_secondary_tail, > after curthread is set. Weirdly, I only seem to hit it when I have > disabled some CPUs (to test D23318). I think this must just be > affecting some aspect of the timing. Supposed fix is https://reviews.freebsd.org/D23330
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