[src/netbsd-8]: src/sys Pull up following revision(s) (requested by bouyer in...

[snj <snj%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c806551f93bf
branches:  netbsd-8
changeset: 851077:c806551f93bf
user:      snj <snj%NetBSD.org@localhost>
date:      Tue Oct 24 09:14:59 2017 +0000

description:
Pull up following revision(s) (requested by bouyer in ticket #326):
        sys/arch/arm/vfp/vfp_init.c: revision 1.54-1.55
        sys/kern/subr_pcu.c: revision 1.21
PR port-arm/52603:
There is a race here, as seen on arm with FPU:
LWP L is running but not on CPU, has its FPU state on CPU2 which
has not been released yet, so fpexc still has VFP_FPEXC_EN set in the PCB copy.
LWP L is scheduled on CPU1, CPU1 calls cpu_switchto() for L in mi_switch().
cpu_switchto() will set VFP_FPEXC_EN in the FPU's fpexc register per the
PCB fpexc copy.
Before CPU1 calls pcu_switchpoint() for L, CPU2 calls
pcu_do_op(PCU_CMD_SAVE | PCU_CMD_RELEASE) for L because it still holds its
FPU state and wants to load another lwp. This cause VFP_FPEXC_EN to
be cleared in the PCB copy, but not in CPU1's register. L's l_pcu_cpu is
set to NULL.
When CPU1 calls pcu_switchpoint() for L it see l_pcu_cpu is NULL, and doesn't
call the release callback.
Now CPU1 has its FPU enabled but with the wrong FPU state.
Fix by releasing the PCU even if l_pcu_cpu is NULL.
--
In the REENABLE case, make sur the fpexc copy in the pcb also has
VFP_FPEXC_EN set. Otherwise we could trap on every context switch even if
the CPU already has the VFP state.
--
We KASSERT((fregs->vfp_fpexc & VFP_FPEXC_EN) == 0) just before, so
enabled is always false. remove.

diffstat:

 sys/arch/arm/vfp/vfp_init.c |  19 +++++++++----------
 sys/kern/subr_pcu.c         |   7 ++++---
 2 files changed, 13 insertions(+), 13 deletions(-)

diffs (82 lines):

diff -r 7408306e1558 -r c806551f93bf sys/arch/arm/vfp/vfp_init.c
--- a/sys/arch/arm/vfp/vfp_init.c       Tue Oct 24 09:12:07 2017 +0000
+++ b/sys/arch/arm/vfp/vfp_init.c       Tue Oct 24 09:14:59 2017 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: vfp_init.c,v 1.53 2017/05/26 21:17:46 jmcneill Exp $ */
+/*      $NetBSD: vfp_init.c,v 1.53.2.1 2017/10/24 09:14:59 snj Exp $ */
 
 /*
  * Copyright (c) 2008 ARM Ltd
@@ -520,29 +520,25 @@
                curcpu()->ci_vfp_evs[1].ev_count++;
        }
 
+       KASSERT((armreg_fpexc_read() & VFP_FPEXC_EN) == 0);
        /*
         * If the VFP is already enabled we must be bouncing an instruction.
         */
        if (flags & PCU_REENABLE) {
                uint32_t fpexc = armreg_fpexc_read();
                armreg_fpexc_write(fpexc | VFP_FPEXC_EN);
+               fregs->vfp_fpexc |= VFP_FPEXC_EN;
                return;
        }
+       KASSERT((fregs->vfp_fpexc & VFP_FPEXC_EN) == 0);
 
        /*
         * Load and Enable the VFP (so that we can write the registers).
         */
-       bool enabled = fregs->vfp_fpexc & VFP_FPEXC_EN;
        fregs->vfp_fpexc |= VFP_FPEXC_EN;
        armreg_fpexc_write(fregs->vfp_fpexc);
-       if (enabled) {
-               /*
-                * If we think the VFP is enabled, it must have be
-                * disabled by vfp_state_release for another LWP so
-                * we can now just return.
-                */
-               return;
-       }
+       KASSERT(curcpu()->ci_pcu_curlwp[PCU_FPU] == NULL);
+       KASSERT(l->l_pcu_cpu[PCU_FPU] == NULL);
 
        load_vfpregs(fregs);
        armreg_fpscr_write(fregs->vfp_fpscr);
@@ -562,6 +558,9 @@
        struct vfpreg * const fregs = &pcb->pcb_vfp;
        uint32_t fpexc = armreg_fpexc_read();
 
+       KASSERT(curcpu()->ci_pcu_curlwp[PCU_FPU] == l);
+       KASSERT(curcpu() == l->l_pcu_cpu[PCU_FPU]);
+       KASSERT(curlwp == l || curlwp->l_pcu_cpu[PCU_FPU] != curcpu());
        /*
         * Enable the VFP (so we can read the registers).
         * Make sure the exception bit is cleared so that we can
diff -r 7408306e1558 -r c806551f93bf sys/kern/subr_pcu.c
--- a/sys/kern/subr_pcu.c       Tue Oct 24 09:12:07 2017 +0000
+++ b/sys/kern/subr_pcu.c       Tue Oct 24 09:14:59 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_pcu.c,v 1.20 2017/03/16 16:13:21 chs Exp $        */
+/*     $NetBSD: subr_pcu.c,v 1.20.6.1 2017/10/24 09:14:59 snj Exp $    */
 
 /*-
  * Copyright (c) 2011, 2014 The NetBSD Foundation, Inc.
@@ -52,7 +52,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_pcu.c,v 1.20 2017/03/16 16:13:21 chs Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_pcu.c,v 1.20.6.1 2017/10/24 09:14:59 snj Exp $");
 
 #include <sys/param.h>
 #include <sys/cpu.h>
@@ -110,7 +110,8 @@
                        continue;
                }
                struct cpu_info * const pcu_ci = l->l_pcu_cpu[id];
-               if (pcu_ci == NULL || pcu_ci == l->l_cpu) {
+               if (pcu_ci == l->l_cpu) {
+                       KASSERT(pcu_ci->ci_pcu_curlwp[id] == l);
                        continue;
                }
                const pcu_ops_t * const pcu = pcu_ops_md_defs[id];