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PR port-arm/52603:

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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.
This commit is contained in:
bouyer 2017-10-16 15:03:57 +00:00
parent 15a89934c2
commit d4ce271380
1 changed files with 4 additions and 3 deletions
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7
sys/kern/subr_pcu.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: subr_pcu.c,v 1.20 2017/03/16 16:13:21 chs Exp $ */
/* $NetBSD: subr_pcu.c,v 1.21 2017/10/16 15:03:57 bouyer 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 1.21 2017/10/16 15:03:57 bouyer Exp $");
#include <sys/param.h>
#include <sys/cpu.h>
@ -110,7 +110,8 @@ pcu_switchpoint(lwp_t *l)
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];