From 4140f3d1cb2ae2b7afc4a1c8188a56276193d781 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Sat, 13 Nov 2021 13:02:04 +0000
Subject: [PATCH] arm: Fix CPU startup synchronization.
- Use load-acquire instead of (wrong) membar_consumer then load in
cpu_boot_secondary_processors and cpu_hatched_p.
=> (Could use load then membar_consumer instead but load-acquire is
shorter.)
- Issue membar_exit before setting or clearing the bit in
cpu_set_hatched and cpu_clr_mbox.
This way, everything before cpu_set_hatched or cpu_clr_mbox is
guaranteed to happen before everything after
cpu_boot_secondary_processors, which was previously not guaranteed.
---
sys/arch/arm/arm/cpu_subr.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/sys/arch/arm/arm/cpu_subr.c b/sys/arch/arm/arm/cpu_subr.c
index fcbf500fcbd6..1fca8c3f9d42 100644
--- a/sys/arch/arm/arm/cpu_subr.c
+++ b/sys/arch/arm/arm/cpu_subr.c
@@ -95,7 +95,7 @@ cpu_boot_secondary_processors(void)
const size_t off = cpuno / CPUINDEX_DIVISOR;
const u_long bit = __BIT(cpuno % CPUINDEX_DIVISOR);
- while (membar_consumer(), arm_cpu_mbox[off] & bit) {
+ while (atomic_load_acquire(&arm_cpu_mbox[off]) & bit) {
__asm __volatile ("wfe");
}
/* Add processor to kcpuset */
@@ -111,8 +111,7 @@ cpu_hatched_p(u_int cpuindex)
const u_int off = cpuindex / CPUINDEX_DIVISOR;
const u_int bit = cpuindex % CPUINDEX_DIVISOR;
- membar_consumer();
- return (arm_cpu_hatched[off] & __BIT(bit)) != 0;
+ return (atomic_load_acquire(&arm_cpu_hatched[off]) & __BIT(bit)) != 0;
}
void
@@ -122,6 +121,7 @@ cpu_set_hatched(int cpuindex)
const size_t off = cpuindex / CPUINDEX_DIVISOR;
const u_long bit = __BIT(cpuindex % CPUINDEX_DIVISOR);
+ membar_exit(); /* store-release */
atomic_or_ulong(&arm_cpu_hatched[off], bit);
dsb(ishst);
sev();
@@ -135,6 +135,7 @@ cpu_clr_mbox(int cpuindex)
const u_long bit = __BIT(cpuindex % CPUINDEX_DIVISOR);
/* Notify cpu_boot_secondary_processors that we're done */
+ membar_exit(); /* store-release */
atomic_and_ulong(&arm_cpu_mbox[off], ~bit);
dsb(ishst);
sev();