[SMP BUG?] the return value of is_smp() is bug?

From: Wang Long
Date: Sun Aug 31 2014 - 23:36:40 EST



Hi,all

In kernel 3.17-rc2, when i set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = y
in .config file. the secondary core can not boot.

when i set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = n in .config file,
the secondary core can boot.

But this does not happen in kernel 3.10 lts kernel, Whether the
CONFIG_SMP_ON_UP is set yes or no ,the secondary core can boot.

Does the meaning of CONFIG_SMP_ON_UP changed or this is a bug in kernel 3.17-rc2 ?


I write the following patch to test the return value of is_smp().

----------------------------------------

Signed-off-by: Wang Long <long.wanglong@xxxxxxxxxx>
---
arch/arm/kernel/setup.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 84db893d..fbeb67f 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -925,6 +925,11 @@ void __init setup_arch(char **cmdline_p)
arm_dt_init_cpu_maps();
psci_init();
#ifdef CONFIG_SMP
+
+ if (is_smp() == 1)
+ printk("is_smp() return true;\n");
+ else if (is_smp() == 0)
+ printk("is_smp() return false;\n");
if (is_smp()) {
if (!mdesc->smp_init || !mdesc->smp_init()) {
if (psci_smp_available())

kernel version: 3.17-rc2

config: set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = y
command: # qemu-system-arm -M vexpress-a9 -smp 2 -m 128M -kernel arch/arm/boot/zImage -nographic
The output:

..........
is_smp() return false;
CPU: Testing write buffer coherency: ok
missing device node for CPU 0
CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
Setting up static identity map for 0x604643d8 - 0x60464430
Brought up 1 CPUs
SMP: Total of 1 processors activated.
CPU: All CPU(s) started in SVC mode.
...........

config: set CONFIG_HAVE_SMP = y and not set CONFIG_SMP_ON_UP
command: # qemu-system-arm -M vexpress-a9 -smp 2 -m 128M -kernel arch/arm/boot/zImage -nographic
The output:

.....
Memory policy: Data cache writealloc
is_smp() return true;
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 178956969942ns
......
......
CPU: Testing write buffer coherency: ok
missing device node for CPU 0
missing device node for CPU 1
CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
Setting up static identity map for 0x60463ef8 - 0x60463f50
CPU1: Booted secondary processor
CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
Brought up 2 CPUs
SMP: Total of 2 processors activated.
CPU: All CPU(s) started in SVC mode.
devtmpfs: initialized
.......

Any ideas?


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1.7.9.5
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