linux-kernel - Re: [PATCH] [RFC] watchdog/softlockup: Fix softlockup_stop

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Message-ID: <20210922024905.1488-1-guojinhui@huawei.com>
Date:   Wed, 22 Sep 2021 10:49:05 +0800
From:   JinHui GUO <guojinhui@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <guojinhui@...wei.com>, <linux-kernel@...r.kernel.org>,
        <peterz@...radead.org>, <pmladek@...e.com>,
        <valentin.schneider@....com>
Subject: Re: [PATCH] [RFC] watchdog/softlockup: Fix softlockup_stop_all() hungtask bug

> x86_64 allnoconfig:

> ld: arch/x86/kernel/cpu/cacheinfo.o: in function `populate_cache_leaves':
> cacheinfo.c:(.text+0xa27): undefined reference to `cpu_llc_shared_map'
> ld: cacheinfo.c:(.text+0xa49): undefined reference to `cpu_llc_shared_map'

> Because the new for_each_cpu() now references `mask' and some code isn't
> able to handle that change.  There are probably other instances of this
> across all our architectures and configs.

There is another bug in file arch/x86/include/asm/smp.h. The per-cpu value
cpu_llc_shared_map is defined in file arch/x86/kernel/smpboot.c. But the
file arch/x86/kernel/smpboot.c would not be compiled while CONFIG_SMP is
not defined.

declared in file arch/x86/include/asm/smp.h:
DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);

defined in file arch/x86/kernel/smpboot.c:
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);

the stack:
cpu_llc_shared_map
cpu_llc_shared_mask
__cache_amd_cpumap_setup
__cache_cpumap_setup
populate_cache_leaves

CONFIG_SMP in makefile arch/x86/kernel/Makefile:
obj-$(CONFIG_SMP)               += smpboot.o

cpu_llc_shared_mask is just used in arch/x86/kernel/cpu/cacheinfo.c by for_each_cpu
while CONFIG_SMP is not defined:
./arch/x86/kernel/cpu/cacheinfo.c:889:          for_each_cpu(i, cpu_llc_shared_mask(cpu)) {
./arch/x86/kernel/cpu/cacheinfo.c:894:                  for_each_cpu(sibling, cpu_llc_shared_mask(cpu)) {
./arch/x86/include/asm/smp.h:22:static inline struct cpumask *cpu_llc_shared_mask(int cpu)

It can be fixed just as follow:

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h1
index 630ff08532be..f5d3ca5696b3 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -21,7 +21,12 @@ DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);

 static inline struct cpumask *cpu_llc_shared_mask(int cpu)
 {
+#ifdef CONFIG_SMP
        return per_cpu(cpu_llc_shared_map, cpu);
+#else
+ /* cpu_llc_shared_map is not defined while !CONFIG_SMP */
+ return cpu_all_mask;
+#endif
 }

 DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid);