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The s390 idle accounting code uses a sequence counter which gets used when the per cpu idle statistics get updated and read. One assumption on read access is that only when the sequence counter is even and did not change while reading all values the result is valid. On cpu hotplug however the per cpu data structure gets initialized via a cpu hotplug notifier on CPU_ONLINE. CPU_ONLINE however is too late, since the onlined cpu is already running and might access the per cpu data. Worst case is that the data structure gets initialized while an idle thread is updating its idle statistics. This will result in an uneven sequence counter after an update. As a result user space tools like top, which access /proc/stat in order to get idle stats, will busy loop waiting for the sequence counter to become even again, which will never happen until the queried cpu will update its idle statistics again. And even then the sequence counter will only have an even value for a couple of cpu cycles. Fix this by moving the initialization of the per cpu idle statistics to cpu_init(). I prefer that solution in favor of changing the notifier to CPU_UP_PREPARE, which would be a different solution to the problem. Cc: stable@vger.kernel.org Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
99 lines
2.2 KiB
C
99 lines
2.2 KiB
C
/*
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* arch/s390/kernel/processor.c
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*
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* Copyright IBM Corp. 2008
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* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
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*/
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#define KMSG_COMPONENT "cpu"
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#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/smp.h>
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#include <linux/seq_file.h>
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#include <linux/delay.h>
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#include <linux/cpu.h>
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#include <asm/elf.h>
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#include <asm/lowcore.h>
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#include <asm/param.h>
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static DEFINE_PER_CPU(struct cpuid, cpu_id);
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/*
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* cpu_init - initializes state that is per-CPU.
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*/
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void __cpuinit cpu_init(void)
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{
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struct cpuid *id = &per_cpu(cpu_id, smp_processor_id());
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struct s390_idle_data *idle = &__get_cpu_var(s390_idle);
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get_cpu_id(id);
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atomic_inc(&init_mm.mm_count);
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current->active_mm = &init_mm;
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BUG_ON(current->mm);
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enter_lazy_tlb(&init_mm, current);
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memset(idle, 0, sizeof(*idle));
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}
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/*
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* show_cpuinfo - Get information on one CPU for use by procfs.
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*/
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static int show_cpuinfo(struct seq_file *m, void *v)
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{
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static const char *hwcap_str[10] = {
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"esan3", "zarch", "stfle", "msa", "ldisp", "eimm", "dfp",
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"edat", "etf3eh", "highgprs"
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};
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unsigned long n = (unsigned long) v - 1;
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int i;
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if (!n) {
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s390_adjust_jiffies();
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seq_printf(m, "vendor_id : IBM/S390\n"
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"# processors : %i\n"
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"bogomips per cpu: %lu.%02lu\n",
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num_online_cpus(), loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ))%100);
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seq_puts(m, "features\t: ");
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for (i = 0; i < 10; i++)
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if (hwcap_str[i] && (elf_hwcap & (1UL << i)))
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seq_printf(m, "%s ", hwcap_str[i]);
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seq_puts(m, "\n");
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}
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get_online_cpus();
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if (cpu_online(n)) {
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struct cpuid *id = &per_cpu(cpu_id, n);
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seq_printf(m, "processor %li: "
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"version = %02X, "
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"identification = %06X, "
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"machine = %04X\n",
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n, id->version, id->ident, id->machine);
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}
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put_online_cpus();
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return 0;
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}
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static void *c_start(struct seq_file *m, loff_t *pos)
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{
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return *pos < nr_cpu_ids ? (void *)((unsigned long) *pos + 1) : NULL;
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}
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static void *c_next(struct seq_file *m, void *v, loff_t *pos)
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{
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++*pos;
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return c_start(m, pos);
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}
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static void c_stop(struct seq_file *m, void *v)
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{
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}
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const struct seq_operations cpuinfo_op = {
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.start = c_start,
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.next = c_next,
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.stop = c_stop,
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.show = show_cpuinfo,
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};
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