Much of the code sitting in arch/x86/kernel/apic/hw_nmi.c to support safe all-cpu backtracing from NMI has been copied to printk.c to make it accessible to other architectures.
Port the x86 NMI backtrace to the generic code.
Signed-off-by: Daniel Thompson daniel.thompson@linaro.org Cc: Steven Rostedt rostedt@goodmis.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: x86@kernel.org --- arch/x86/Kconfig | 1 + arch/x86/kernel/apic/hw_nmi.c | 94 ++++--------------------------------------- 2 files changed, 8 insertions(+), 87 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index ba397bde7948..f36d3058968e 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -138,6 +138,7 @@ config X86 select HAVE_ACPI_APEI_NMI if ACPI select ACPI_LEGACY_TABLES_LOOKUP if ACPI select X86_FEATURE_NAMES if PROC_FS + select ARCH_WANT_NMI_PRINTK if X86_LOCAL_APIC
config INSTRUCTION_DECODER def_bool y diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c index 6873ab925d00..7d4a5c8ac510 100644 --- a/arch/x86/kernel/apic/hw_nmi.c +++ b/arch/x86/kernel/apic/hw_nmi.c @@ -32,26 +32,6 @@ u64 hw_nmi_get_sample_period(int watchdog_thresh) static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly; static cpumask_t printtrace_mask;
-#define NMI_BUF_SIZE 4096 - -struct nmi_seq_buf { - unsigned char buffer[NMI_BUF_SIZE]; - struct seq_buf seq; -}; - -/* Safe printing in NMI context */ -static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq); - -/* "in progress" flag of arch_trigger_all_cpu_backtrace */ -static unsigned long backtrace_flag; - -static void print_seq_line(struct nmi_seq_buf *s, int start, int end) -{ - const char *buf = s->buffer + start; - - printk("%.*s", (end - start) + 1, buf); -} - void arch_trigger_all_cpu_backtrace(bool include_self) { struct nmi_seq_buf *s; @@ -60,28 +40,18 @@ void arch_trigger_all_cpu_backtrace(bool include_self) int i; int this_cpu = get_cpu();
- if (test_and_set_bit(0, &backtrace_flag)) { + if (0 != prepare_nmi_printk(to_cpumask(backtrace_mask))) { /* - * If there is already a trigger_all_cpu_backtrace() in progress - * (backtrace_flag == 1), don't output double cpu dump infos. + * If there is already an nmi printk sequence in + * progress then just give up... */ put_cpu(); return; }
- cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask); if (!include_self) cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask)); - cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask)); - /* - * Set up per_cpu seq_buf buffers that the NMIs running on the other - * CPUs will write to. - */ - for_each_cpu(cpu, to_cpumask(backtrace_mask)) { - s = &per_cpu(nmi_print_seq, cpu); - seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE); - }
if (!cpumask_empty(to_cpumask(backtrace_mask))) { pr_info("sending NMI to %s CPUs:\n", @@ -97,73 +67,23 @@ void arch_trigger_all_cpu_backtrace(bool include_self) touch_softlockup_watchdog(); }
- /* - * Now that all the NMIs have triggered, we can dump out their - * back traces safely to the console. - */ - for_each_cpu(cpu, &printtrace_mask) { - int last_i = 0; - - s = &per_cpu(nmi_print_seq, cpu); - len = seq_buf_used(&s->seq); - if (!len) - continue; - - /* Print line by line. */ - for (i = 0; i < len; i++) { - if (s->buffer[i] == '\n') { - print_seq_line(s, last_i, i); - last_i = i + 1; - } - } - /* Check if there was a partial line. */ - if (last_i < len) { - print_seq_line(s, last_i, len - 1); - pr_cont("\n"); - } - } - - clear_bit(0, &backtrace_flag); - smp_mb__after_atomic(); + complete_nmi_printk(&printtrace_mask); put_cpu(); }
-/* - * It is not safe to call printk() directly from NMI handlers. - * It may be fine if the NMI detected a lock up and we have no choice - * but to do so, but doing a NMI on all other CPUs to get a back trace - * can be done with a sysrq-l. We don't want that to lock up, which - * can happen if the NMI interrupts a printk in progress. - * - * Instead, we redirect the vprintk() to this nmi_vprintk() that writes - * the content into a per cpu seq_buf buffer. Then when the NMIs are - * all done, we can safely dump the contents of the seq_buf to a printk() - * from a non NMI context. - */ -static int nmi_vprintk(const char *fmt, va_list args) -{ - struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq); - unsigned int len = seq_buf_used(&s->seq); - - seq_buf_vprintf(&s->seq, fmt, args); - return seq_buf_used(&s->seq) - len; -} - static int arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs) { int cpu; + printk_func_t orig;
cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) { - printk_func_t printk_func_save = this_cpu_read(printk_func); - - /* Replace printk to write into the NMI seq */ - this_cpu_write(printk_func, nmi_vprintk); + orig = this_cpu_begin_nmi_printk(); printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu); show_regs(regs); - this_cpu_write(printk_func, printk_func_save); + this_cpu_end_nmi_printk(orig);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); return NMI_HANDLED;