| Message ID | 1425463974-23568-6-git-send-email-daniel.thompson@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Daniel Thompson <daniel.thompson@linaro.org> wrote: > 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. Is there any difference between the generic and the x86 code as they stand today? Thanks, Ingo
On Thu, 2015-03-05 at 01:54 +0100, Ingo Molnar wrote: > * Daniel Thompson <daniel.thompson@linaro.org> wrote: > > > 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. > > Is there any difference between the generic and the x86 code as they > stand today? Shouldn't be any user observable change but there are some changes, mostly due to review comments. 1. The seq_buf structures are initialized at boot and *after* they are consumed (originally they were initialized just before use). 2. The generic code doesn't maintain an equivalent of backtrace_mask (which was essentially a copy of cpus_online made when backtracing was requested) and instead iterates using for_each_possible_cpu() to initialize and dump the seq_buf:s. Daniel. PS The main piece that git code motion tracking should follow if I squashed the generic and x86 patches together would be nmi_vprintk(). I suspect most of the rest would be missed as the code copies is in pretty small fragments.
* Daniel Thompson <daniel.thompson@linaro.org> wrote: > On Thu, 2015-03-05 at 01:54 +0100, Ingo Molnar wrote: > > * Daniel Thompson <daniel.thompson@linaro.org> wrote: > > > > > 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. > > > > Is there any difference between the generic and the x86 code as they > > stand today? > > Shouldn't be any user observable change but there are some changes, > mostly due to review comments. > > 1. The seq_buf structures are initialized at boot and *after* they > are consumed (originally they were initialized just before use). > > 2. The generic code doesn't maintain an equivalent of backtrace_mask > (which was essentially a copy of cpus_online made when backtracing > was requested) and instead iterates using for_each_possible_cpu() > to initialize and dump the seq_buf:s. Ok, I have no fundamental objections: Acked-by: Ingo Molnar <mingo@kernel.org> I suspect you want to carry the x86 bits yourself? Thanks, Ingo
On Thu, 2015-03-05 at 20:46 +0100, Ingo Molnar wrote: > * Daniel Thompson <daniel.thompson@linaro.org> wrote: > > > On Thu, 2015-03-05 at 01:54 +0100, Ingo Molnar wrote: > > > * Daniel Thompson <daniel.thompson@linaro.org> wrote: > > > > > > > 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. > > > > > > Is there any difference between the generic and the x86 code as they > > > stand today? > > > > Shouldn't be any user observable change but there are some changes, > > mostly due to review comments. > > > > 1. The seq_buf structures are initialized at boot and *after* they > > are consumed (originally they were initialized just before use). > > > > 2. The generic code doesn't maintain an equivalent of backtrace_mask > > (which was essentially a copy of cpus_online made when backtracing > > was requested) and instead iterates using for_each_possible_cpu() > > to initialize and dump the seq_buf:s. > > Ok, I have no fundamental objections: > > Acked-by: Ingo Molnar <mingo@kernel.org> > > I suspect you want to carry the x86 bits yourself? I've done plenty of bisectability testing on this set so patches 4 and 5 could be separated from the set and go via the x86 tree. However with your ack I hope that taking the patchset via the irqchip route should be possible. Jason: After I've attended to Joe Perches/Steven Rostedt's comments will you be comfortable enough to take patches 1-5 through one of your trees? It would be great to deliver patch 6 too but rmk is having a short break so getting an ack for that may not work out Daniel.
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index c2fb8a87dccb..fbae5564a1f3 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -141,6 +141,7 @@ config X86 select ACPI_LEGACY_TABLES_LOOKUP if ACPI select X86_FEATURE_NAMES if PROC_FS select SRCU + select PRINTK_NMI 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..8bc00476011d 100644 --- a/arch/x86/kernel/apic/hw_nmi.c +++ b/arch/x86/kernel/apic/hw_nmi.c @@ -30,40 +30,16 @@ u64 hw_nmi_get_sample_period(int watchdog_thresh) #ifdef arch_trigger_all_cpu_backtrace /* For reliability, we're prepared to waste bits here. */ 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; - int len; - int cpu; int i; int this_cpu = get_cpu(); - if (test_and_set_bit(0, &backtrace_flag)) { + if (0 != printk_nmi_prepare()) { /* - * 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; @@ -73,16 +49,6 @@ void arch_trigger_all_cpu_backtrace(bool include_self) 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", (include_self ? "all" : "other")); @@ -97,73 +63,20 @@ 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(); + printk_nmi_complete(); 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; - - cpu = smp_processor_id(); + int 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); + printk_nmi_this_cpu_begin(); printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu); show_regs(regs); - this_cpu_write(printk_func, printk_func_save); + printk_nmi_this_cpu_end(); cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); return NMI_HANDLED;
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 | 101 +++--------------------------------------- 2 files changed, 8 insertions(+), 94 deletions(-)