[1/3] nmi: create generic NMI backtrace implementation

Message ID	E1ZFTSm-0006uz-3s@rmk-PC.arm.linux.org.uk (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org> In-Reply-To: <20150715203911.GF7557@n2100.arm.linux.org.uk> References: <20150715203911.GF7557@n2100.arm.linux.org.uk> From: Russell King <rmk+kernel@arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org,x86@kernel.org Subject: [PATCH 1/3] nmi: create generic NMI backtrace implementation MIME-Version: 1.0 Content-Disposition: inline Message-Id: <E1ZFTSm-0006uz-3s@rmk-PC.arm.linux.org.uk> Date: Wed, 15 Jul 2015 21:39:32 +0100 Precedence: list Cc: Daniel Thompson <daniel.thompson@linaro.org>, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" <linux-arm-kernel-bounces@lists.infradead.org> Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org

diff --git a/include/linux/nmi.h b/include/linux/nmi.h index f94da0e65dea..5791e3229068 100644 --- a/include/linux/nmi.h +++ b/include/linux/nmi.h @@ -49,6 +49,12 @@ static inline bool trigger_allbutself_cpu_backtrace(void) arch_trigger_all_cpu_backtrace(false); return true; } + +/* generic implementation */ +void nmi_trigger_all_cpu_backtrace(bool include_self, + void (*raise)(cpumask_t *mask)); +bool nmi_cpu_backtrace(struct pt_regs *regs); + #else static inline bool trigger_all_cpu_backtrace(void) { diff --git a/lib/Makefile b/lib/Makefile index 6897b527581a..392169c5bc4e 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -13,7 +13,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \ sha1.o md5.o irq_regs.o argv_split.o \ proportions.o flex_proportions.o ratelimit.o show_mem.o \ is_single_threaded.o plist.o decompress.o kobject_uevent.o \ - earlycpio.o seq_buf.o + earlycpio.o seq_buf.o nmi_backtrace.o obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o lib-$(CONFIG_MMU) += ioremap.o diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c new file mode 100644 index 000000000000..88d3d32e5923 --- /dev/null +++ b/lib/nmi_backtrace.c @@ -0,0 +1,162 @@ +/* + * NMI backtrace support + * + * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King, + * with the following header: + * + * HW NMI watchdog support + * + * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc. + * + * Arch specific calls to support NMI watchdog + * + * Bits copied from original nmi.c file + */ +#include <linux/cpumask.h> +#include <linux/delay.h> +#include <linux/kprobes.h> +#include <linux/nmi.h> +#include <linux/seq_buf.h> + +#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 nmi_trigger_all_cpu_backtrace(bool include_self, + void (*raise)(cpumask_t *mask)) +{ + struct nmi_seq_buf *s; + int i, cpu, this_cpu = get_cpu(); + + if (test_and_set_bit(0, &backtrace_flag)) { + /* + * If there is already a trigger_all_cpu_backtrace() in progress + * (backtrace_flag == 1), don't output double cpu dump infos. + */ + 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", + (include_self ? "all" : "other")); + raise(to_cpumask(backtrace_mask)); + } + + /* Wait for up to 10 seconds for all CPUs to do the backtrace */ + for (i = 0; i < 10 * 1000; i++) { + if (cpumask_empty(to_cpumask(backtrace_mask))) + break; + mdelay(1); + 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 len, 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(); + 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; +} + +bool nmi_cpu_backtrace(struct pt_regs *regs) +{ + 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); + pr_warn("NMI backtrace for cpu %d\n", cpu); + show_regs(regs); + this_cpu_write(printk_func, printk_func_save); + + cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); + return true; + } + + return false; +} +NOKPROBE_SYMBOL(nmi_cpu_backtrace); +#endif

[1/3] nmi: create generic NMI backtrace implementation

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