From patchwork Tue Feb 3 19:06:55 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Thompson X-Patchwork-Id: 5771341 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 678EEBF440 for ; Tue, 3 Feb 2015 19:13:10 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 4C2A020212 for ; Tue, 3 Feb 2015 19:13:09 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3C64F201FB for ; Tue, 3 Feb 2015 19:13:08 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1YIisY-0003SL-Ob; Tue, 03 Feb 2015 19:11:18 +0000 Received: from mail-wi0-f176.google.com ([209.85.212.176]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1YIisB-0002yO-KE for linux-arm-kernel@lists.infradead.org; Tue, 03 Feb 2015 19:10:56 +0000 Received: by mail-wi0-f176.google.com with SMTP id bs8so26869099wib.3 for ; Tue, 03 Feb 2015 11:10:33 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=tcmKhX02c3dOn4V6QY2svjqIwGJAhJseazomqfUjLeA=; b=A8bbLQWTLrmX0JZNWh4op+axzxB2HfQhijanrap8YW5PyaZA5kSWMbwwIoCEdCo/4X fLVSje/uv6C1elVhcJmPhvcx64fwnkqOyPXUa093AxOmdIejN6OLWzWBbB61uwDtncWB i8qRTkyTin4aPNJA9Id8M4D9v71b+9rvaIDzpI/qQzYm46ZYlBEWOmKDrd2+104rwxEi q7WrowVrG936OoApKBecVst+wXYD4t7XWkhxDlWyIKLtkhvL221wrBUhHYoBR3f8VJg+ ya/0TiTUPCb4df2NV27Gh8l2hu4I3FN6Ii3+Xr8UBaYsYVoFNS1bCxRsBUC7DrZ1ghQS Qwbg== X-Gm-Message-State: ALoCoQlx/nk+bjfM3ZTJYPuN3+lC7Dd1aE1UNL0rH+LirRb/khC69YWiPkopbd8OvJfXuyZ9E0Sn X-Received: by 10.195.13.168 with SMTP id ez8mr17396074wjd.30.1422990633864; Tue, 03 Feb 2015 11:10:33 -0800 (PST) Received: from sundance.lan (cpc4-aztw19-0-0-cust157.18-1.cable.virginm.net. [82.33.25.158]) by mx.google.com with ESMTPSA id bi9sm12603663wib.18.2015.02.03.11.10.31 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Feb 2015 11:10:32 -0800 (PST) From: Daniel Thompson To: Thomas Gleixner Subject: [PATCH 3.19-rc6 v16 4/6] printk: Simple implementation for NMI backtracing Date: Tue, 3 Feb 2015 19:06:55 +0000 Message-Id: <1422990417-1783-5-git-send-email-daniel.thompson@linaro.org> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1422990417-1783-1-git-send-email-daniel.thompson@linaro.org> References: <1422022952-31552-1-git-send-email-daniel.thompson@linaro.org> <1422990417-1783-1-git-send-email-daniel.thompson@linaro.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20150203_111055_977527_77A3585D X-CRM114-Status: GOOD ( 28.12 ) X-Spam-Score: -0.7 (/) Cc: Daniel Thompson , linaro-kernel@lists.linaro.org, Russell King , Jason Cooper , patches@linaro.org, Marc Zyngier , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Steven Rostedt , Sumit Semwal , Dmitry Pervushin , Dirk Behme , John Stultz , Tim Sander , Daniel Drake , Stephen Boyd , linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently there is a quite a pile of code sitting in arch/x86/kernel/apic/hw_nmi.c to support safe all-cpu backtracing from NMI. The code is inaccessible to backtrace implementations for other architectures, which is a shame because they would probably like to be safe too. Copy this code into printk. We'll port the x86 NMI backtrace to it in a later patch. Incidentally, technically I think it might be safe to call printk_nmi_prepare() from NMI, providing care were taken to honour the return code. printk_nmi_complete() cannot be called from NMI but could be scheduled using irq_work_queue(). However honouring the return code means sometimes it is impossible to get the message out so in most cases I'd say using this code in such a way should probably attract sympathy and/or derision rather than admiration. Signed-off-by: Daniel Thompson Cc: Steven Rostedt --- include/linux/printk.h | 18 ++++++ init/Kconfig | 3 + kernel/printk/printk.c | 149 +++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 170 insertions(+) diff --git a/include/linux/printk.h b/include/linux/printk.h index c8f170324e64..03c6921b3fcd 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -219,6 +219,24 @@ static inline void show_regs_print_info(const char *log_lvl) } #endif +#ifdef CONFIG_PRINTK_NMI +/* + * printk_nmi_prepare/complete are called to prepare the system for + * some or all cores to issue trace from NMI. printk_nmi_complete will + * print buffered output and cannot (safely) be called from NMI. + */ +extern int printk_nmi_prepare(void); +extern void printk_nmi_complete(void); + +/* + * printk_nmi_this_cpu_begin/end are used divert/restore printk on this + * cpu. The result is the output of printk() (by this CPU) will be + * stored in temporary buffers for later printing by printk_nmi_complete. + */ +extern void printk_nmi_this_cpu_begin(void); +extern void printk_nmi_this_cpu_end(void); +#endif + extern asmlinkage void dump_stack(void) __cold; #ifndef pr_fmt diff --git a/init/Kconfig b/init/Kconfig index 9afb971497f4..13b843e3b5f4 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1430,6 +1430,9 @@ config PRINTK very difficult to diagnose system problems, saying N here is strongly discouraged. +config PRINTK_NMI + bool + config BUG bool "BUG() support" if EXPERT default y diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 02d6b6d28796..fe1cd57ea349 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1829,6 +1829,155 @@ EXPORT_SYMBOL_GPL(vprintk_default); */ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; +#ifdef CONFIG_PRINTK_NMI + +#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); + +static DEFINE_PER_CPU(printk_func_t, nmi_print_saved_print_func); + +/* "in progress" flag of NMI printing */ +static unsigned long nmi_print_flag; + +static int __init printk_nmi_init(void) +{ + struct nmi_seq_buf *s; + int cpu; + + for_each_possible_cpu(cpu) { + s = &per_cpu(nmi_print_seq, cpu); + seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE); + } + + return 0; +} +pure_initcall(printk_nmi_init); + +/* + * 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. + * + * This is not a generic printk() implementation and must be used with + * great care. In particular there is a static limit on the quantity of + * data that may be emitted during NMI, only one client can be active at + * one time (arbitrated by the return value of printk_nmi_begin() and + * it is required that something at task or interrupt context be scheduled + * to issue the output. + */ +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; +} + +/* + * Reserve the NMI printk mechanism. Return an error if some other component + * is already using it. + */ +int printk_nmi_prepare(void) +{ + if (test_and_set_bit(0, &nmi_print_flag)) { + /* + * If something is already using the NMI print facility we + * can't allow a second one... + */ + return -EBUSY; + } + + return 0; +} + +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 printk_nmi_complete(void) +{ + struct nmi_seq_buf *s; + int len, cpu, i, last_i; + + /* + * Now that all the NMIs have triggered, we can dump out their + * back traces safely to the console. + */ + for_each_possible_cpu(cpu) { + s = &per_cpu(nmi_print_seq, cpu); + last_i = 0; + + 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"); + } + + /* Wipe out the buffer ready for the next time around. */ + seq_buf_clear(&s->seq); + } + + clear_bit(0, &nmi_print_flag); + smp_mb__after_atomic(); +} + +void printk_nmi_this_cpu_begin(void) +{ + /* + * Detect double-begins and report them. This code is unsafe (because + * it will print from NMI) but things are pretty badly damaged if the + * NMI re-enters and is somehow granted permission to use NMI printk, + * so how much worse can it get? Also since this code interferes with + * the operation of printk it is unlikely that any consequential + * failures will be able to log anything making this our last + * opportunity to tell anyone that something is wrong. + */ + if (this_cpu_read(nmi_print_saved_print_func)) { + this_cpu_write(printk_func, vprintk_default); + BUG(); + } + + this_cpu_write(nmi_print_saved_print_func, this_cpu_read(printk_func)); + this_cpu_write(printk_func, nmi_vprintk); +} + +void printk_nmi_this_cpu_end(void) +{ + this_cpu_write(printk_func, this_cpu_read(nmi_print_saved_print_func)); + this_cpu_write(nmi_print_saved_print_func, NULL); +} + +#endif /* CONFIG_PRINTK_NMI */ + /** * printk - print a kernel message * @fmt: format string