From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F321C4332E for ; Tue, 16 Mar 2021 23:34:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E15B64F0F for ; Tue, 16 Mar 2021 23:34:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229821AbhCPXdu (ORCPT ); Tue, 16 Mar 2021 19:33:50 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:45360 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229769AbhCPXd3 (ORCPT ); Tue, 16 Mar 2021 19:33:29 -0400 From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1615937608; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DPEbS8EENZd+6UxIQP+0wBMd5xtfR6sjyg6AAKLVwXo=; b=h9QsPno5Vo/XanI8eiIoM4TeZMNULvO8A7WVWE1Tbpog5WJWGePgJckW2jf+fb+V4f4PZD fFY0KO2ZnwQnxEmOKzHxAzq6iST82HTjQy2Tr5DlYK61jYdLd42hN/lxQiV+c+72ynNLH6 9B+hsw/F23WAvoOzNCrlTSuGPSABptoxr/2B/lcZ9gdozBOLkF5ZRfRf9Se5eaW70aj62o 7oIgUwakcQWL3woaxLNvPEHN3yb0R//v3fLCHDCC1+MQ4qWrNQAmLHdSpH1s6rDUOYkFcn nnaIYz37WQ5MQr8TIXZXHZm970lwor4TcHghWH1Rgj023mhCaYH+qeGwt7HRYw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1615937608; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DPEbS8EENZd+6UxIQP+0wBMd5xtfR6sjyg6AAKLVwXo=; b=NI68i/PlYoZl7UuqWa6T+TC23JHnpQ1Ob7daIv2Ld+yoGYEafHBB4ak8uAmi1IPy3cD5ZC 6Q9qSP6sS4/PXcCA== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH next v1 1/3] printk: track/limit recursion Date: Wed, 17 Mar 2021 00:33:24 +0100 Message-Id: <20210316233326.10778-2-john.ogness@linutronix.de> In-Reply-To: <20210316233326.10778-1-john.ogness@linutronix.de> References: <20210316233326.10778-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Track printk() recursion and limit it to 3 levels per-CPU and per-context. Signed-off-by: John Ogness --- kernel/printk/printk.c | 80 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 77 insertions(+), 3 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 2f829fbf0a13..c666e3e43f0c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1940,6 +1940,71 @@ static void call_console_drivers(const char *ext_text, size_t ext_len, } } +/* + * Recursion is tracked separately on each CPU. If NMIs are supported, an + * additional NMI context per CPU is also separately tracked. Until per-CPU + * is available, a separate "early tracking" is performed. + */ +#ifdef CONFIG_PRINTK_NMI +#define PRINTK_CTX_NUM 2 +#else +#define PRINTK_CTX_NUM 1 +#endif +static DEFINE_PER_CPU(char [PRINTK_CTX_NUM], printk_count); +static char printk_count_early[PRINTK_CTX_NUM]; + +/* + * Recursion is limited to keep the output sane. printk() should not require + * more than 1 level of recursion (allowing, for example, printk() to trigger + * a WARN), but a higher value is used in case some printk-internal errors + * exist, such as the ringbuffer validation checks failing. + */ +#define PRINTK_MAX_RECURSION 3 + +/* Return a pointer to the dedicated counter for the CPU+context of the caller. */ +static char *printk_recursion_counter(void) +{ + int ctx = 0; + +#ifdef CONFIG_PRINTK_NMI + if (in_nmi()) + ctx = 1; +#endif + if (!printk_percpu_data_ready()) + return &printk_count_early[ctx]; + return &((*this_cpu_ptr(&printk_count))[ctx]); +} + +/* + * Enter recursion tracking. Interrupts are disabled to simplify tracking. + * The caller must check the return value to see if the recursion is allowed. + * On failure, interrupts are not disabled. + */ +static bool printk_enter_irqsave(unsigned long *flags) +{ + char *count; + + local_irq_save(*flags); + count = printk_recursion_counter(); + if (*count > PRINTK_MAX_RECURSION) { + local_irq_restore(*flags); + return false; + } + (*count)++; + + return true; +} + +/* Exit recursion tracking, restoring interrupts. */ +static void printk_exit_irqrestore(unsigned long flags) +{ + char *count; + + count = printk_recursion_counter(); + (*count)--; + local_irq_restore(flags); +} + int printk_delay_msec __read_mostly; static inline void printk_delay(void) @@ -2040,11 +2105,13 @@ int vprintk_store(int facility, int level, struct prb_reserved_entry e; enum log_flags lflags = 0; struct printk_record r; + unsigned long irqflags; u16 trunc_msg_len = 0; char prefix_buf[8]; u16 reserve_size; va_list args2; u16 text_len; + int ret = 0; u64 ts_nsec; /* @@ -2055,6 +2122,9 @@ int vprintk_store(int facility, int level, */ ts_nsec = local_clock(); + if (!printk_enter_irqsave(&irqflags)) + return 0; + /* * The sprintf needs to come first since the syslog prefix might be * passed in as a parameter. An extra byte must be reserved so that @@ -2092,7 +2162,8 @@ int vprintk_store(int facility, int level, prb_commit(&e); } - return text_len; + ret = text_len; + goto out; } } @@ -2108,7 +2179,7 @@ int vprintk_store(int facility, int level, prb_rec_init_wr(&r, reserve_size + trunc_msg_len); if (!prb_reserve(&e, prb, &r)) - return 0; + goto out; } /* fill message */ @@ -2130,7 +2201,10 @@ int vprintk_store(int facility, int level, else prb_final_commit(&e); - return (text_len + trunc_msg_len); + ret = text_len + trunc_msg_len; +out: + printk_exit_irqrestore(irqflags); + return ret; } asmlinkage int vprintk_emit(int facility, int level, -- 2.20.1