From patchwork Thu Jun 30 22:32:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Valentin Schneider X-Patchwork-Id: 586259 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C35D2C433EF for ; Thu, 30 Jun 2022 22:33:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231452AbiF3Wde (ORCPT ); Thu, 30 Jun 2022 18:33:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231467AbiF3WdQ (ORCPT ); Thu, 30 Jun 2022 18:33:16 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 816BFCC3 for ; Thu, 30 Jun 2022 15:33:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656628393; 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=P4I+MH1BitjShuNkM5CAAnuV26uY5raJYeW45VTPEJk=; b=JZtmmRxsXaNt8B1ln+kxGw8wTSS8jDzgLAURhvsCPsQGZ7oBMgy9KLUyQS+NzLyfq6CUBz 1ZEqbcrwFSI9Q1j+RfGTXG6JJ/ErUYCNOVT+lU0c0qeKUzK4ab8kwymBGX0rYzqVjAniYy PFYVSEI8pb35A+6gxPlXEDsCa3qy/ik= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-50-11ag8g_DPmmgHELh8eO70A-1; Thu, 30 Jun 2022 18:33:12 -0400 X-MC-Unique: 11ag8g_DPmmgHELh8eO70A-1 Received: by mail-wr1-f69.google.com with SMTP id j14-20020adfa54e000000b0021b8c8204easo60133wrb.0 for ; Thu, 30 Jun 2022 15:33:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=P4I+MH1BitjShuNkM5CAAnuV26uY5raJYeW45VTPEJk=; b=MQpDGVCfMxtLNej958YSerMuVLYAJWhnBCjndEMUxWnC5Jrg+xPdv1vYTpXzm6K9pr b6KexvUudOhgasqod+6oAaX4imQqWi405cU7qBLGxW4uGZ1BYe5PCW1ZCiKFRrEx1KAY JSrpTmYOXgeaIoikX1MQujY0eooc7arO06XL8UOnFgokvLml2jFXdCOHp9uoPZ9lSi4p OT2eQCQXy8E3txKVq2Q9QKveBgr2LLHi4ep8+GfGo3sqlmV0hRIndYQL3f9eIxzhFqO/ UkxGcmQw5Tk0iF8UCaP29g/UDRVwOpPH6Bmw7x0wz3QBHARjqyOYVD3mNl7xxgE6Lzj2 4w4w== X-Gm-Message-State: AJIora9JwAw5qbdu4m2E91jhRP0U3hoaEIBo2VwUKoOPZLqkKY/wOp5b hz8ZboF/nLflp/HxUMYQX7H4Zs6WLxY1fyZRhjgFWyiWqxm4tSCzz4mKmkmpbcXChsSbyOkpeMP +eYRcyitA73jHunL/ndhFENEq4Xg= X-Received: by 2002:a5d:5888:0:b0:21b:ccc1:ab00 with SMTP id n8-20020a5d5888000000b0021bccc1ab00mr10670848wrf.385.1656628391122; Thu, 30 Jun 2022 15:33:11 -0700 (PDT) X-Google-Smtp-Source: AGRyM1timqBDrx8wWmo3UJTVGb1qSoxfmdLn9yt/nE0BpLRCKzWRuI8/gHovtfTbzu2OliwBhtdqVA== X-Received: by 2002:a5d:5888:0:b0:21b:ccc1:ab00 with SMTP id n8-20020a5d5888000000b0021bccc1ab00mr10670828wrf.385.1656628390878; Thu, 30 Jun 2022 15:33:10 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id m9-20020a056000024900b0020c5253d907sm4308387wrz.83.2022.06.30.15.33.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jun 2022 15:33:10 -0700 (PDT) From: Valentin Schneider To: kexec@lists.infradead.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Eric Biederman , Arnd Bergmann , Petr Mladek , Miaohe Lin , Thomas Gleixner , Sebastian Andrzej Siewior , Juri Lelli , "Luis Claudio R. Goncalves" Subject: [PATCH v4 2/2] panic, kexec: Make __crash_kexec() NMI safe Date: Thu, 30 Jun 2022 23:32:58 +0100 Message-Id: <20220630223258.4144112-3-vschneid@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220630223258.4144112-1-vschneid@redhat.com> References: <20220630223258.4144112-1-vschneid@redhat.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org Attempting to get a crash dump out of a debug PREEMPT_RT kernel via an NMI panic() doesn't work. The cause of that lies in the PREEMPT_RT definition of mutex_trylock(): if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES) && WARN_ON_ONCE(!in_task())) return 0; This prevents an nmi_panic() from executing the main body of __crash_kexec() which does the actual kexec into the kdump kernel. The warning and return are explained by: 6ce47fd961fa ("rtmutex: Warn if trylock is called from hard/softirq context") [...] The reasons for this are: 1) There is a potential deadlock in the slowpath 2) Another cpu which blocks on the rtmutex will boost the task which allegedly locked the rtmutex, but that cannot work because the hard/softirq context borrows the task context. Furthermore, grabbing the lock isn't NMI safe, so do away with kexec_mutex and replace it with an atomic variable. This is somewhat overzealous as *some* callsites could keep using a mutex (e.g. the sysfs-facing ones like crash_shrink_memory()), but this has the benefit of involving a single unified lock and preventing any future NMI-related surprises. Tested by triggering NMI panics via: $ echo 1 > /proc/sys/kernel/panic_on_unrecovered_nmi $ echo 1 > /proc/sys/kernel/unknown_nmi_panic $ echo 1 > /proc/sys/kernel/panic $ ipmitool power diag Fixes: 6ce47fd961fa ("rtmutex: Warn if trylock is called from hard/softirq context") Signed-off-by: Valentin Schneider --- kernel/kexec.c | 11 ++++------- kernel/kexec_core.c | 20 ++++++++++---------- kernel/kexec_file.c | 4 ++-- kernel/kexec_internal.h | 15 ++++++++++++++- 4 files changed, 30 insertions(+), 20 deletions(-) diff --git a/kernel/kexec.c b/kernel/kexec.c index b5e40f069768..cb8e6e6f983c 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -93,13 +93,10 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments, /* * Because we write directly to the reserved memory region when loading - * crash kernels we need a mutex here to prevent multiple crash kernels - * from attempting to load simultaneously, and to prevent a crash kernel - * from loading over the top of a in use crash kernel. - * - * KISS: always take the mutex. + * crash kernels we need a serialization here to prevent multiple crash + * kernels from attempting to load simultaneously. */ - if (!mutex_trylock(&kexec_mutex)) + if (!kexec_trylock()) return -EBUSY; if (flags & KEXEC_ON_CRASH) { @@ -165,7 +162,7 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments, kimage_free(image); out_unlock: - mutex_unlock(&kexec_mutex); + kexec_unlock(); return ret; } diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 16370926b21a..b03859a0fbaa 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -46,7 +46,7 @@ #include #include "kexec_internal.h" -DEFINE_MUTEX(kexec_mutex); +atomic_t __kexec_lock = ATOMIC_INIT(0); /* Per cpu memory for storing cpu states in case of system crash. */ note_buf_t __percpu *crash_notes; @@ -964,7 +964,7 @@ late_initcall(kexec_core_sysctl_init); */ void __noclone __crash_kexec(struct pt_regs *regs) { - /* Take the kexec_mutex here to prevent sys_kexec_load + /* Take the kexec_lock here to prevent sys_kexec_load * running on one cpu from replacing the crash kernel * we are using after a panic on a different cpu. * @@ -972,7 +972,7 @@ void __noclone __crash_kexec(struct pt_regs *regs) * of memory the xchg(&kexec_crash_image) would be * sufficient. But since I reuse the memory... */ - if (mutex_trylock(&kexec_mutex)) { + if (kexec_trylock()) { if (kexec_crash_image) { struct pt_regs fixed_regs; @@ -981,7 +981,7 @@ void __noclone __crash_kexec(struct pt_regs *regs) machine_crash_shutdown(&fixed_regs); machine_kexec(kexec_crash_image); } - mutex_unlock(&kexec_mutex); + kexec_unlock(); } } STACK_FRAME_NON_STANDARD(__crash_kexec); @@ -1013,13 +1013,13 @@ ssize_t crash_get_memory_size(void) { ssize_t size = 0; - if (!mutex_trylock(&kexec_mutex)) + if (!kexec_trylock()) return -EBUSY; if (crashk_res.end != crashk_res.start) size = resource_size(&crashk_res); - mutex_unlock(&kexec_mutex); + kexec_unlock(); return size; } @@ -1039,7 +1039,7 @@ int crash_shrink_memory(unsigned long new_size) unsigned long old_size; struct resource *ram_res; - if (!mutex_trylock(&kexec_mutex)) + if (!kexec_trylock()) return -EBUSY; if (kexec_crash_image) { @@ -1078,7 +1078,7 @@ int crash_shrink_memory(unsigned long new_size) insert_resource(&iomem_resource, ram_res); unlock: - mutex_unlock(&kexec_mutex); + kexec_unlock(); return ret; } @@ -1150,7 +1150,7 @@ int kernel_kexec(void) { int error = 0; - if (!mutex_trylock(&kexec_mutex)) + if (!kexec_trylock()) return -EBUSY; if (!kexec_image) { error = -EINVAL; @@ -1226,7 +1226,7 @@ int kernel_kexec(void) #endif Unlock: - mutex_unlock(&kexec_mutex); + kexec_unlock(); return error; } diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index 145321a5e798..42b95bf58daf 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -334,7 +334,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd, image = NULL; - if (!mutex_trylock(&kexec_mutex)) + if (!kexec_trylock()) return -EBUSY; dest_image = &kexec_image; @@ -406,7 +406,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd, if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image) arch_kexec_protect_crashkres(); - mutex_unlock(&kexec_mutex); + kexec_unlock(); kimage_free(image); return ret; } diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h index 48aaf2ac0d0d..74da1409cd14 100644 --- a/kernel/kexec_internal.h +++ b/kernel/kexec_internal.h @@ -13,7 +13,20 @@ void kimage_terminate(struct kimage *image); int kimage_is_destination_range(struct kimage *image, unsigned long start, unsigned long end); -extern struct mutex kexec_mutex; +/* + * Whatever is used to serialize accesses to the kexec_crash_image needs to be + * NMI safe, as __crash_kexec() can happen during nmi_panic(), so here we use a + * "simple" atomic variable that is acquired with a cmpxchg(). + */ +extern atomic_t __kexec_lock; +static inline bool kexec_trylock(void) +{ + return atomic_cmpxchg_acquire(&__kexec_lock, 0, 1) == 0; +} +static inline void kexec_unlock(void) +{ + atomic_set_release(&__kexec_lock, 0); +} #ifdef CONFIG_KEXEC_FILE #include