From patchwork Thu Jun 30 17:20:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Valentin Schneider X-Patchwork-Id: 587048 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 D5879C43334 for ; Thu, 30 Jun 2022 17:21:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235814AbiF3RVU (ORCPT ); Thu, 30 Jun 2022 13:21:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46154 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235411AbiF3RVT (ORCPT ); Thu, 30 Jun 2022 13:21:19 -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 744DD1C13C for ; Thu, 30 Jun 2022 10:21:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656609677; 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=M7KwLoH0d9jahqdN5gAGjp/0Ed77DbKf9u/QbOUdSiM=; b=XdeDthHerYLKGWeYE8nDMyM2vHDfRk7SslNjHGeVuqMTqPuSZ2f5xM0WrMMuHSO3GnSNV/ 07kwTgPYpwbT8XYDTCvSzR+fmSVJL/4CAIK39Mi1wTkPtgQfPv+1upjKu7EQeFUASzirL2 LqI4qj/4XRk+Q7/e3b6OVQgI8s0qazo= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-674-9siM450MO26f7CX4TlxeXw-1; Thu, 30 Jun 2022 13:21:16 -0400 X-MC-Unique: 9siM450MO26f7CX4TlxeXw-1 Received: by mail-wm1-f71.google.com with SMTP id be12-20020a05600c1e8c00b0039c506b52a4so1659765wmb.1 for ; Thu, 30 Jun 2022 10:21:16 -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=M7KwLoH0d9jahqdN5gAGjp/0Ed77DbKf9u/QbOUdSiM=; b=ramPE5DraauPI1f2zl7s7e9J32F79PF7FvKkAVs964Pa7welp1wVw/m8D/XgJNKd4d PE1cjXsDfGCeBPF91MV5e9ZoyAvSpttJhJlWFFv5IpIVT2ksZMyIW1vQ40AAq7Bbb5YD Z39kWjr4JSqJ+VVeFiZ4ckTtu+/FV1gJvg88RHvR7N8YZj7Ml8k9KfkW9aC3WG9VcHF/ bKFL3Pj6pYRaxXdyltDh8kovXl1dgHtr+VN7YaTBQK/IU7f9rTUiI1PC+KZAcpHUXXqE DzDcPMCPaQD0BnGmXbWWR7m6bcDiNgzRhydeDaPlAy7DYHoSOsn9kaFeYAoY82qyuWea rwLw== X-Gm-Message-State: AJIora9VrE7JYg5qBZT9IChKCrPRlnJXlHuIVa7LKZEzY8IBDZlsHhgJ lEeUZZ1lVFUiz9LG1BqOmfVlf+OXl7KkUGknCqgpVt/L15pH/oMcsrfv9lQKwOgJYl7T3/b+2Jm SoTl5AgwMu9Gvqof3BtU0yKNiQ7I= X-Received: by 2002:a5d:5d89:0:b0:21d:407a:d8d3 with SMTP id ci9-20020a5d5d89000000b0021d407ad8d3mr2670458wrb.369.1656609674407; Thu, 30 Jun 2022 10:21:14 -0700 (PDT) X-Google-Smtp-Source: AGRyM1uokbBJS0X9zNHyARJlxgnxT5Y/QOC+ZqoAr8T+We19KOdP9D4fgQBmv32oBqxEO1suOpVFfg== X-Received: by 2002:a5d:5d89:0:b0:21d:407a:d8d3 with SMTP id ci9-20020a5d5d89000000b0021d407ad8d3mr2670436wrb.369.1656609674232; Thu, 30 Jun 2022 10:21:14 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id f20-20020a05600c155400b0039c41686421sm4065122wmg.17.2022.06.30.10.21.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jun 2022 10:21:13 -0700 (PDT) From: Valentin Schneider To: kexec@lists.infradead.org, linux-rt-users@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 v3 1/2] kexec: Turn all kexec_mutex acquisitions into trylocks Date: Thu, 30 Jun 2022 18:20:40 +0100 Message-Id: <20220630172041.4100123-2-vschneid@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220630172041.4100123-1-vschneid@redhat.com> References: <20220630172041.4100123-1-vschneid@redhat.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org Most acquistions of kexec_mutex are done via mutex_trylock() - those were a direct "translation" from: 8c5a1cf0ad3a ("kexec: use a mutex for locking rather than xchg()") there has however been two additions since then that use mutex_lock(): crash_get_memory_size() and crash_shrink_memory(). A later commit will replace said mutex with an atomic variable, and locking operations will become atomic_cmpxchg(). Rather than having those mutex_lock() become while (atomic_cmpxchg(&lock, 0, 1)), turn them into trylocks that can return -EBUSY on acquisition failure. This does halve the printable size of the crash kernel, but that's still neighbouring 2G for 32bit kernels which should be ample enough. Signed-off-by: Valentin Schneider --- include/linux/kexec.h | 2 +- kernel/kexec_core.c | 12 ++++++++---- kernel/ksysfs.c | 7 ++++++- 3 files changed, 15 insertions(+), 6 deletions(-) diff --git a/include/linux/kexec.h b/include/linux/kexec.h index ce6536f1d269..54d7030d3c41 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -390,7 +390,7 @@ extern int kexec_load_disabled; extern bool kexec_in_progress; int crash_shrink_memory(unsigned long new_size); -size_t crash_get_memory_size(void); +ssize_t crash_get_memory_size(void); void crash_free_reserved_phys_range(unsigned long begin, unsigned long end); void arch_kexec_protect_crashkres(void); diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 4d34c78334ce..16370926b21a 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -1009,13 +1009,16 @@ void crash_kexec(struct pt_regs *regs) } } -size_t crash_get_memory_size(void) +ssize_t crash_get_memory_size(void) { - size_t size = 0; + ssize_t size = 0; + + if (!mutex_trylock(&kexec_mutex)) + return -EBUSY; - mutex_lock(&kexec_mutex); if (crashk_res.end != crashk_res.start) size = resource_size(&crashk_res); + mutex_unlock(&kexec_mutex); return size; } @@ -1036,7 +1039,8 @@ int crash_shrink_memory(unsigned long new_size) unsigned long old_size; struct resource *ram_res; - mutex_lock(&kexec_mutex); + if (!mutex_trylock(&kexec_mutex)) + return -EBUSY; if (kexec_crash_image) { ret = -ENOENT; diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c index b1292a57c2a5..65dba9076f31 100644 --- a/kernel/ksysfs.c +++ b/kernel/ksysfs.c @@ -105,7 +105,12 @@ KERNEL_ATTR_RO(kexec_crash_loaded); static ssize_t kexec_crash_size_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { - return sprintf(buf, "%zu\n", crash_get_memory_size()); + ssize_t size = crash_get_memory_size(); + + if (size < 0) + return size; + + return sprintf(buf, "%zd\n", size); } static ssize_t kexec_crash_size_store(struct kobject *kobj, struct kobj_attribute *attr,