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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3185C77B76 for ; Tue, 18 Apr 2023 12:37:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231745AbjDRMhc (ORCPT ); Tue, 18 Apr 2023 08:37:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231764AbjDRMh3 (ORCPT ); Tue, 18 Apr 2023 08:37:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B749F658C for ; Tue, 18 Apr 2023 05:37:26 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 55D46632B3 for ; Tue, 18 Apr 2023 12:37:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3C1EAC433EF; Tue, 18 Apr 2023 12:37:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1681821445; bh=5op9BPLFe+PJyBhjHnYYX1TwMbzgrAgackaqGVX0eJ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Fr5pLrTDzE0mS0XZo0pocnxPVIKnBamX7a1UOmBUOOT/J9+mM71vVa0/bHlsmu0MS tl3N514Dd3jh1yhGoD49AbVl7r4D3hLWc10Jls/1lndVXNpmzqFlL3dhFsJWDk8Tjn HPneFT/d9oHV4vVH59V46KB224WL1g/4c/EChjaI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Valentin Schneider , Arnd Bergmann , "Eric W . Biederman" , Juri Lelli , "Luis Claudio R. Goncalves" , Miaohe Lin , Petr Mladek , Sebastian Andrzej Siewior , Thomas Gleixner , Baoquan He , Andrew Morton , Wen Yang Subject: [PATCH 5.10 122/124] kexec: turn all kexec_mutex acquisitions into trylocks Date: Tue, 18 Apr 2023 14:22:21 +0200 Message-Id: <20230418120314.188444872@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230418120309.539243408@linuxfoundation.org> References: <20230418120309.539243408@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Valentin Schneider commit 7bb5da0d490b2d836c5218f5186ee588d2145310 upstream. Patch series "kexec, panic: Making crash_kexec() NMI safe", v4. This patch (of 2): 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 have 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. Link: https://lkml.kernel.org/r/20220630223258.4144112-1-vschneid@redhat.com Link: https://lkml.kernel.org/r/20220630223258.4144112-2-vschneid@redhat.com Signed-off-by: Valentin Schneider Cc: Arnd Bergmann Cc: "Eric W . Biederman" Cc: Juri Lelli Cc: Luis Claudio R. Goncalves Cc: Miaohe Lin Cc: Petr Mladek Cc: Sebastian Andrzej Siewior Cc: Thomas Gleixner Cc: Baoquan He Signed-off-by: Andrew Morton Signed-off-by: Wen Yang Signed-off-by: Greg Kroah-Hartman --- include/linux/kexec.h | 2 +- kernel/kexec_core.c | 12 ++++++++---- kernel/ksysfs.c | 7 ++++++- 3 files changed, 15 insertions(+), 6 deletions(-) --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -380,8 +380,8 @@ extern note_buf_t __percpu *crash_notes; extern bool kexec_in_progress; int crash_shrink_memory(unsigned long new_size); -size_t crash_get_memory_size(void); void crash_free_reserved_phys_range(unsigned long begin, unsigned long end); +ssize_t crash_get_memory_size(void); void arch_kexec_protect_crashkres(void); void arch_kexec_unprotect_crashkres(void); --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -989,13 +989,16 @@ 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; } @@ -1016,7 +1019,8 @@ int crash_shrink_memory(unsigned long ne 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; --- a/kernel/ksysfs.c +++ b/kernel/ksysfs.c @@ -106,7 +106,12 @@ 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,