Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933083AbbLSKPZ (ORCPT ); Sat, 19 Dec 2015 05:15:25 -0500 Received: from terminus.zytor.com ([198.137.202.10]:36557 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932258AbbLSKOZ (ORCPT ); Sat, 19 Dec 2015 05:14:25 -0500 Date: Sat, 19 Dec 2015 02:13:21 -0800 From: tip-bot for Hidehiro Kawai Message-ID: Cc: d.hatayama@jp.fujitsu.com, linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com, tglx@linutronix.de, bhe@redhat.com, mhocko@suse.com, sjenning@redhat.com, vgoyal@redhat.com, mnfhuang@gmail.com, hpa@zytor.com, peterz@infradead.org, vkuznets@redhat.com, mingo@kernel.org, bp@suse.de, x86@kernel.org, hidehiro.kawai.ez@hitachi.com, ebiederm@xmission.com, dyoung@redhat.com, masami.hiramatsu.pt@hitachi.com, corbet@lwn.net, akpm@linux-foundation.org, rostedt@goodmis.org Reply-To: tglx@linutronix.de, bhe@redhat.com, d.hatayama@jp.fujitsu.com, schwidefsky@de.ibm.com, linux-kernel@vger.kernel.org, hpa@zytor.com, mnfhuang@gmail.com, vkuznets@redhat.com, peterz@infradead.org, mhocko@suse.com, vgoyal@redhat.com, sjenning@redhat.com, bp@suse.de, x86@kernel.org, mingo@kernel.org, masami.hiramatsu.pt@hitachi.com, corbet@lwn.net, akpm@linux-foundation.org, rostedt@goodmis.org, hidehiro.kawai.ez@hitachi.com, dyoung@redhat.com, ebiederm@xmission.com In-Reply-To: <20151210014630.25437.94161.stgit@softrs> References: <20151210014630.25437.94161.stgit@softrs> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/apic] kexec: Fix race between panic() and crash_kexec() Git-Commit-ID: 7bbee5ca3896f69f09c68be549cb8997abe6bca6 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6050 Lines: 180 Commit-ID: 7bbee5ca3896f69f09c68be549cb8997abe6bca6 Gitweb: http://git.kernel.org/tip/7bbee5ca3896f69f09c68be549cb8997abe6bca6 Author: Hidehiro Kawai AuthorDate: Mon, 14 Dec 2015 11:19:11 +0100 Committer: Thomas Gleixner CommitDate: Sat, 19 Dec 2015 11:07:01 +0100 kexec: Fix race between panic() and crash_kexec() Currently, panic() and crash_kexec() can be called at the same time. For example (x86 case): CPU 0: oops_end() crash_kexec() mutex_trylock() // acquired nmi_shootdown_cpus() // stop other CPUs CPU 1: panic() crash_kexec() mutex_trylock() // failed to acquire smp_send_stop() // stop other CPUs infinite loop If CPU 1 calls smp_send_stop() before nmi_shootdown_cpus(), kdump fails. In another case: CPU 0: oops_end() crash_kexec() mutex_trylock() // acquired io_check_error() panic() crash_kexec() mutex_trylock() // failed to acquire infinite loop Clearly, this is an undesirable result. To fix this problem, this patch changes crash_kexec() to exclude others by using the panic_cpu atomic. Signed-off-by: Hidehiro Kawai Acked-by: Michal Hocko Cc: Andrew Morton Cc: Baoquan He Cc: Dave Young Cc: "Eric W. Biederman" Cc: HATAYAMA Daisuke Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jonathan Corbet Cc: kexec@lists.infradead.org Cc: linux-doc@vger.kernel.org Cc: Martin Schwidefsky Cc: Masami Hiramatsu Cc: Minfei Huang Cc: Peter Zijlstra Cc: Seth Jennings Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Vitaly Kuznetsov Cc: Vivek Goyal Cc: x86-ml Link: http://lkml.kernel.org/r/20151210014630.25437.94161.stgit@softrs Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner --- include/linux/kexec.h | 2 ++ kernel/kexec_core.c | 30 +++++++++++++++++++++++++++++- kernel/panic.c | 8 ++++++-- 3 files changed, 37 insertions(+), 3 deletions(-) diff --git a/include/linux/kexec.h b/include/linux/kexec.h index d140b1e..7b68d27 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -237,6 +237,7 @@ extern int kexec_purgatory_get_set_symbol(struct kimage *image, unsigned int size, bool get_value); extern void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name); +extern void __crash_kexec(struct pt_regs *); extern void crash_kexec(struct pt_regs *); int kexec_should_crash(struct task_struct *); void crash_save_cpu(struct pt_regs *regs, int cpu); @@ -332,6 +333,7 @@ int __weak arch_kexec_apply_relocations(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, #else /* !CONFIG_KEXEC_CORE */ struct pt_regs; struct task_struct; +static inline void __crash_kexec(struct pt_regs *regs) { } static inline void crash_kexec(struct pt_regs *regs) { } static inline int kexec_should_crash(struct task_struct *p) { return 0; } #define kexec_in_progress false diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 11b64a6..c823f30 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -853,7 +853,12 @@ struct kimage *kexec_image; struct kimage *kexec_crash_image; int kexec_load_disabled; -void crash_kexec(struct pt_regs *regs) +/* + * No panic_cpu check version of crash_kexec(). This function is called + * only when panic_cpu holds the current CPU number; this is the only CPU + * which processes crash_kexec routines. + */ +void __crash_kexec(struct pt_regs *regs) { /* Take the kexec_mutex here to prevent sys_kexec_load * running on one cpu from replacing the crash kernel @@ -876,6 +881,29 @@ void crash_kexec(struct pt_regs *regs) } } +void crash_kexec(struct pt_regs *regs) +{ + int old_cpu, this_cpu; + + /* + * Only one CPU is allowed to execute the crash_kexec() code as with + * panic(). Otherwise parallel calls of panic() and crash_kexec() + * may stop each other. To exclude them, we use panic_cpu here too. + */ + this_cpu = raw_smp_processor_id(); + old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); + if (old_cpu == PANIC_CPU_INVALID) { + /* This is the 1st CPU which comes here, so go ahead. */ + __crash_kexec(regs); + + /* + * Reset panic_cpu to allow another panic()/crash_kexec() + * call. + */ + atomic_set(&panic_cpu, PANIC_CPU_INVALID); + } +} + size_t crash_get_memory_size(void) { size_t size = 0; diff --git a/kernel/panic.c b/kernel/panic.c index 06f31b49..b333380 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -136,9 +136,11 @@ void panic(const char *fmt, ...) * everything else. * If we want to run this after calling panic_notifiers, pass * the "crash_kexec_post_notifiers" option to the kernel. + * + * Bypass the panic_cpu check and call __crash_kexec directly. */ if (!crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); /* * Note smp_send_stop is the usual smp shutdown function, which @@ -161,9 +163,11 @@ void panic(const char *fmt, ...) * panic_notifiers and dumping kmsg before kdump. * Note: since some panic_notifiers can make crashed kernel * more unstable, it can increase risks of the kdump failure too. + * + * Bypass the panic_cpu check and call __crash_kexec directly. */ if (crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); bust_spinlocks(0); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/