Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754105AbbLJBtb (ORCPT ); Wed, 9 Dec 2015 20:49:31 -0500 Received: from mail7.hitachi.co.jp ([133.145.228.42]:42237 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751572AbbLJBtV (ORCPT ); Wed, 9 Dec 2015 20:49:21 -0500 X-AuditID: 85900ec0-9ebcbb9000001a57-d3-5668da1c1c8f X-Mailbox-Line: From nobody Thu Dec 10 10:46:32 2015 Subject: [V6 PATCH 3/6] kexec: Fix race between panic() and crash_kexec() called directly To: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal From: Hidehiro Kawai Cc: Baoquan He , linux-doc@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt , Michal Hocko , Borislav Petkov , Masami Hiramatsu Date: Thu, 10 Dec 2015 10:46:30 +0900 Message-ID: <20151210014630.25437.94161.stgit@softrs> In-Reply-To: <20151210014624.25437.50028.stgit@softrs> References: <20151210014624.25437.50028.stgit@softrs> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5202 Lines: 164 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 atomic_t panic_cpu. V6: - Use PANIC_CPU_INVALID instead of hard-coded -1 - Add comments about __crash_kexec() V5: - Add missing dummy __crash_kexec() for !CONFIG_KEXEC_CORE case - Replace atomic_xchg() with atomic_set() in crash_kexec() because it is used as a release operation and there is no need of memory barrier effect. This change also removes an unused value warning V4: - Use new __crash_kexec(), no exclusion check version of crash_kexec(), instead of checking if panic_cpu is the current CPU or not V2: - Use atomic_cmpxchg() instead of spin_trylock() on panic_lock to exclude concurrent accesses - Don't introduce no-lock version of crash_kexec() Signed-off-by: Hidehiro Kawai Cc: Eric Biederman Cc: Vivek Goyal Cc: Andrew Morton Cc: Michal Hocko --- include/linux/kexec.h | 2 ++ kernel/kexec_core.c | 30 +++++++++++++++++++++++++++++- kernel/panic.c | 4 ++-- 3 files changed, 33 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 3d6c3f1..81a0a3d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -138,7 +138,7 @@ void panic(const char *fmt, ...) * the "crash_kexec_post_notifiers" option to the kernel. */ if (!crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); /* bypass panic_cpu check */ /* * Note smp_send_stop is the usual smp shutdown function, which @@ -163,7 +163,7 @@ void panic(const char *fmt, ...) * more unstable, it can increase risks of the kdump failure too. */ if (crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); /* bypass panic_cpu check */ 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/