Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754241AbbLJBu5 (ORCPT ); Wed, 9 Dec 2015 20:50:57 -0500 Received: from mail9.hitachi.co.jp ([133.145.228.44]:41523 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751416AbbLJBtU (ORCPT ); Wed, 9 Dec 2015 20:49:20 -0500 X-AuditID: 85900ec0-9afc5b9000001a57-d1-5668da1ba8c6 X-Mailbox-Line: From nobody Thu Dec 10 10:46:28 2015 Subject: [V6 PATCH 1/6] panic/x86: Fix re-entrance problem due to panic on NMI 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 , Ingo Molnar , Borislav Petkov , Masami Hiramatsu Date: Thu, 10 Dec 2015 10:46:26 +0900 Message-ID: <20151210014626.25437.13302.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: 5887 Lines: 181 If panic on NMI happens just after panic() on the same CPU, panic() is recursively called. As the result, it stalls after failing to acquire panic_lock. To avoid this problem, don't call panic() in NMI context if we've already entered panic(). V6: - Add a comment about panic_cpu - Replace the magic number -1 for panic_cpu with a macro V4: - Improve comments in io_check_error() and panic() V3: - Introduce nmi_panic() macro to reduce code duplication - In the case of panic on NMI, don't return from NMI handlers if another CPU already panicked V2: - Use atomic_cmpxchg() instead of current spin_trylock() to exclude concurrent accesses to the panic routines - Don't introduce no-lock version of panic() Signed-off-by: Hidehiro Kawai Cc: Andrew Morton Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: Michal Hocko --- arch/x86/kernel/nmi.c | 16 ++++++++++++---- include/linux/kernel.h | 21 +++++++++++++++++++++ kernel/panic.c | 15 ++++++++++++--- kernel/watchdog.c | 2 +- 4 files changed, 46 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 697f90d..5131714 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -231,7 +231,7 @@ pci_serr_error(unsigned char reason, struct pt_regs *regs) #endif if (panic_on_unrecovered_nmi) - panic("NMI: Not continuing"); + nmi_panic("NMI: Not continuing"); pr_emerg("Dazed and confused, but trying to continue\n"); @@ -255,8 +255,16 @@ io_check_error(unsigned char reason, struct pt_regs *regs) reason, smp_processor_id()); show_regs(regs); - if (panic_on_io_nmi) - panic("NMI IOCK error: Not continuing"); + if (panic_on_io_nmi) { + nmi_panic("NMI IOCK error: Not continuing"); + + /* + * If we return from nmi_panic(), it means we have received + * NMI while processing panic(). So, simply return without + * a delay and re-enabling NMI. + */ + return; + } /* Re-enable the IOCK line, wait for a few seconds */ reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK; @@ -297,7 +305,7 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs) pr_emerg("Do you have a strange power saving mode enabled?\n"); if (unknown_nmi_panic || panic_on_unrecovered_nmi) - panic("NMI: Not continuing"); + nmi_panic("NMI: Not continuing"); pr_emerg("Dazed and confused, but trying to continue\n"); } diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 350dfb0..db66867 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -446,6 +446,27 @@ extern int sysctl_panic_on_stackoverflow; extern bool crash_kexec_post_notifiers; /* + * panic_cpu holds a panicking CPU number and is used for exclusive + * execution of panic and crash_kexec routines. If the value is + * PANIC_CPU_INVALID, it means that none of CPU has entered panic or + * crash_kexec. + */ +extern atomic_t panic_cpu; +#define PANIC_CPU_INVALID -1 + +/* + * A variant of panic() called from NMI context. + * If we've already panicked on this CPU, return from here. + */ +#define nmi_panic(fmt, ...) \ + do { \ + int this_cpu = raw_smp_processor_id(); \ + if (atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu) \ + != this_cpu) \ + panic(fmt, ##__VA_ARGS__); \ + } while (0) + +/* * Only to be used by arch init code. If the user over-wrote the default * CONFIG_PANIC_TIMEOUT, honor it. */ diff --git a/kernel/panic.c b/kernel/panic.c index 4b150bc..3261e2d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -61,6 +61,8 @@ void __weak panic_smp_self_stop(void) cpu_relax(); } +atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID); + /** * panic - halt the system * @fmt: The text string to print @@ -71,17 +73,17 @@ void __weak panic_smp_self_stop(void) */ void panic(const char *fmt, ...) { - static DEFINE_SPINLOCK(panic_lock); static char buf[1024]; va_list args; long i, i_next = 0; int state = 0; + int old_cpu, this_cpu; /* * Disable local interrupts. This will prevent panic_smp_self_stop * from deadlocking the first cpu that invokes the panic, since * there is nothing to prevent an interrupt handler (that runs - * after the panic_lock is acquired) from invoking panic again. + * after setting panic_cpu) from invoking panic again. */ local_irq_disable(); @@ -94,8 +96,15 @@ void panic(const char *fmt, ...) * multiple parallel invocations of panic, all other CPUs either * stop themself or will wait until they are stopped by the 1st CPU * with smp_send_stop(). + * + * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which + * comes here, so go ahead. + * `old_cpu == this_cpu' means we came from nmi_panic() which sets + * panic_cpu to this CPU. In this case, this is also the 1st CPU. */ - if (!spin_trylock(&panic_lock)) + this_cpu = raw_smp_processor_id(); + old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); + if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu) panic_smp_self_stop(); console_verbose(); diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 18f34cf..b9be18f 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -351,7 +351,7 @@ static void watchdog_overflow_callback(struct perf_event *event, trigger_allbutself_cpu_backtrace(); if (hardlockup_panic) - panic("Hard LOCKUP"); + nmi_panic("Hard LOCKUP"); __this_cpu_write(hard_watchdog_warn, true); return; -- 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/