From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail7.hitachi.co.jp ([133.145.228.42]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZNE1y-0001DA-Jv for kexec@lists.infradead.org; Thu, 06 Aug 2015 05:47:58 +0000 Subject: [V3 PATCH 1/4] panic/x86: Fix re-entrance problem due to panic on NMI From: Hidehiro Kawai Date: Thu, 06 Aug 2015 14:45:43 +0900 Message-ID: <20150806054543.25766.84120.stgit@softrs> In-Reply-To: <20150806054543.25766.29590.stgit@softrs> References: <20150806054543.25766.29590.stgit@softrs> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal Cc: linux-doc@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Michal Hocko , Ingo Molnar , Masami Hiramatsu 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(). 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 | 15 +++++++++++---- include/linux/kernel.h | 13 +++++++++++++ kernel/panic.c | 13 ++++++++++--- kernel/watchdog.c | 2 +- 4 files changed, 35 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index d05bd2e..dcd4038 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -231,7 +231,7 @@ void unregister_nmi_handler(unsigned int type, const char *name) #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 +255,15 @@ void unregister_nmi_handler(unsigned int type, const char *name) 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 here, we've already being in 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 +304,7 @@ void unregister_nmi_handler(unsigned int type, const char *name) 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 5582410..57c33da 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -443,6 +443,19 @@ extern __scanf(2, 0) extern bool crash_kexec_post_notifiers; +extern atomic_t panic_cpu; + +/* + * 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, -1, 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 04e91ff..3d4bc73 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -60,6 +60,8 @@ void __weak panic_smp_self_stop(void) cpu_relax(); } +atomic_t panic_cpu = ATOMIC_INIT(-1); + /** * panic - halt the system * @fmt: The text string to print @@ -70,17 +72,17 @@ 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(); @@ -93,8 +95,13 @@ 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 == -1' means we are the first comer. + * `old_cpu == this_cpu' means we came here due to panic on NMI. */ - if (!spin_trylock(&panic_lock)) + this_cpu = raw_smp_processor_id(); + old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu); + if (old_cpu != -1 && old_cpu != this_cpu) panic_smp_self_stop(); console_verbose(); diff --git a/kernel/watchdog.c b/kernel/watchdog.c index a6ffa43..9a3d738 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -304,7 +304,7 @@ static void watchdog_overflow_callback(struct perf_event *event, return; if (hardlockup_panic) - panic("Watchdog detected hard LOCKUP on cpu %d", + nmi_panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu); else WARN(1, "Watchdog detected hard LOCKUP on cpu %d", _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec