Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753737AbbG0FLx (ORCPT ); Mon, 27 Jul 2015 01:11:53 -0400 Received: from mail4.hitachi.co.jp ([133.145.228.5]:39000 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbbG0FLO (ORCPT ); Mon, 27 Jul 2015 01:11:14 -0400 X-AuditID: 85900ec0-9ebcbb9000001a57-76-55b5bd371ff7 X-Mailbox-Line: From nobody Mon Jul 27 10:58:50 2015 Subject: [V2 PATCH 2/3] 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: linux-doc@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Michal Hocko , Masami Hiramatsu Date: Mon, 27 Jul 2015 10:58:50 +0900 Message-ID: <20150727015850.4928.15194.stgit@softrs> In-Reply-To: <20150727015850.4928.87717.stgit@softrs> References: <20150727015850.4928.87717.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: 2674 Lines: 95 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 panicking_cpu. 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 --- kernel/kexec.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/kernel/kexec.c b/kernel/kexec.c index a785c10..ca40a19 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -1472,6 +1472,18 @@ void __weak crash_unmap_reserved_pages(void) void crash_kexec(struct pt_regs *regs) { + int old_cpu, this_cpu; + + /* + * `old_cpu == -1' means we are the first comer and crash_kexec() + * was called without entering panic(). + * `old_cpu == this_cpu' means crash_kexec() was called from panic(). + */ + this_cpu = raw_smp_processor_id(); + old_cpu = atomic_cmpxchg(&panicking_cpu, -1, this_cpu); + if (old_cpu != -1 && old_cpu != this_cpu) + return; + /* Take the kexec_mutex here to prevent sys_kexec_load * running on one cpu from replacing the crash kernel * we are using after a panic on a different cpu. @@ -1491,6 +1503,14 @@ void crash_kexec(struct pt_regs *regs) } mutex_unlock(&kexec_mutex); } + + /* + * If we came here from panic(), we have to keep panicking_cpu + * to prevent other cpus from entering panic(). Otherwise, + * resetting it so that other cpus can enter panic()/crash_kexec(). + */ + if (old_cpu == this_cpu) + atomic_set(&panicking_cpu, -1); } size_t crash_get_memory_size(void) -- 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/