From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail9.hitachi.co.jp ([133.145.228.44]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZJuQW-0003va-Ft for kexec@lists.infradead.org; Tue, 28 Jul 2015 02:15:34 +0000 Message-ID: <55B6E5AB.4070301@hitachi.com> Date: Tue, 28 Jul 2015 11:15:07 +0900 From: Hidehiro Kawai MIME-Version: 1.0 Subject: Re: [V2 PATCH 2/3] kexec: Fix race between panic() and crash_kexec() called directly References: <20150727015850.4928.87717.stgit@softrs> <20150727015850.4928.15194.stgit@softrs> <20150727145506.GG11317@dhcp22.suse.cz> In-Reply-To: <20150727145506.GG11317@dhcp22.suse.cz> 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: Michal Hocko Cc: x86@kernel.org, Jonathan Corbet , Peter Zijlstra , linux-doc@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Thomas Gleixner , "Eric W. Biederman" , "H. Peter Anvin" , Masami Hiramatsu , Andrew Morton , Ingo Molnar , Vivek Goyal Hi, (2015/07/27 23:55), Michal Hocko wrote: > On Mon 27-07-15 10:58:50, Hidehiro Kawai wrote: > [...] >> @@ -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); > > This do the opposite what the comment says, wouldn't it? You should > check old_cpu == -1. Sorry, you are right. I performed same tests as for the previous patch set, but I missed the test case for this new logic. > Also atomic_set doesn't imply memory barriers which > might be a problem. OK, I'll use atomic_xchg(). Regards, -- Hidehiro Kawai Hitachi, Ltd. Research & Development Group _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec