From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C27CECE58E for ; Thu, 17 Oct 2019 12:34:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DF2A42067B for ; Thu, 17 Oct 2019 12:34:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406278AbfJQMeZ (ORCPT ); Thu, 17 Oct 2019 08:34:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:41362 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727291AbfJQMeZ (ORCPT ); Thu, 17 Oct 2019 08:34:25 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 911042082C; Thu, 17 Oct 2019 12:34:23 +0000 (UTC) Date: Thu, 17 Oct 2019 08:34:22 -0400 From: Steven Rostedt To: Prateek Sood Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, kaushalk@codeaurora.org, Peter Zijlstra Subject: Re: [PATCH] trace: fix race in perf_trace_buf initialization Message-ID: <20191017083422.6ab65ce2@gandalf.local.home> In-Reply-To: References: <1571120245-4186-1-git-send-email-prsood@codeaurora.org> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Oct 2019 12:23:49 +0530 Prateek Sood wrote: > On 10/15/19 11:47 AM, Prateek Sood wrote: > > [ 943.034988] Unable to handle kernel paging request at virtual address 0000003106f2003c > > [ 943.043653] Mem abort info: > > [ 943.046679] ESR = 0x96000045 > > [ 943.050428] Exception class = DABT (current EL), IL = 32 bits > > [ 943.056643] SET = 0, FnV = 0 > > [ 943.060168] EA = 0, S1PTW = 0 > > [ 943.063449] Data abort info: > > [ 943.066474] ISV = 0, ISS = 0x00000045 > > [ 943.070856] CM = 0, WnR = 1 > > [ 943.074016] user pgtable: 4k pages, 39-bit VAs, pgdp = ffffffc034b9b000 > > [ 943.081446] [0000003106f2003c] pgd=0000000000000000, pud=0000000000000000 > > [ 943.088862] Internal error: Oops: 96000045 [#1] PREEMPT SMP > > [ 943.141700] Process syz-executor (pid: 18393, stack limit = 0xffffffc093190000) > > [ 943.164146] pstate: 80400005 (Nzcv daif +PAN -UAO) > > [ 943.169119] pc : __memset+0x20/0x1ac > > [ 943.172831] lr : memset+0x3c/0x50 > > [ 943.176269] sp : ffffffc09319fc50 > > > > [ 943.557593] __memset+0x20/0x1ac > > [ 943.560953] perf_trace_buf_alloc+0x140/0x1a0 > > [ 943.565472] perf_trace_sys_enter+0x158/0x310 > > [ 943.569985] syscall_trace_enter+0x348/0x7c0 > > [ 943.574413] el0_svc_common+0x11c/0x368 > > [ 943.578394] el0_svc_handler+0x12c/0x198 > > [ 943.582459] el0_svc+0x8/0xc > > > > In Ramdumps: > > total_ref_count = 3 > > perf_trace_buf = ( > > 0x0 -> NULL, > > 0x0 -> NULL, > > 0x0 -> NULL, > > 0x0 -> NULL) > > > > event_call in perf_trace_sys_enter() > > event_call = 0xFFFFFF900CB511D8 -> ( > > list = (next = 0xFFFFFF900CB4E2E0, prev = 0xFFFFFF900CB512B0), > > class = 0xFFFFFF900CDC8308, > > name = 0xFFFFFF900CDDA1D8, > > tp = 0xFFFFFF900CDDA1D8, > > event = ( > > node = (next = 0x0, pprev = 0xFFFFFF900CB80210), > > list = (next = 0xFFFFFF900CB512E0, prev = 0xFFFFFF900CB4E310), > > type = 21, > > funcs = 0xFFFFFF900CB51130), > > print_fmt = 0xFFFFFF900CB51150, > > filter = 0x0, > > mod = 0x0, > > data = 0x0, > > flags = 18, > > perf_refcount = 1, > > perf_events = 0xFFFFFF8DB8E54158, > > prog_array = 0x0, > > perf_perm = 0x0) > > > > perf_events added on CPU0 > > (struct hlist_head *)(0xFFFFFF8DB8E54158+__per_cpu_offset[0]) -> ( > > first = 0xFFFFFFC0980FD0E0 -> ( > > next = 0x0, > > pprev = 0xFFFFFFBEBFD74158)) > > > > Could you please confirm: > > 1) the race mentioned below exists or not. > > 2) if following patch fixes it. > > > > > >> 8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8 > > > > A race condition exists while initialiazing perf_trace_buf from > > perf_trace_init() and perf_kprobe_init(). > > > > CPU0 CPU1 > > perf_trace_init() > > mutex_lock(&event_mutex) > > perf_trace_event_init() > > perf_trace_event_reg() > > total_ref_count == 0 > > buf = alloc_percpu() > > perf_trace_buf[i] = buf > > tp_event->class->reg() //fails perf_kprobe_init() > > goto fail perf_trace_event_init() > > perf_trace_event_reg() > > fail: > > total_ref_count == 0 > > > > total_ref_count == 0 > > buf = alloc_percpu() > > perf_trace_buf[i] = buf > > tp_event->class->reg() > > total_ref_count++ > > > > free_percpu(perf_trace_buf[i]) > > perf_trace_buf[i] = NULL > > > > Any subsequent call to perf_trace_event_reg() will observe total_ref_count > 0, > > causing the perf_trace_buf to be NULL always. This can result in perf_trace_buf > > getting accessed from perf_trace_buf_alloc() without being initialized. Acquiring > > event_mutex in perf_kprobe_init() before calling perf_trace_event_init() should > > fix this race. > > > > Signed-off-by: Prateek Sood > > --- > > kernel/trace/trace_event_perf.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c > > index 4629a61..48ee92c 100644 > > --- a/kernel/trace/trace_event_perf.c > > +++ b/kernel/trace/trace_event_perf.c > > @@ -272,9 +272,11 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe) > > goto out; > > } > > > > + mutex_lock(&event_mutex); > > ret = perf_trace_event_init(tp_event, p_event); > > if (ret) > > destroy_local_trace_kprobe(tp_event); > > + mutex_unlock(&event_mutex); > > out: > > kfree(func); > > return ret; > > @@ -282,8 +284,10 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe) > > > > void perf_kprobe_destroy(struct perf_event *p_event) > > { > > + mutex_lock(&event_mutex); > > perf_trace_event_close(p_event); > > perf_trace_event_unreg(p_event); > > + mutex_unlock(&event_mutex); > > > > destroy_local_trace_kprobe(p_event->tp_event); > > } > > > > Folks, > > Could you please help with this query/patch? Added Peter Zijlstra who maintains the kernel side of perf. -- Steve