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=-17.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 1C1ACC2BB1D for ; Tue, 14 Apr 2020 19:41:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E85BC206E9 for ; Tue, 14 Apr 2020 19:41:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="re2AKKov" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2505070AbgDNTk7 (ORCPT ); Tue, 14 Apr 2020 15:40:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S2504935AbgDNTjv (ORCPT ); Tue, 14 Apr 2020 15:39:51 -0400 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B334C061A0F for ; Tue, 14 Apr 2020 12:04:17 -0700 (PDT) Received: by mail-qv1-xf49.google.com with SMTP id cf1so772022qvb.0 for ; Tue, 14 Apr 2020 12:04:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=wEXhi2KDTL49/7/ZUX9XUdxIt6VXHRWvzpEoOczneLE=; b=re2AKKovrbQOdYfoefUhsXCD8Vblkx7RtBDuhCUz9JbcE2R29tLdtqLfNNYj1W+4p+ NqmzPC7nMS9/AG0Fqf0ddPTW9pKqGgase2913Dn4nE95p/dlWLzjRnX+yKEfR6CkfTDs oHFN3/5LLwVr27dS7A3/30R/sD814WL7brDf1/QzrONVahRxKQnkk8VOCeEvu5h1pZfd RBeUDWSaWOK4RZrUONVvfEZNT6gRaZmlChQr0MvIYrvUX1loaKu9DJhtnwDoQGGu5W2X DLyzqpFKYxSVL65gzvAkCInfgxIBzeNNI+ybDDSd40m30oqTdlTDWlBhlSJF9gFYSX+9 yZvA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=wEXhi2KDTL49/7/ZUX9XUdxIt6VXHRWvzpEoOczneLE=; b=QKk8t6WN9TT3iW8g/oxPqC/Z43lrQD+KVYndv9UuKFL65CMKdB0nq+4J2LHdjSaO5m +JTu2+FtkyWrZlWHBmgnhYHvUAV/p3sJn2h7vuD9uBJwrnQZO4TGppcbXx3Txoy4KA6p dX1F/ODsekLETuXmRjT3BNRuzfeyEcreEMnycUIw44HR4dOrOCk1qbptrEBMrPXZ1BIs lpA2QCgB9PIBFxVugFh+UNA2cXeTxcrbMcysV3e0ePOa2i4wuYhnVjh4xrZh34boLs6g JcY2GuEySUo9LywlGAsE7ppPTzopLjRyjPEyYBT+p2t6B4i8xpiMvbIpLPybPhtgyqTa uyGA== X-Gm-Message-State: AGi0PuboxaE2iuU1K+myeBgrzWbQ5DE93WB2faZ82ZvHQhqd8MrPpgd6 2Ow/HwpqdJJ9rk5heBbfSgB6X8O1 X-Google-Smtp-Source: APiQypIXDaXG+77AFk7cpEZJzSlcSgxXpeGbEIvqAkcaRkEBxOkMTVXGD0JE11O6mFyQ07uoH+Ued9Ts X-Received: by 2002:ac8:31ac:: with SMTP id h41mr17598668qte.139.1586891056302; Tue, 14 Apr 2020 12:04:16 -0700 (PDT) Date: Tue, 14 Apr 2020 15:03:51 -0400 Message-Id: <20200414190351.16893-1-brho@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.26.0.110.g2183baf09c-goog Subject: perf: add cond_resched() to task_function_call() From: Barret Rhoden To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo Cc: Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-kernel@vger.kernel.org, syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Under rare circumstances, task_function_call() can repeatedly fail and cause a soft lockup. There is a slight race where the process is no longer running on the cpu we targeted by the time remote_function() runs. The code will simply try again. If we are very unlucky, this will continue to fail, until a watchdog fires. This can happen in a heavily loaded, multi-core virtual machine. Reported-by: syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.com Signed-off-by: Barret Rhoden --- kernel/events/core.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 55e44417f66d..65c2c05e24c2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -99,7 +99,7 @@ static void remote_function(void *data) * * returns: @func return value, or * -ESRCH - when the process isn't running - * -EAGAIN - when the process moved away + * -ENXIO - when the cpu the process was on has gone offline */ static int task_function_call(struct task_struct *p, remote_function_f func, void *info) @@ -112,11 +112,15 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info) }; int ret; - do { - ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1); + while (1) { + ret = smp_call_function_single(task_cpu(p), remote_function, + &data, 1); if (!ret) ret = data.ret; - } while (ret == -EAGAIN); + if (ret != -EAGAIN) + break; + cond_resched(); + } return ret; } -- 2.26.0.110.g2183baf09c-goog