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 90E67C2BB1D for ; Tue, 14 Apr 2020 22:29:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 437AE20656 for ; Tue, 14 Apr 2020 22:29:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="TgO5s5Ul" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391986AbgDNW3h (ORCPT ); Tue, 14 Apr 2020 18:29:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S2391879AbgDNW3d (ORCPT ); Tue, 14 Apr 2020 18:29:33 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1217FC061A0C for ; Tue, 14 Apr 2020 15:29:33 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id w15so13455571ybp.16 for ; Tue, 14 Apr 2020 15:29:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=l6V3U7dW8FQhAMlxw/7mM2Vqfwhiq7K4HBOf1qSKOAc=; b=TgO5s5UlJ4/uM4wFtCJu+NZhbygclu6fzmMpGxb7r8iB+bVsyfF93x3MCJiJng41a2 XW2DQAM6muv6LoYuZLZR2THptu7UyXK91c5F3EaSrki8rAjxngCuauqEOKSdS5z/GiBg r/W6Tz5i3bF3YMbR4AkNHbxkkbe4kUWuwNQtP6uO+HUKqV3VSo8ZasgbqmFraTHmp16L gpyRpWOppi+m45gu6ic/M6kS2dP2MBZTI7ofRhbXtoyHNUUL2N3ypX1wL1wlMGNaD/mb pElTUS3oFTuv95xIzzPEhI2zGh0WGnUK3jnFi6ibsG5TJgndNVM01/q2oH0g5lZniq80 VgcA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=l6V3U7dW8FQhAMlxw/7mM2Vqfwhiq7K4HBOf1qSKOAc=; b=Lq32oBhKR1efIftxRVxacg0JZLTFpJawuWwAQrfjUVODHRCfSAm2RYVk8uLWMnbvGb NLv6Y9KEoxFa8U45YlVpBzthSF47nXwFxMD1H6pUREM8+qaLXlHvP65RcgrhRbd+U7h4 9hTei/XlmKJTUTYPIodf0xErFnUAqUSchI3NhhcdYqhRpCtx1w3WhDHc5p+EPUkEXy5d wn+2ugJOHcOlmtcwsX8c6IIC0sL+5WlSyg9g5mdVWzTJT6WT1kOYdjcODeugjB0ke40C 76y+IML+uAWaMTAZ5w5Qy39orT97PrKJ3KYSyXAIX5iPVW0nbshF07MywtmJCFmp2nWh OeYQ== X-Gm-Message-State: AGi0PubgUmJ2OL+fYlL7xbr6fRH/tc0eZ3srFJR9veG5Hpup4yvg4Jqf 7OA/S5hMznEP9xit3oYNJkTQmDuq X-Google-Smtp-Source: APiQypL5Aab2OXLR0AADmfFVydjCRo8x7V9fXaPyOfYZpMTdgU3TdbJPRm0yywzOHB/u0WgTotFsa0vh X-Received: by 2002:a25:d382:: with SMTP id e124mr3666231ybf.162.1586903371782; Tue, 14 Apr 2020 15:29:31 -0700 (PDT) Date: Tue, 14 Apr 2020 18:29:20 -0400 In-Reply-To: <20200414190351.16893-1-brho@google.com> Message-Id: <20200414222920.121401-1-brho@google.com> Mime-Version: 1.0 References: <20200414190351.16893-1-brho@google.com> 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 | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 55e44417f66d..bcafd7b992b3 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -95,11 +95,11 @@ static void remote_function(void *data) * @info: the function call argument * * Calls the function @func when the task is currently running. This might - * be on the current CPU, which just calls the function directly + * be on the current CPU, which just calls the function directly. This will + * retry due to any failures in smp_call_function_single(), such as if the + * task_cpu() goes offline concurrently. * - * returns: @func return value, or - * -ESRCH - when the process isn't running - * -EAGAIN - when the process moved away + * returns @func return value or -ESRCH when the process isn't running */ static int task_function_call(struct task_struct *p, remote_function_f func, void *info) @@ -112,11 +112,16 @@ 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); - if (!ret) - ret = data.ret; - } while (ret == -EAGAIN); + for (;;) { + ret = smp_call_function_single(task_cpu(p), remote_function, + &data, 1); + ret = !ret ? data.ret : -EAGAIN; + + if (ret != -EAGAIN) + break; + + cond_resched(); + } return ret; } -- 2.26.0.110.g2183baf09c-goog