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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 D6E3BC433E0 for ; Mon, 18 May 2020 18:02:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B60AC21534 for ; Mon, 18 May 2020 18:02:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824954; bh=MnVZ8YB95EmxBqxmwt11FwSNiLoPIlEMw9ZmUH95iPU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Q+TBbr34+sfg8qGSn4tbOUHSRc0FPLRI/UxfiAcMqNH9I0e6ilvgPKJVXrLD4+COb 6UKs4QvojiwKsjkpsm9fPLuw5BiqGElHGMARHzBXBmPIUN5NMyd1UeH7S5G4Xh74aP iUhSPaAYPf4dH33q+IQ+09PzGk/7glV3Z3a09z3s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732545AbgERSCe (ORCPT ); Mon, 18 May 2020 14:02:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:46618 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732531AbgERSCa (ORCPT ); Mon, 18 May 2020 14:02:30 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 D6FD020826; Mon, 18 May 2020 18:02:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824949; bh=MnVZ8YB95EmxBqxmwt11FwSNiLoPIlEMw9ZmUH95iPU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RxutOka6SeVHp3vguSYoZ7+oH6OPfb6wDI8GUBal7E9DV8zXfMSdEDhWlh8q7jftn KEslEUhlMhB0o2jNIXz/Uvvyu0Q290i5qtawD1bsJuMZ2WLfffcazZYhUpSMMVvyEA wwkdT89V9X1rsSJj02BrC9rb1EzOu32dnprUHTGU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Xiaoguang Wang , Jens Axboe , Sasha Levin Subject: [PATCH 5.6 067/194] io_uring: use cond_resched() in io_ring_ctx_wait_and_kill() Date: Mon, 18 May 2020 19:35:57 +0200 Message-Id: <20200518173537.317015147@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173531.455604187@linuxfoundation.org> References: <20200518173531.455604187@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xiaoguang Wang [ Upstream commit 3fd44c86711f71156b586c22b0495c58f69358bb ] While working on to make io_uring sqpoll mode support syscalls that need struct files_struct, I got cpu soft lockup in io_ring_ctx_wait_and_kill(), while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait)) cpu_relax(); above loop never has an chance to exit, it's because preempt isn't enabled in the kernel, and the context calling io_ring_ctx_wait_and_kill() and io_sq_thread() run in the same cpu, if io_sq_thread calls a cond_resched() yield cpu and another context enters above loop, then io_sq_thread() will always in runqueue and never exit. Use cond_resched() can fix this issue. Reported-by: syzbot+66243bb7126c410cefe6@syzkaller.appspotmail.com Signed-off-by: Xiaoguang Wang Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- fs/io_uring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 9690c845a3e4b..01f71b9efb88f 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6451,7 +6451,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx) * it could cause shutdown to hang. */ while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait)) - cpu_relax(); + cond_resched(); io_kill_timeouts(ctx); io_poll_remove_all(ctx); -- 2.20.1