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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCC61EB64DD for ; Sun, 16 Jul 2023 20:56:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233052AbjGPU4V (ORCPT ); Sun, 16 Jul 2023 16:56:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233053AbjGPU4U (ORCPT ); Sun, 16 Jul 2023 16:56:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A799E41 for ; Sun, 16 Jul 2023 13:56:18 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C32D760EAE for ; Sun, 16 Jul 2023 20:56:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7C7CC433C8; Sun, 16 Jul 2023 20:56:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1689540977; bh=TWu0evTuPxw936WiDTsRfIjShbqTRbY34OcOiEIALVE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wNol2IlHsxOExcSCE6tJirKi4a6x25P5Nknjk1KLBXMpFuiAsHapwXHz8N/0EDsmX aPWhKNPr/djNXJs8b+RdmEAl79LJ52Crd89A1J8eDxZf+Ua46nRmDKFzBIgX9uSrOa KKz8uS+EF3Xs95c1xIGWkw4jz8dP7yqYg2da14wM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jens Axboe Subject: [PATCH 6.1 528/591] io_uring: wait interruptibly for request completions on exit Date: Sun, 16 Jul 2023 21:51:07 +0200 Message-ID: <20230716194937.532775800@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230716194923.861634455@linuxfoundation.org> References: <20230716194923.861634455@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Jens Axboe commit 4826c59453b3b4677d6bf72814e7ababdea86949 upstream. WHen the ring exits, cleanup is done and the final cancelation and waiting on completions is done by io_ring_exit_work. That function is invoked by kworker, which doesn't take any signals. Because of that, it doesn't really matter if we wait for completions in TASK_INTERRUPTIBLE or TASK_UNINTERRUPTIBLE state. However, it does matter to the hung task detection checker! Normally we expect cancelations and completions to happen rather quickly. Some test cases, however, will exit the ring and park the owning task stopped (eg via SIGSTOP). If the owning task needs to run task_work to complete requests, then io_ring_exit_work won't make any progress until the task is runnable again. Hence io_ring_exit_work can trigger the hung task detection, which is particularly problematic if panic-on-hung-task is enabled. As the ring exit doesn't take signals to begin with, have it wait interruptibly rather than uninterruptibly. io_uring has a separate stuck-exit warning that triggers independently anyway, so we're not really missing anything by making this switch. Cc: stable@vger.kernel.org # 5.10+ Link: https://lore.kernel.org/r/b0e4aaef-7088-56ce-244c-976edeac0e66@kernel.dk Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- io_uring/io_uring.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2748,7 +2748,18 @@ static __cold void io_ring_exit_work(str /* there is little hope left, don't run it too often */ interval = HZ * 60; } - } while (!wait_for_completion_timeout(&ctx->ref_comp, interval)); + /* + * This is really an uninterruptible wait, as it has to be + * complete. But it's also run from a kworker, which doesn't + * take signals, so it's fine to make it interruptible. This + * avoids scenarios where we knowingly can wait much longer + * on completions, for example if someone does a SIGSTOP on + * a task that needs to finish task_work to make this loop + * complete. That's a synthetic situation that should not + * cause a stuck task backtrace, and hence a potential panic + * on stuck tasks if that is enabled. + */ + } while (!wait_for_completion_interruptible_timeout(&ctx->ref_comp, interval)); init_completion(&exit.completion); init_task_work(&exit.task_work, io_tctx_exit_cb); @@ -2772,7 +2783,12 @@ static __cold void io_ring_exit_work(str continue; mutex_unlock(&ctx->uring_lock); - wait_for_completion(&exit.completion); + /* + * See comment above for + * wait_for_completion_interruptible_timeout() on why this + * wait is marked as interruptible. + */ + wait_for_completion_interruptible(&exit.completion); mutex_lock(&ctx->uring_lock); } mutex_unlock(&ctx->uring_lock);