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 910CDECAAD2 for ; Fri, 26 Aug 2022 08:21:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245205AbiHZIVz (ORCPT ); Fri, 26 Aug 2022 04:21:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55696 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244988AbiHZIVv (ORCPT ); Fri, 26 Aug 2022 04:21:51 -0400 Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com [94.136.29.106]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C128C120F; Fri, 26 Aug 2022 01:21:50 -0700 (PDT) Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 4A96643549; Fri, 26 Aug 2022 10:21:47 +0200 (CEST) Message-ID: <3ea2a6b3-d64d-744f-894b-66fee1242597@proxmox.com> Date: Fri, 26 Aug 2022 10:21:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 From: Fiona Ebner Subject: Re: Problematic interaction of io_uring and CIFS To: Shyam Prasad N , Enzo Matsumiya , Jens Axboe Cc: io-uring@vger.kernel.org, CIFS , Thomas Lamprecht References: <20220708174815.3g4atpcu6u6icrhp@cyberdelia> <560586b2-8cd6-7a62-86f2-90e8968d0ad4@proxmox.com> Content-Language: en-US In-Reply-To: <560586b2-8cd6-7a62-86f2-90e8968d0ad4@proxmox.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Am 11.07.22 um 15:40 schrieb Fabian Ebner: > Am 09.07.22 um 05:39 schrieb Shyam Prasad N: >> On Sat, Jul 9, 2022 at 9:00 AM Shyam Prasad N wrote: >>> >>> On Fri, Jul 8, 2022 at 11:22 PM Enzo Matsumiya wrote: >>>> >>>> On 07/08, Fabian Ebner wrote: >>>>> (Re-sending without the log from the older kernel, because the mail hit >>>>> the 100000 char limit with that) >>>>> >>>>> Hi, >>>>> it seems that in kernels >= 5.15, io_uring and CIFS don't interact >>>>> nicely sometimes, leading to IO errors. Unfortunately, my reproducer is >>>>> a QEMU VM with a disk on CIFS (original report by one of our users [0]), >>>>> but I can try to cook up something simpler if you want. >>>>> >>>>> Bisecting got me to 8ef12efe26c8 ("io_uring: run regular file >>>>> completions from task_work") being the first bad commit. >>>>> I finally got around to taking another look at this issue (still present in 5.19.3) and I think I've finally figured out the root cause: After commit 8ef12efe26c8, for my reproducer, the write completion is added to task_work with notify_method being TWA_SIGNAL and thus TIF_NOTIFY_SIGNAL is set for the task. After that, if we end up in sk_stream_wait_memory() via sock_sendmsg(), signal_pending(current) will evaluate to true and thus -EINTR is returned all the way up to sock_sendmsg() in smb_send_kvec(). Related: in __smb_send_rqst() there too is a signal_pending(current) check leading to the -ERESTARTSYS return value. To verify that this is the cause, I wasn't able to trigger the issue anymore with this hack applied (i.e. excluding the TIF_NOTIFY_SIGNAL check): > diff --git a/net/core/stream.c b/net/core/stream.c > index 06b36c730ce8..58e3825930bb 100644 > --- a/net/core/stream.c > +++ b/net/core/stream.c > @@ -134,7 +134,7 @@ int sk_stream_wait_memory(struct sock *sk, long *timeo_p) > goto do_error; > if (!*timeo_p) > goto do_eagain; > - if (signal_pending(current)) > + if (task_sigpending(current)) > goto do_interrupted; > sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk); > if (sk_stream_memory_free(sk) && !vm_wait) In __cifs_writev() we have > /* > * If at least one write was successfully sent, then discard any rc > * value from the later writes. If the other write succeeds, then > * we'll end up returning whatever was written. If it fails, then > * we'll get a new rc value from that. > */ so it can happen that collect_uncached_write_data() will (correctly) report a short write when calling ctx->iocb->ki_complete(). But QEMU's io_uring backend treats a short write as an -ENOSPC error, which also is a bug? Or does the kernel give any guarantees in that direction? Still, it doesn't seem ideal that the "interrupt" happens and in fact __smb_send_rqst() tries to avoid it, but fails to do so, because of the unexpected TIF_NOTIFY_SIGNAL: > /* > * We should not allow signals to interrupt the network send because > * any partial send will cause session reconnects thus increasing > * latency of system calls and overload a server with unnecessary > * requests. > */ > > sigfillset(&mask); > sigprocmask(SIG_BLOCK, &mask, &oldmask); Do you have any suggestions for how to proceed? Best Regards, Fiona