From patchwork Fri Sep 22 16:34:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mikulas Patocka X-Patchwork-Id: 13396015 X-Patchwork-Delegate: herbert@gondor.apana.org.au 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 D5DCFCD4846 for ; Fri, 22 Sep 2023 16:35:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229789AbjIVQfM (ORCPT ); Fri, 22 Sep 2023 12:35:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229621AbjIVQfL (ORCPT ); Fri, 22 Sep 2023 12:35:11 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A2D4114 for ; Fri, 22 Sep 2023 09:34:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695400461; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vliUwCegH4eIRf5XC0HvBAS7inlKlSLddwzJmmiHBAg=; b=hy7t+mnV+4o7S2cwWWO0SOuUPjuvcxCAlkpnNDPCEm7+Q4U8MaBkc+hz9jafkPBHM+0cVb ltH5JFCYP9YVGSbcLa3MsolNKiWViUcLrHgSdJptSwvJguH4r//6/TVJdxvuhwfTo1sNa9 O9r7lKs2Vj4PfQWIZ77pxvqX23ppyRc= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-601-CdRADtmcNDOxspbYMYAbBg-1; Fri, 22 Sep 2023 12:34:18 -0400 X-MC-Unique: CdRADtmcNDOxspbYMYAbBg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 53A851C05B13; Fri, 22 Sep 2023 16:34:17 +0000 (UTC) Received: from file1-rdu.file-001.prod.rdu2.dc.redhat.com (unknown [10.11.5.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E784720268D6; Fri, 22 Sep 2023 16:34:16 +0000 (UTC) Received: by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix, from userid 12668) id CF52130C1C0A; Fri, 22 Sep 2023 16:34:16 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix) with ESMTP id CA2403FB77; Fri, 22 Sep 2023 18:34:16 +0200 (CEST) Date: Fri, 22 Sep 2023 18:34:16 +0200 (CEST) From: Mikulas Patocka To: Giovanni Cabiddu cc: Herbert Xu , "David S. Miller" , Michael Hrivnak , Eric Garver , qat-linux@intel.com, linux-crypto@vger.kernel.org, dm-devel@redhat.com Subject: [PATCH v2] qat: fix deadlock in backlog processing In-Reply-To: Message-ID: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Hi On Fri, 22 Sep 2023, Giovanni Cabiddu wrote: > Hi Mikulas, > > many thanks for reporting this issue and finding a solution. > > On Thu, Sep 21, 2023 at 10:53:55PM +0200, Mikulas Patocka wrote: > > I was evaluating whether it is feasible to use QAT with dm-crypt (the > > answer is that it is not - QAT is slower than AES-NI for this type of > > workload; QAT starts to be benefical for encryption requests longer than > > 64k). > Correct. Is there anything that we can do to batch requests in a single > call? Ask Herbert Xu. I think it would complicate the design of crypto API. > Sometime ago there was some work done to build a geniv template cipher > and optimize dm-crypt to encrypt larger block sizes in a single call, > see [1][2]. Don't know if that work was completed. > > >And I got some deadlocks. > Ouch! > > > The reason for the deadlocks is this: suppose that one of the "if" > > conditions in "qat_alg_send_message_maybacklog" is true and we jump to the > > "enqueue" label. At this point, an interrupt comes in and clears all > > pending messages. Now, the interrupt returns, we grab backlog->lock, add > > the message to the backlog, drop backlog->lock - and there is no one to > > remove the backlogged message out of the list and submit it. > Makes sense. In my testing I wasn't able to reproduce this condition. I reproduced it with this: Use a system with two Intel(R) Xeon(R) Gold 5420+ processors Use a kernel 6.6-rc2 Patch the kernel, so that dm-crypt uses QAT - that is, in drivers/md/dm-crypt.c, replace all strings "CRYPTO_ALG_ALLOCATES_MEMORY" with "0" Use .config from RHEL-9.4 beta and compile the kernel On the system, disable hyperthreading with "echo off >/sys/devices/system/cpu/smt/control" Activate dm-crypt on the top of nvme: "cryptsetup create cr /dev/nvme3n1 --sector-size=4096" Run fio in a loop: "while true; do fio --ioengine=psync --iodepth=1 --rw=randwrite --direct=1 --end_fsync=1 --bs=64k --numjobs=56 --time_based --runtime=10 --group_reporting --name=job --filename=/dev/mapper/cr done" With this setup, I get a deadlock in a few iterations of fio. > > I fixed it with this patch - with this patch, the test passes and there > > are no longer any deadlocks. I didn't want to add a spinlock to the hot > > path, so I take it only if some of the condition suggests that queuing may > > be required. > > > > Signed-off-by: Mikulas Patocka > > Cc: stable@vger.kernel.org > The commit message requires a bit of rework to describe the change. I improved the message and I send a second version of the patch. > Also, deserves a fixes tag. "Fixes" tag is for something that worked and that was broken in some previous commit. A quick search through git shows that QAT backlogging was broken since the introduction of QAT. > > > > --- > > drivers/crypto/intel/qat/qat_common/qat_algs_send.c | 31 ++++++++++++-------- > > 1 file changed, 20 insertions(+), 11 deletions(-) > > > > Index: linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c > > =================================================================== > > --- linux-2.6.orig/drivers/crypto/intel/qat/qat_common/qat_algs_send.c > > +++ linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c > > @@ -40,16 +40,6 @@ void qat_alg_send_backlog(struct qat_ins > > spin_unlock_bh(&backlog->lock); > > } > > > > -static void qat_alg_backlog_req(struct qat_alg_req *req, > > - struct qat_instance_backlog *backlog) > > -{ > > - INIT_LIST_HEAD(&req->list); > Is the initialization of an element no longer needed? It was never needed. list_add_tail calls __list_add and __list_add overwrites new->next and new->prev without reading them. So, there's no need to initialize them. > > - > > - spin_lock_bh(&backlog->lock); > > - list_add_tail(&req->list, &backlog->list); > > - spin_unlock_bh(&backlog->lock); > > -} > > - > > static int qat_alg_send_message_maybacklog(struct qat_alg_req *req) > > { > > struct qat_instance_backlog *backlog = req->backlog; > > @@ -71,8 +61,27 @@ static int qat_alg_send_message_maybackl > > return -EINPROGRESS; > > > > enqueue: > > - qat_alg_backlog_req(req, backlog); > > + spin_lock_bh(&backlog->lock); > > + > > + /* If any request is already backlogged, then add to backlog list */ > > + if (!list_empty(&backlog->list)) > > + goto enqueue2; > > > > + /* If ring is nearly full, then add to backlog list */ > > + if (adf_ring_nearly_full(tx_ring)) > > + goto enqueue2; > > + > > + /* If adding request to HW ring fails, then add to backlog list */ > > + if (adf_send_message(tx_ring, fw_req)) > > + goto enqueue2; > In a nutshell, you are re-doing the same steps taking the backlog lock. > > It should be possible to re-write it so that there is a function that > attempts enqueuing and if it fails, then the same is called again taking > the lock. > If you want I can rework it and resubmit. Yes, if you prefer it this way, I reworked the patch so that we execute the same code with or without the spinlock held. > > + > > + spin_unlock_bh(&backlog->lock); > > + return -EINPROGRESS; > > + > > +enqueue2: > > + list_add_tail(&req->list, &backlog->list); > > + > > + spin_unlock_bh(&backlog->lock); > > return -EBUSY; > > } > > [1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1276510.html > [2] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1428293.html > > Regards, > > -- > Giovanni > From: Mikulas Patocka Subject: [PATCH] qat: fix deadlock in backlog processing I was testing QAT with dm-crypt and I got some deadlocks. The reason for the deadlocks is this: suppose that one of the "if" conditions in "qat_alg_send_message_maybacklog" is true and we jump to the "enqueue" label. At this point, an interrupt comes in and clears all pending messages. Now, the interrupt returns, we grab backlog->lock, add the message to the backlog, drop backlog->lock - and there is no one to remove the backlogged message out of the list and submit it. In order to fix the bug, we must hold the spinlock backlog->lock when we perform test for free space in the ring - so that the test for free space and adding the request to a backlog is atomic and can't be interrupted by an interrupt. Every completion interrupt calls qat_alg_send_backlog which grabs backlog->lock, so holding this spinlock is sufficient to synchronize with interrupts. I didn't want to add a spinlock unconditionally to the hot path for performance reasons, so I take it only if some of the condition suggests that queuing may be required. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org --- drivers/crypto/intel/qat/qat_common/qat_algs_send.c | 23 ++++++++++---------- 1 file changed, 12 insertions(+), 11 deletions(-) Index: linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c =================================================================== --- linux-2.6.orig/drivers/crypto/intel/qat/qat_common/qat_algs_send.c +++ linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c @@ -40,22 +40,14 @@ void qat_alg_send_backlog(struct qat_ins spin_unlock_bh(&backlog->lock); } -static void qat_alg_backlog_req(struct qat_alg_req *req, - struct qat_instance_backlog *backlog) -{ - INIT_LIST_HEAD(&req->list); - - spin_lock_bh(&backlog->lock); - list_add_tail(&req->list, &backlog->list); - spin_unlock_bh(&backlog->lock); -} - static int qat_alg_send_message_maybacklog(struct qat_alg_req *req) { struct qat_instance_backlog *backlog = req->backlog; struct adf_etr_ring_data *tx_ring = req->tx_ring; u32 *fw_req = req->fw_req; + bool locked = false; +repeat: /* If any request is already backlogged, then add to backlog list */ if (!list_empty(&backlog->list)) goto enqueue; @@ -68,11 +60,20 @@ static int qat_alg_send_message_maybackl if (adf_send_message(tx_ring, fw_req)) goto enqueue; + if (unlikely(locked)) + spin_unlock_bh(&backlog->lock); return -EINPROGRESS; enqueue: - qat_alg_backlog_req(req, backlog); + if (!locked) { + spin_lock_bh(&backlog->lock); + locked = true; + goto repeat; + } + + list_add_tail(&req->list, &backlog->list); + spin_unlock_bh(&backlog->lock); return -EBUSY; }