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 AA5BBC433EF for ; Wed, 15 Dec 2021 08:45:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240916AbhLOIpy (ORCPT ); Wed, 15 Dec 2021 03:45:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55756 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240901AbhLOIpy (ORCPT ); Wed, 15 Dec 2021 03:45:54 -0500 Received: from mail-qt1-x833.google.com (mail-qt1-x833.google.com [IPv6:2607:f8b0:4864:20::833]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5036AC06173E for ; Wed, 15 Dec 2021 00:45:54 -0800 (PST) Received: by mail-qt1-x833.google.com with SMTP id j17so21100479qtx.2 for ; Wed, 15 Dec 2021 00:45:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=from:references:in-reply-to:mime-version:thread-index:date :message-id:subject:to:cc; bh=vp2VgWPwyteTcpK4z8LYtSq1k4hJe3CpyNPgePV5ru0=; b=M63VmPPZ3ikyjqjLvSN439i8RfclCGWgSXMJZwm25R5yVQF+DPKGIox9oiAbohGHhK 5QU5o/NuOZmE52BcTILSZ3udjnYXDOuXRSAPqT5xOJPlbOfgqpqrNXFrAKLw2PPtsFJ/ nv/6SHHYaGHrRRBxWzvXdKuu6b5c7VGfHfAdE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:references:in-reply-to:mime-version :thread-index:date:message-id:subject:to:cc; bh=vp2VgWPwyteTcpK4z8LYtSq1k4hJe3CpyNPgePV5ru0=; b=YCOZka5IQFDNxWQZvnNk+2mm/oAOeKxjpZ8cs3Ts1Pp4r02HILinESZ6RFDp/sEKIu o7T5d7BwOzYR0nE5hO7WyPdgRTTHA5wk5+g3Xah+a5kFxoF0SPIGsFzAJvqLtI5bKWqs G2bS090FogSFbR8YrIytQNHA94odDqOSXcEFiyAjEiqLyszN53w681LcfuuNtTfZiUK7 u8arQXNr4XTResj5EvD7/1AfLlYBErjwPzmpVrmghlWk5+3bctXsfAuc/ranfT4zgoOQ 7SRJts6VqIEwT8w/rbna0mBNDj4sW4Ny29jAugl18QsZ1jnUhkZlC1mgXnNxZQW0hzpt 1S7w== X-Gm-Message-State: AOAM530vsNUcfcE2+baG1RvCyPZdxAilFK9XQclrkzCBd2lB47Yus6/T ebw1gHehqcuaJZVBxQxUX/76/Ag3gs73PnnId4XAPNO6y0I= X-Google-Smtp-Source: ABdhPJyHvNQ+c2OOK4dayy6nGlwQPW5zIP3LMw/zLAshnW0e2lGpMBJ/VUcX8dfuElb6aT+tlMppdx0bnOZK6ZoAZOg= X-Received: by 2002:a05:622a:1902:: with SMTP id w2mr10540984qtc.401.1639557953379; Wed, 15 Dec 2021 00:45:53 -0800 (PST) From: Kashyap Desai References: <20210906065003.439019-1-ming.lei@redhat.com> <0d8666c9983158a4954f30f6b429e797@mail.gmail.com> <86f2fb27dd6bc53fec3d8677c078937e@mail.gmail.com> In-Reply-To: MIME-Version: 1.0 X-Mailer: Microsoft Outlook 15.0 Thread-Index: AQCw9RdeG8B11ACtJOqN2MhOUMiBIQFcykQ1AY8PSusCS4w5QAGYevsErkqv0SA= Date: Wed, 15 Dec 2021 14:15:51 +0530 Message-ID: <3065cf1a25a99a2dd89e9065d679410e@mail.gmail.com> Subject: RE: [PATCH] blk-mq: avoid to iterate over stale request To: Ming Lei Cc: luojiaxing , Jens Axboe , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, "Martin K. Petersen" , John Garry Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="0000000000006a52b205d32b55d2" Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org --0000000000006a52b205d32b55d2 Content-Type: text/plain; charset="UTF-8" > > > > shared_tags->rqs[5] of hctx0 is having scmd = 0xAA (inflight command) > > shared_tags->rqs[10] of hctx0 is having scmd = 0xAA (inflight command) > > <- This is incorrect. While looping on hctx0 tags[], bitmap = 10 this > > entry is also found which is actually outstanding on hctx1. > > shared_tags->rqs[10] of hctx1 is having scmd = 0xBB (inflight command) > > Sorry, I am a bit confused, please look at the following code and > blk_mq_find_and_get_req()(<-bt_tags_iter). My issue is without shared tags. Below patch is certainly a fix for shared tags (for 5.16-rc). I have seen scsi eh deadlock issue on 5.15 kernel which does not have shared tags (but it has shared bitmap.) > > void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset, > busy_tag_iter_fn *fn, void *priv) { > unsigned int flags = tagset->flags; > int i, nr_tags; > > nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues; > > for (i = 0; i < nr_tags; i++) { > if (tagset->tags && tagset->tags[i]) > __blk_mq_all_tag_iter(tagset->tags[i], fn, priv, > BT_TAG_ITER_STARTED); > } > } > > In case of shared tags, only tagset->tags[0] is iterated over, so both > 5 and 10 are checked, and shared_tags->rqs[5] and shared_tags->rqs[10] > shouldn't just point to the two latest requests? How can both 0xAA & 0xBB be > retrieved from shared_tags->rqs[10]? Since I am not talking about shared tags, you can remap same condition now. In 5.15 kernel (shared bitmap is enabled but not shared tags) - blk_mq_tagset_busy_iter is called for each tags[] of nr_hw_queues times. It will call bt_tags_for_each() for hctx0.tags->[], hctx1.tags->[] .. Since tags->bitmap_tags is shared when it traverse hctx0.tags->[], it can find hctx0.tags[10].rq which is really stale entry. If the same request which is stale @ hctx0.tags[10] is really outstanding at some other tag#, stale entry will be counted in host_busy. > > > Issue noticed by me is the exact same issue described @ below - > > https://lore.kernel.org/linux-scsi/fe5cf6c4-ce5e-4a0f-f4ab-5c10539492c > > b@hu > > awei.com/ > > > > Issue is only exposed to shared host tagset. I got the required > > information. Thanks. > > > > Kashyap > > > > > > > count total 2 inflight commands instead of 1 from hctx0 context + > > > > From > > > > hctx1 context, we will count 1 inflight command = Total is 3. > > > > Even though we read after some delay, host_busy will be incorrect. > > > > We expect host_busy = 2 but it will return 3. > > > > > > > > This patch fix my issue explained above for shared host-tag case. > > > > I am confused reading the commit message. You may not have > > > > intentionally fix the issue as I explained but indirectly it fixes > > > > my issue. Am I > > correct ? > > > > > > > > What was an issue reported by Luojiaxiang ? I am interested to > > > > know if issue reported by Luojiaxiang had shared host tagset enabled ? > > > > > > https://lore.kernel.org/linux-scsi/fe5cf6c4-ce5e-4a0f-f4ab- > > > 5c10539492cb@huawei.com/ > > > > I check this. It is same issue as what I am seeing on Broadcom > > controller only if shared host tagset is enabled. > > But 67f3b2f822b7 ("blk-mq: avoid to iterate over stale request") isn't only for > shared tags. I mean, shared bitmap in my whole discussion. Megaraid_sas driver use shared bitmap, so it is exposed and It is confirmed from this discussion. Do we still have exposure (if "blk-mq: avoid to iterate over stale request" is not part of kernel) to mpi3mr type driver which does not use shared bitmap but has nr_hw_queues > 1. ? 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