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[2620:137:e000::1:20]) by mx.google.com with ESMTP id ca7-20020aa7cd67000000b0045caa8bf80bsi15232098edb.307.2022.11.02.19.00.01; Wed, 02 Nov 2022 19:00:27 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@chromium.org header.s=google header.b="a/RROOv1"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chromium.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230303AbiKCBki (ORCPT + 99 others); Wed, 2 Nov 2022 21:40:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44118 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229459AbiKCBkf (ORCPT ); Wed, 2 Nov 2022 21:40:35 -0400 Received: from mail-pl1-x62e.google.com (mail-pl1-x62e.google.com [IPv6:2607:f8b0:4864:20::62e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 09F441114D for ; Wed, 2 Nov 2022 18:40:34 -0700 (PDT) Received: by mail-pl1-x62e.google.com with SMTP id v17so555954plo.1 for ; Wed, 02 Nov 2022 18:40:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=EvT5dgXSYKBpxcVTYD1qf8cSHTUWaJZF8xGQfaZD+ZU=; b=a/RROOv1Lf+Wm2fr9D3eQRp6ISUL4AOlQae9HPGthkEBzMVudH/Ngx9bXGynny5St8 g0gYbfl3i3N9mbrpII9cqdelc6e1jWDzwrnmemcXg1eQTOPVbzFlUqRFvUfpWh4Ma511 97Sta3HSo6BKDK7nmnjJrX5BWxK3RqZtOqATk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=EvT5dgXSYKBpxcVTYD1qf8cSHTUWaJZF8xGQfaZD+ZU=; b=opeFk1AxNcC3bBrLKCxzm13aauOiJg84aTocKzcatr7dlBIhUc+E++RRzkxhC/ofiM tUYze0b+/PpqbuY+r1hyQlSg6GkhTRvJo63sMO8Wie4uWT3Q9CcTQ22OcfATf6o6SARr vVltvkq6HRp+L+dLYZQNMj41lef279ylqaDNbFZUIZYrgNnToiaRFNkxqxwByF8fFcV/ ncP9yUqYtbdj8mRO4AdsibNuOntJzaZ0u/cQ1n3phENNa8QrtEEOOEyTGRw8sr6xr4Ji PoTXzAWUTpmmB8QqBt49Wydxx+IHUJZq6d2dpoLADFwE9TbHvhcNQWYyPzl0C8OrJYjo CCyA== X-Gm-Message-State: ACrzQf2b5OaqGNclKfW+MMCc/WH3Gj8xVXdjxs7kqGJvLJvBYLj9S0CN CntG+6rMyhtZ1Iw1o6LOJ5l/bA== X-Received: by 2002:a17:90a:2a02:b0:214:247a:c185 with SMTP id i2-20020a17090a2a0200b00214247ac185mr8234172pjd.226.1667439633589; Wed, 02 Nov 2022 18:40:33 -0700 (PDT) Received: from khazhy-linux.svl.corp.google.com ([2620:15c:2d4:203:1464:23cb:dead:55d3]) by smtp.gmail.com with ESMTPSA id x8-20020a17090abc8800b0020ad86f4c54sm2091370pjr.16.2022.11.02.18.40.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Nov 2022 18:40:33 -0700 (PDT) From: Khazhismel Kumykov X-Google-Original-From: Khazhismel Kumykov To: Paolo Valente , Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Khazhismel Kumykov Subject: [RFC PATCH] bfq: fix waker_bfqq inconsistency crash Date: Wed, 2 Nov 2022 18:39:37 -0700 Message-Id: <20221103013937.603626-1-khazhy@google.com> X-Mailer: git-send-email 2.38.1.273.g43a17bfeac-goog MIME-Version: 1.0 X-Spam-Status: No, score=-3.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748438433438530545?= X-GMAIL-MSGID: =?utf-8?q?1748438433438530545?= This fixes crashes in bfq_add_bfqq_busy due to waker_bfqq being NULL, but woken_list_node still being hashed. This would happen when bfq_init_rq() expects a brand new allocated queue to be returned from bfq_get_bfqq_handle_split() and unconditionally updates waker_bfqq without resetting woken_list_node. Since we can always return oom_bfqq when attempting to allocate, we cannot assume waker_bfqq starts as NULL. We must either reset woken_list_node, or avoid setting woken_list at all for oom_bfqq - opt to do the former. Crashes would have a stacktrace like: [160595.656560] bfq_add_bfqq_busy+0x110/0x1ec [160595.661142] bfq_add_request+0x6bc/0x980 [160595.666602] bfq_insert_request+0x8ec/0x1240 [160595.671762] bfq_insert_requests+0x58/0x9c [160595.676420] blk_mq_sched_insert_request+0x11c/0x198 [160595.682107] blk_mq_submit_bio+0x270/0x62c [160595.686759] __submit_bio_noacct_mq+0xec/0x178 [160595.691926] submit_bio+0x120/0x184 [160595.695990] ext4_mpage_readpages+0x77c/0x7c8 [160595.701026] ext4_readpage+0x60/0xb0 [160595.705158] filemap_read_page+0x54/0x114 [160595.711961] filemap_fault+0x228/0x5f4 [160595.716272] do_read_fault+0xe0/0x1f0 [160595.720487] do_fault+0x40/0x1c8 Tested by injecting random failures into bfq_get_queue, crashes go away completely. Fixes: 8ef3fc3a043c ("block, bfq: make shared queues inherit wakers") Signed-off-by: Khazhismel Kumykov --- RFC mainly because it's not clear to me the best policy here - but the patch is tested and fixes a real crash we started seeing in 5.15 This is following up my ramble over at https://lore.kernel.org/lkml/CACGdZYLMnfcqwbAXDx+x9vUOMn2cz55oc+8WySBS3J2Xd_q7Lg@mail.gmail.com/ block/bfq-iosched.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 7ea427817f7f..5d2861119d20 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6793,7 +6793,12 @@ static struct bfq_queue *bfq_init_rq(struct request *rq) * reset. So insert new_bfqq into the * woken_list of the waker. See * bfq_check_waker for details. + * + * Also, if we got oom_bfqq, we must check if + * it's already in a woken_list */ + if (unlikely(!hlist_unhashed(&bfqq->woken_list_node))) + hlist_del_init(&bfqq->woken_list_node); if (bfqq->waker_bfqq) hlist_add_head(&bfqq->woken_list_node, &bfqq->waker_bfqq->woken_list);