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 7B0DAC433FE for ; Thu, 3 Nov 2022 03:53:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231290AbiKCDxo (ORCPT ); Wed, 2 Nov 2022 23:53:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231269AbiKCDxE (ORCPT ); Wed, 2 Nov 2022 23:53:04 -0400 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8EE0D19C39; Wed, 2 Nov 2022 20:51:19 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4N2qVh3gYgz6PDHf; Thu, 3 Nov 2022 11:48:44 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP2 (Coremail) with SMTP id Syh0CgAnDtO0OmNjIRYaBQ--.12160S3; Thu, 03 Nov 2022 11:51:17 +0800 (CST) Subject: Re: [RFC PATCH] bfq: fix waker_bfqq inconsistency crash To: Khazhy Kumykov , Yu Kuai Cc: Paolo Valente , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, "yukuai (C)" , Jan Kara References: <20221103013937.603626-1-khazhy@google.com> <3c0df3fa-8731-5863-ccc5-f2e60601dbf9@huaweicloud.com> From: Yu Kuai Message-ID: Date: Thu, 3 Nov 2022 11:51:15 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: Syh0CgAnDtO0OmNjIRYaBQ--.12160S3 X-Coremail-Antispam: 1UD129KBjvJXoW7Aw17CFyrtFWrKry7uryDWrg_yoW8Zr15p3 y0gFWjgr4xJrySgrZFyw4UAFyFvr4rWrZ8KryYg3s7ArZ8Ga4xtFsFkw4ruayfGFZ3K3ZI vr1Fqa45Gr1DAaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkE14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7I2V7IY0VAS07AlzVAY IcxG8wCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14 v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkG c2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI 0_Jr0_Gr1lIxAIcVCF04k26cxKx2IYs7xG6rWUJVWrZr1UMIIF0xvEx4A2jsIE14v26r1j 6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0JUdHU DUUUUU= X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, 在 2022/11/03 11:05, Khazhy Kumykov 写道: > On Wed, Nov 2, 2022 at 7:56 PM Yu Kuai wrote: >> >> Hi, >> >> 在 2022/11/03 9:39, Khazhismel Kumykov 写道: >>> 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 >> >> From what I see, bfqq->waker_bfqq is updated in bfq_init_rq() only if >> 'new_queue' is false, but if 'new_queue' is false, the returned 'bfqq' >> from bfq_get_bfqq_handle_split() will never be oom_bfqq, so I'm confused >> here... > There's two calls for bfq_get_bfqq_handle_split in this function - the > second one is after the check you mentioned, and is the problematic > one. Yes, thanks for the explanation. Now I understand how the problem triggers. >> >>> 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. >> >> Once oom_bfqq is used, I think the io is treated as issued from root >> group. Hence I don't think it's necessary to set woken_list or >> waker_bfqq for oom_bfqq. > Ack, I was wondering what's right here since, evidently, *someone* had > already set oom_bfqq->waker_bfqq to *something* (although... maybe it > was an earlier init_rq). But maybe it's better to do nothing if we > *know* it's oom_bfqq. I need to have a check how oom_bfqq get involved with waker_bfqq, and then see if it's reasonable. Probably Jan and Paolo will have better view on this. Thanks, Kuai > > Is it a correct interpretation here that setting waker_bfqq won't > accomplish anything anyways on oom_bfqq, so better off not?