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 457FAC32771 for ; Wed, 21 Sep 2022 09:59:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229678AbiIUJ73 (ORCPT ); Wed, 21 Sep 2022 05:59:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48524 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229588AbiIUJ72 (ORCPT ); Wed, 21 Sep 2022 05:59:28 -0400 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6035F8A7CB; Wed, 21 Sep 2022 02:59:26 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=ziyangzhang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VQNuD5g_1663754358; Received: from localhost.localdomain(mailfrom:ZiyangZhang@linux.alibaba.com fp:SMTPD_---0VQNuD5g_1663754358) by smtp.aliyun-inc.com; Wed, 21 Sep 2022 17:59:24 +0800 From: ZiyangZhang To: ming.lei@redhat.com Cc: axboe@kernel.dk, xiaoguang.wang@linux.alibaba.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, joseph.qi@linux.alibaba.com, ZiyangZhang Subject: [PATCH V4 0/8] ublk_drv: add USER_RECOVERY support Date: Wed, 21 Sep 2022 17:58:41 +0800 Message-Id: <20220921095849.84988-1-ZiyangZhang@linux.alibaba.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org ublk_drv is a driver simply passes all blk-mq rqs to userspace target(such as ublksrv[1]). For each ublk queue, there is one ubq_daemon(pthread). All ubq_daemons share the same process which opens /dev/ublkcX. The ubq_daemon code infinitely loops on io_uring_enter() to send/receive io_uring cmds which pass information of blk-mq rqs. Since the real IO handler(the process/thread opening /dev/ublkcX) is in userspace, it could crash if: (1) the user kills -9 it because of IO hang on backend, system reboot, etc... (2) the process/thread catches a exception(segfault, divisor error, oom...) Therefore, the kernel driver has to deal with a dying ubq_daemon or the process. Now, if one ubq_daemon(pthread) or the process crashes, ublk_drv must abort the dying ubq, stop the device and release everything. This is not a good choice in practice because users do not expect aborted requests, I/O errors and a released device. They may want a recovery machenism so that no requests are aborted and no I/O error occurs. Anyway, users just want everything works as usual. This patchset implements USER_RECOVERY support. If the process or any ubq_daemon(pthread) crashes(exits accidentally), we allow user to provide new process and ubq_daemons. Note: The responsibility of recovery belongs to the user who opens /dev/ublkcX. After a crash, the kernel driver only switch the device's state to be ready for recovery(START_USER_RECOVERY) or termination(STOP_DEV). The state is defined as UBLK_S_DEV_QUIESCED. This patchset does not provide how to detect such a crash in userspace. The user has may ways to do so. For example, user may: (1) send GET_DEV_INFO on specific dev_id and check if its state is UBLK_S_DEV_QUIESCED. (2) 'ps' on ublksrv_pid. Recovery feature is quite useful for real products. In detail, we support this scenario: (1) The /dev/ublkc0 is opened by process 0. (2) Fio is running on /dev/ublkb0 exposed by ublk_drv and all rqs are handled by process 0. (3) Process 0 suddenly crashes(e.g. segfault); (4) Fio is still running and submit IOs(but these IOs cannot be dispatched now) (5) User starts process 1 and attach it to /dev/ublkc0 (6) All rqs are handled by process 1 now and IOs can be completed now. Note: The backend must tolerate double-write because we re-issue a rq sent to the old process 0 before. We provide a sample script here to simulate the above steps: ***************************script*************************** LOOPS=10 __ublk_get_pid() { pid=`./ublk list -n 0 | grep "pid" | awk '{print $7}'` echo $pid } ublk_recover_kill() { for CNT in `seq $LOOPS`; do dmesg -C pid=`__ublk_get_pid` echo -e "*** kill $pid now ***" kill -9 $pid sleep 6 echo -e "*** recover now ***" ./ublk recover -n 0 sleep 6 done } ublk_test() { echo -e "*** add ublk device ***" ./ublk add -t null -d 4 -i 1 sleep 2 echo -e "*** start fio ***" fio --bs=4k \ --filename=/dev/ublkb0 \ --runtime=140s \ --rw=read & sleep 4 ublk_recover_kill wait echo -e "*** delete ublk device ***" ./ublk del -n 0 } for CNT in `seq 4`; do modprobe -rv ublk_drv modprobe ublk_drv echo -e "************ round $CNT ************" ublk_test sleep 5 done ***************************script*************************** You may run it with our modified ublksrv[2] which supports recovery feature. No I/O error occurs and you can verify it by typing $ perf-tools/bin/tpoint block:block_rq_error The basic idea of USER_RECOVERY is quite straightfoward: (1) quiesce ublk queues and requeue/abort rqs. (2) release/free everything belongs to the dying process. Note: Since ublk_drv does save information about user process, this work is important because we don't expect any resource lekage. Particularly, ioucmds from the dying ubq_daemons need to be completed(freed). (3) allow new ubq_daemons issue FETCH_REQ. Note: ublk_ch_uring_cmd() checks some states and flags. We have to set them to a correct value. Here is steps to reocver: (0) requests dispatched after the corresponding ubq_daemon is dying are requeued. (1) monitor_work finds one dying ubq_daemon, and it should schedule quiesce_work and requeue/abort requests issued to userspace before the ubq_daemon is dying. (2) quiesce_work must (a)quiesce request queue to ban any incoming ublk_queue_rq(), (b)wait unitl all rqs are IDLE, (c)complete old ioucmds. Then the ublk device is ready for recovery or stop. (3) Since io_uring resources are released, ublk_ch_release() is called and all ublk_ios are reset to be ready for a new process. (4) Then, user should start a new process and ubq_daemons(pthreads) and send FETCH_REQ by io_uring_enter() to make all ubqs be ready. The user must correctly setup queues, flags and so on(how to persist user's information is not related to this patchset). (6) The user sends RESTART_DEV ctrl-cmd to /dev/ublk-control with a dev_id X. (7) After receiving RESTART_DEV, ublk_drv waits for all ubq_daemons getting ready. Then it unquiesces request queue and new rqs are allowed. You should use ublksrv[2] and tests[3] provided by us. We add 3 additional tests to verify that recovery feature works. Our code will be PR-ed to Ming's repo soon. [1] https://github.com/ming1/ubdsrv [2] https://github.com/old-memories/ubdsrv/tree/recovery-v1 [3] https://github.com/old-memories/ubdsrv/tree/recovery-v1/tests/generic Since V3: (1) do not kick requeue list in ublk_queue_rq() or io_uring fallback wq with a dying ubq_daemon but kicking the list once while unquiescing dev (2) add comment on requeing rqs in ublk_queue_rq(), or io_uring fallback wq with a dying ubq_daemon (3) split support for UBLK_F_USER_RECOVERY_REISSUE into a single patch (4) let monitor_work abort/requeue rqs issued to userspace instead of quiesce_work with recovery enabled (5) alway wait until no INFLIGHT rq exists in ublk_quiesce_dev() (6) move ublk re-init stuff into ublk_ch_release() (7) let ublk_quiesce_dev() go on as long as one ubq_daemon is dying (8) add only one ctrl-cmd and rename it as RESTART_DEV (9) check ub.dev_info->flags instead of iterating on all ubqs (10) do not disable recoevry feature, but always qiuesce dev in ublk_stop_dev() and then unquiesce it (11) add doc on USER_RECOVERY feature Since V2: (1) run ublk_quiesce_dev() in a standalone work. (2) do not run monitor_work after START_USER_RECOVERY is handled. (3) refactor recovery feature code so that it does not affect current code. Since V1: (1) refactor cover letter. Add intruduction on "how to detect a crash" and "why we need recovery feature". (2) do not refactor task_work and ublk_queue_rq(). (3) allow users freely stop/recover the device. (4) add comment on ublk_cancel_queue(). (5) refactor monitor_work and aborting machenism since we add recovery machenism in monitor_work. ZiyangZhang (8): ublk_drv: check 'current' instead of 'ubq_daemon' ublk_drv: refactor ublk_cancel_queue() ublk_drv: define macros for recovery feature and check them ublk_drv: requeue rqs with recovery feature enabled ublk_drv: consider recovery feature in aborting mechanism ublk_drv: support UBLK_F_USER_RECOVERY_REISSUE ublk_drv: allow new process to open ublk chardev with recovery feature enabled Documentation: document ublk user recovery feature Documentation/block/ublk.rst | 25 +++ drivers/block/ublk_drv.c | 345 +++++++++++++++++++++++++++++++--- include/uapi/linux/ublk_cmd.h | 6 + 3 files changed, 354 insertions(+), 22 deletions(-) -- 2.27.0