From patchwork Tue Aug 15 06:04:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chengming Zhou X-Patchwork-Id: 13353553 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 49D7EC001B0 for ; Tue, 15 Aug 2023 06:07:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235057AbjHOGH1 (ORCPT ); Tue, 15 Aug 2023 02:07:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41110 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235090AbjHOGGq (ORCPT ); Tue, 15 Aug 2023 02:06:46 -0400 X-Greylist: delayed 137961 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Mon, 14 Aug 2023 23:05:43 PDT Received: from out-74.mta1.migadu.com (out-74.mta1.migadu.com [IPv6:2001:41d0:203:375::4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14FF530DA for ; Mon, 14 Aug 2023 23:05:42 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1692079529; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=wWsB6kltJ58XUaHsFfqL6Q4RJBmpJEQuaQ5cbRsruY0=; b=NUHbtoXEkOC8aBNe94FABWlMwijvoLrxPXdAz3cp2t7x8mszPyYnRShHVoRdYT3qPD5tLB +t02N9eyMZwIdEVE0NAV0OYK/eOF+laBK0+x0X9i+s1cJD4ynQ8cAhQyrn2ia3XJBfoZ/v /D2RPLbW1RgSe4Az0tdTxRbZd0eUSZw= From: chengming.zhou@linux.dev To: axboe@kernel.dk, kch@nvidia.com, dhowells@redhat.com Cc: damien.lemoal@opensource.wdc.com, bvanassche@acm.org, nj.shetty@samsung.com, kbusch@kernel.org, zhouchengming@bytedance.com, akinobu.mita@gmail.com, shinichiro.kawasaki@wdc.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] null_blk: fix poll request timeout handling Date: Tue, 15 Aug 2023 14:04:42 +0800 Message-ID: <20230815060443.660263-1-chengming.zhou@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org From: Chengming Zhou When doing io_uring benchmark on /dev/nullb0, it's easy to crash the kernel if poll requests timeout triggered, as reported by David. [1] BUG: kernel NULL pointer dereference, address: 0000000000000008 Workqueue: kblockd blk_mq_timeout_work RIP: 0010:null_timeout_rq+0x4e/0x91 Call Trace: ? __die_body+0x1a/0x5c ? page_fault_oops+0x6f/0x9c ? kernelmode_fixup_or_oops+0xc6/0xd6 ? __bad_area_nosemaphore+0x44/0x1eb ? exc_page_fault+0xe2/0xf4 ? asm_exc_page_fault+0x22/0x30 ? null_timeout_rq+0x4e/0x91 blk_mq_handle_expired+0x31/0x4b bt_iter+0x68/0x84 ? bt_tags_iter+0x81/0x81 __sbitmap_for_each_set.constprop.0+0xb0/0xf2 ? __blk_mq_complete_request_remote+0xf/0xf bt_for_each+0x46/0x64 ? __blk_mq_complete_request_remote+0xf/0xf ? percpu_ref_get_many+0xc/0x2a blk_mq_queue_tag_busy_iter+0x14d/0x18e blk_mq_timeout_work+0x95/0x127 process_one_work+0x185/0x263 worker_thread+0x1b5/0x227 ? rescuer_thread+0x287/0x287 kthread+0xfa/0x102 ? kthread_complete_and_exit+0x1b/0x1b ret_from_fork+0x22/0x30 This is indeed a race problem between null_timeout_rq() and null_poll(). null_poll() null_timeout_rq() spin_lock(&nq->poll_lock) list_splice_init(&nq->poll_list, &list) spin_unlock(&nq->poll_lock) while (!list_empty(&list)) req = list_first_entry() list_del_init() ... blk_mq_add_to_batch() // req->rq_next = NULL spin_lock(&nq->poll_lock) // rq->queuelist->next == NULL list_del_init(&rq->queuelist) spin_unlock(&nq->poll_lock) What's worse is that we don't call blk_mq_complete_request_remote() before blk_mq_add_to_batch(), so these completed requests have wrong rq->state == MQ_RQ_IN_FLIGHT. We can easily check this using bpftrace: ``` bpftrace -e 'kretfunc:null_blk:null_poll { $iob=(struct io_comp_batch *)args->iob; @[$iob->req_list->state]=count(); }' @[1]: 51708 ``` Fix these problems by setting requests state to MQ_RQ_COMPLETE under nq->poll_lock protection, in which null_timeout_rq() can safely detect this race and early return. [1] https://lore.kernel.org/all/3893581.1691785261@warthog.procyon.org.uk/ Fixes: 0a593fbbc245 ("null_blk: poll queue support") Reported-by: David Howells Signed-off-by: Chengming Zhou Tested-by: David Howells Reviewed-by: Ming Lei --- drivers/block/null_blk/main.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c index 864013019d6b..968090935eb2 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -1643,9 +1643,12 @@ static int null_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob) struct nullb_queue *nq = hctx->driver_data; LIST_HEAD(list); int nr = 0; + struct request *rq; spin_lock(&nq->poll_lock); list_splice_init(&nq->poll_list, &list); + list_for_each_entry(rq, &list, queuelist) + blk_mq_set_request_complete(rq); spin_unlock(&nq->poll_lock); while (!list_empty(&list)) { @@ -1671,16 +1674,21 @@ static enum blk_eh_timer_return null_timeout_rq(struct request *rq) struct blk_mq_hw_ctx *hctx = rq->mq_hctx; struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq); - pr_info("rq %p timed out\n", rq); - if (hctx->type == HCTX_TYPE_POLL) { struct nullb_queue *nq = hctx->driver_data; spin_lock(&nq->poll_lock); + /* The request may have completed meanwhile. */ + if (blk_mq_request_completed(rq)) { + spin_unlock(&nq->poll_lock); + return BLK_EH_DONE; + } list_del_init(&rq->queuelist); spin_unlock(&nq->poll_lock); } + pr_info("rq %p timed out\n", rq); + /* * If the device is marked as blocking (i.e. memory backed or zoned * device), the submission path may be blocked waiting for resources