From nobody Sat Jul 25 01:35:28 2026 Received: from mailgw.kylinos.cn (mailgw.kylinos.cn [124.126.103.232]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AD442214A9B; Wed, 22 Jul 2026 03:19:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=124.126.103.232 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784690375; cv=none; b=s2NQmYf0BV8Del6FOO+IgBFfUmGJqAxLKbWn0i8HQxox79jp6nLz5L/qgEf0v4IwUXBGM2uvlKgFAfUDoiGhmZyleS2MCAYWzYkLQSKfI8un+WLNh3N/xiR+Q3nou+57HTb3zuOxXN7PvvkQQrcI5GKl2nwA+5OCZHReMkGMVis= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784690375; c=relaxed/simple; bh=nDf+vYOIeQDAMqzBUMHPkjbOGcT3WO3h0OAi7R/XQb8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=fcKC+ikVtcGYsek11gOPPr/NlbzEsXt1gxfPcVJdlZJLooFMuvA+kVU6A3YFnvLTLJdPbN5zXo/qnhrQLh7AR87Tvn5wKlETBXKGtlBI9DxQ/4KlSaHGac02S3H9aTeBAOCqDQWMPRdAyXSBJCJce1Z4QEx9rt/3Y/cS47cCoR4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn; spf=pass smtp.mailfrom=kylinos.cn; arc=none smtp.client-ip=124.126.103.232 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kylinos.cn X-UUID: 22b0a204857c11f1aa26b74ffac11d73-20260722 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.3.12,REQID:39252bc1-79fe-456e-9a2c-c7cfc5b5d928,IP:0,U RL:0,TC:0,Content:0,EDM:0,RT:0,SF:0,FILE:0,BULK:0,RULE:Release_Ham,ACTION: release,TS:0 X-CID-META: VersionHash:e7bac3a,CLOUDID:91a7fb767f8edd80604abc8f2047e50e,BulkI D:nil,BulkQuantity:0,Recheck:0,SF:102|865|898,TC:nil,Content:0|15|50,EDM:- 3,IP:nil,URL:0,File:nil,RT:nil,Bulk:nil,QS:nil,BEC:nil,COL:0,OSI:0,OSA:0,A V:0,LES:1,SPR:NO,DKR:0,DKP:0,BRR:0,BRE:0,ARC:0 X-CID-BVR: 2,SSN|SDN X-CID-BAS: 2,SSN|SDN,0,_ X-CID-FACTOR: TF_CID_SPAM_SNR X-CID-RHF: D41D8CD98F00B204E9800998ECF8427E X-UUID: 22b0a204857c11f1aa26b74ffac11d73-20260722 X-User: liuxixin@kylinos.cn Received: from [127.0.1.1] [(10.44.16.150)] by mailgw.kylinos.cn (envelope-from ) (Generic MTA with TLSv1.3 TLS_AES_256_GCM_SHA384 256/256) with ESMTP id 1772511243; Wed, 22 Jul 2026 11:19:22 +0800 From: Xixin Liu To: linux-block@vger.kernel.org Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, liuxixin@kylinos.cn Subject: [PATCH v1] block/mq-deadline: hold elevator_lock in debugfs next_rq show Date: Tue, 21 Jul 2026 14:30:32 +0800 Message-ID: <2e689b2c4021.1784615432.git.liuxixin@kylinos.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Mailer: patches/scripts/send-local.py Content-Type: text/plain; charset="utf-8" deadline_*_next_rq_show() dereferences q->elevator->elevator_data without holding elevator_lock. Concurrent elevator switch to "none" clears q->elevator under that lock and tears down the scheduler, so readers crash with a null-ptr-deref. Hold elevator_lock around the show path and bail out if the elevator has already been removed, matching other blk-mq debugfs readers that look at elevator state. Reproduced on linux-next with KASAN by reading write1_next_rq via debugfs while switching the elevator from mq-deadline to none under fio load: BUG: KASAN: null-ptr-deref in deadline_write1_next_rq_show+0x3c/0xf0 Read of size 8 at addr 0000000000000010 by task cat/140857 Call trace: deadline_write1_next_rq_show+0x3c/0xf0 blk_mq_debugfs_show+0x58/0x78 seq_read_iter+0x254/0x6f8 seq_read+0x1a0/0x220 vfs_read+0x14c/0x528 Signed-off-by: Xixin Liu --- block/mq-deadline.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/block/mq-deadline.c b/block/mq-deadline.c index 824bfc17b2c6..e7c4a91b2d08 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -842,14 +842,22 @@ static int deadline_##name##_next_rq_show(void *data,= \ struct seq_file *m) \ { \ struct request_queue *q =3D data; \ - struct deadline_data *dd =3D q->elevator->elevator_data; \ - struct dd_per_prio *per_prio =3D &dd->per_prio[prio]; \ + struct elevator_queue *e; \ + struct deadline_data *dd; \ + struct dd_per_prio *per_prio; \ struct request *rq; \ + int ret; \ \ + ret =3D mutex_lock_interruptible(&q->elevator_lock); \ + if (ret) \ + return ret; \ + e =3D q->elevator; \ + if (!e) \ + goto unlock; \ + dd =3D e->elevator_data; \ + per_prio =3D &dd->per_prio[prio]; \ rq =3D deadline_from_pos(per_prio, data_dir, \ per_prio->latest_pos[data_dir]); \ if (rq) \ __blk_mq_debugfs_rq_show(m, rq); \ +unlock: \ + mutex_unlock(&q->elevator_lock); \ return 0; \ } =20 --=20 2.43.0