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 X-Spam-Level: X-Spam-Status: No, score=-4.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE741C433ED for ; Tue, 4 May 2021 21:18:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F57F610C8 for ; Tue, 4 May 2021 21:18:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232840AbhEDVTS (ORCPT ); Tue, 4 May 2021 17:19:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:33552 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232803AbhEDVTS (ORCPT ); Tue, 4 May 2021 17:19:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPS id A9F95613C6 for ; Tue, 4 May 2021 21:18:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620163102; bh=SlQWr+q+QcZivMulldFb6jYEHQQ6HC/NeIk8zBuK49Q=; h=From:To:Subject:Date:In-Reply-To:References:From; b=JQ48u2QFYlk2Zz/6YscnrvEIyk8f8OEJfqnqFTmm4kvxbxToOOrsBT5bceMCVIBtM eiBVRpPRSYl8YjekwdGNqvmf4gQBSRFOYds1/iQ1fWjE3nbx4lk+wxYE6co4Ni5OKt j8E1yY7i7zCyOFVJCmtMkpOYBIxdOjLT1b0vToa6JPuFFBHKfw9bz2d2Wp/zxglid+ JVR3VPLEELFZe9uVPK34P3o7uPbM+OIFPh9jDvT1gOzvRA1WHnHMnLCzNftA6pSdYH BXWiAS97Y0qn2QTBx5ZsXhEkDkNFIKTqZeK/GRV0e6tNK3MXhxNaguBaZIyh10hCPE zs+fjQspcbs5w== From: bugzilla-daemon@bugzilla.kernel.org To: linux-scsi@vger.kernel.org Subject: [Bug 212337] scsi_debug: race at module load and module unload Date: Tue, 04 May 2021 21:18:22 +0000 X-Bugzilla-Reason: None X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: AssignedTo scsi_drivers-other@kernel-bugs.osdl.org X-Bugzilla-Product: SCSI Drivers X-Bugzilla-Component: Other X-Bugzilla-Version: 2.5 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: mcgrof@kernel.org X-Bugzilla-Status: REOPENED X-Bugzilla-Resolution: X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: scsi_drivers-other@kernel-bugs.osdl.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_status resolution Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugzilla.kernel.org/ Auto-Submitted: auto-generated MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org https://bugzilla.kernel.org/show_bug.cgi?id=3D212337 Luis Chamberlain (mcgrof@kernel.org) changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |REOPENED Resolution|WILL_NOT_FIX |--- --- Comment #13 from Luis Chamberlain (mcgrof@kernel.org) --- (In reply to d gilbert from comment #12) > On 2021-03-22 12:23 p.m., bugzilla-daemon@bugzilla.kernel.org wrote: > > https://bugzilla.kernel.org/show_bug.cgi?id=3D212337 > >=20 > > --- Comment #9 from Luis Chamberlain (mcgrof@kernel.org) --- > > (In reply to d gilbert from comment #8) > >=20 > >>>> The scsi_debug module option that is already in place is: > >>>> tur_ms_to_ready: TEST UNIT READY millisecs before initial good > status > >>>> (def=3D0) > >> > >> You asked how it works, try: > >> modprobe scsi_debug tur_ms_to_ready=3D20000 > >> > >=20 > > That does not resolve the rmmod race against insmod: > >=20 > > scsi host2: scsi_debug: version 0190 [20200710] > > [ 42.213400] dev_size_mb=3D8, opts=3D0x0, submit_queues=3D1, statis= tics=3D0 > > [ 42.217527] scsi 2:0:0:0: Direct-Access Linux scsi_debug=20= =20=20=20=20=20 > 0190 > > PQ: 0 ANSI: 7 > > [ 42.223346] scsi 2:0:0:0: Attached scsi generic sg0 type 0 > > [ 42.282195] scsi host2: scsi_debug: version 0190 [20200710] > > [ 42.282195] dev_size_mb=3D8, opts=3D0x0, submit_queues=3D1, statis= tics=3D0 > > [ 42.288169] scsi 2:0:0:0: Direct-Access Linux scsi_debug=20= =20=20=20=20=20 > 0190 > > PQ: 0 ANSI: 7 > > [ 42.292122] sd 2:0:0:0: Attached scsi generic sg0 type 0 > > [ 42.292244] sd 2:0:0:0: Power-on or device reset occurred > > [ 42.302288] sd 2:0:0:0: [sda] Spinning up disk... > >=20 > > Then we wait... > >=20 > > [ 44.308213] ...................ready > > [ 62.748919] sd 2:0:0:0: [sda] 16384 512-byte logical blocks: (8.39 > MB/8.00 > > MiB) > > [ 62.754265] sd 2:0:0:0: [sda] Write Protect is off > > [ 62.763253] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enab= led, > > supports DPO and FUA > > [ 62.776965] sd 2:0:0:0: [sda] Optimal transfer size 524288 bytes > > [ 62.883817] sd 2:0:0:0: [sda] Attached SCSI disk > >=20 > > And then rmmod still fails. > >=20 >=20 > Just to explain a bit more about tur_ms_to_ready, that does not effect SC= SI > commands like REPORT LUNS, INQUIRY and REQUEST SENSE, but does slow down = all > "media access" commands including TEST UNIT READY (TUR) and READ CAPACITY= . So > if you watch what is happening with 'lsscsi -s' the device (LUN) will app= ear > almost immediately but its size will be "-" due to the fact that READ > CAPACITY (or TUR before it) is waiting for tur_ms_to_ready to elapse. Aft= er > that the size (for disks) will be shown by 'lsscsi -s'. >=20 >=20 > When you say 'rmmod still fails' do you mean it refuses to remove the mod= ule > because the device is busy? Yes. The refcnt must be 1 for rmmod to work. If it is not it will fail. > If is busy, where is the race?. What precisely > would you like to happen? What does a real SCSI HBA do? That's the thing, the trace on comment #1 does not exactly show who to blam= e, but there seems to be only two possibilities: systemd and multipath. Regard= less what is clearer is that once the device is exposed we *cannot* block usersp= ace from poking at the device. The best we can do, is udevadm settle, however t= hat still does not guarantee userspace things like multipath won't try to poke. > Is there any way that a driver can detect that rmmod has been called and > rejected? Yes! try_module_get() would fail if rmmod was kicked off. > If not, we could add a "shutdown" writable attribute in > /sys/bus/pseudo/drivers/scsi_debug/ . Then if a large number of pseudo > devices is being built due to the modprobe invocation, the driver can go > into reverse by checking that attribute before it adds another host > (target or LUN?). After shutdown, the driver is still active, just with > no hosts, and thus no LUNs. A more accurate name would be rm_all_hosts . This may work actually, and so new users who would want to avoid this race would have to issue this call prior to rmmod. That would remove the possibi= lity of a race. Let me know if you have a patch I can test. Putting this as re-opened. --=20 You may reply to this email to add a comment. 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