From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 A0AE314A8E; Thu, 25 Sep 2025 22:06:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758837965; cv=none; b=OMNCem88wDehPbgEx0eImF1F5K1mzjdTUYGQtVmJaBWivP4Y1vYhBX1X2gjSdHJ3pX9iucaIrpyTxbG2XdwnObwjobSzS0kCdFXzIG8fhuoNVR+3pVNQsx+tnXHMagQktKoK2shlqulg0nNQ/RALAymyGArdt83b9miAZZDRVJU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758837965; c=relaxed/simple; bh=dgahcYI50uIA6amKSI62BYH+n1qIuOu+Xr2tu6p9RJE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=l+q3LhwN6R34ts+nVMTtypPOPDG/UDl4ExzhAqn/ks17CCtMsch5O+iwIFokbpYyoFBgsVbDDKEjItSAbcc8ZJm7RDMWxZes7jW8p0G9S47IbtquS8xHJbmEEviYGyvA8hFMhAYCuGChqZvfJ62VDTCxOAQOSRL5qCQ1IzQT814= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=PcEXW0dK; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="PcEXW0dK" Received: from pps.filterd (m0356516.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 58PImKV2030005; Thu, 25 Sep 2025 22:05:57 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=K7IRn6 bG/6nky59M0Oo2KeM1fFNlrak9irHbIR1LLzI=; b=PcEXW0dKW/ZzIaNcLcP6o7 QAf48rO1q7z311g0AC5Ji40dVw5nhc8D9LbIyTUyZ0pvggELKOrFl/gTeNQ7rxRC YfQiiBjLbYlr4hZ/T3iQ2Kg2kYFlIlizRospe55sblNmyXKLl2wac0dIHUfNEGCK peypBAhhnfb3HKH87DGXggWcnp4mTqb2bK/1iZb7eYfe3O6Hm/tE57GwVJ/zv4tK mVSwQVEndzrDq/Wq6vfROPOBv4ZrOgXuebdJ1mjGhB6Xi0phE4/7Mis0gAEwDFfi SVnxm7bbngxZjdhcEViue/Mph4XrkU5Yi9RYIWuFPrqcPKaZChFFelZIisVK71wg == Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 49dbbagwe4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 25 Sep 2025 22:05:57 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 58PLe3sj014307; Thu, 25 Sep 2025 22:05:56 GMT Received: from smtprelay06.dal12v.mail.ibm.com ([172.16.1.8]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 49dawm0yue-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 25 Sep 2025 22:05:56 +0000 Received: from smtpav04.wdc07v.mail.ibm.com (smtpav04.wdc07v.mail.ibm.com [10.39.53.231]) by smtprelay06.dal12v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 58PM5twN25952884 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Sep 2025 22:05:55 GMT Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8F40158050; Thu, 25 Sep 2025 22:05:55 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 13D9258045; Thu, 25 Sep 2025 22:05:54 +0000 (GMT) Received: from [9.61.254.10] (unknown [9.61.254.10]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 25 Sep 2025 22:05:53 +0000 (GMT) Message-ID: <82ab0e33-43ab-4b65-b24f-9ea83a859d62@linux.ibm.com> Date: Thu, 25 Sep 2025 15:05:43 -0700 Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] PCI/IOV: Add missing PCI rescan-remove locking when enabling/disabling SR-IOV To: Niklas Schnelle , Bjorn Helgaas , Lukas Wunner Cc: Keith Busch , Gerd Bayer , Matthew Rosato , Benjamin Block , Halil Pasic , Julian Ruess , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250826-pci_fix_sriov_disable-v1-0-2d0bc938f2a3@linux.ibm.com> <20250826-pci_fix_sriov_disable-v1-1-2d0bc938f2a3@linux.ibm.com> <9fb43fc399ac5917605b7bc721c4b0affb8ca255.camel@linux.ibm.com> Content-Language: en-US From: Farhan Ali In-Reply-To: <9fb43fc399ac5917605b7bc721c4b0affb8ca255.camel@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: N2eU3qL5PwiwqGVOyQl1CGnycvZfnP5l X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTI1MDE3NCBTYWx0ZWRfXywC3eHLPAczg bb+hIriYgiTrcBDlydpWi5pVIN5prxkyDLOoJ68BPNdsFBjDNodO6CY0apYMAPvSrC68RmR3MCQ w9SHZC7o1THHA6Z8F2PpXI2q2wlzpgDEthfgXUqv9lrtHGYk7a8UFfhb2G6MfC86O/Wbs2MmFm0 AJDJRt2soKtLGLZCGfDIu/fWsTNJ9o62s+TrVjSOEOX1yOYNKVr6DEo5ZTeu5pRwecWfTx+FoJF ywRxP6JcxaM42EsnxTza6OIbjPBzQpExq5VWWOMRXmeZ/PZe7bhAW/IpS2sEHmMbX54BePV8LoT mBvXXJwmKXGTErIhMfBX8pi0lTZ9bcmwKYIy5guS/TgdSnb6hw1KB3/DsyoP3Fra9IeD+fY8SC/ ca5x7p+z/I1tgBGJWncghW7z3IqEug== X-Proofpoint-ORIG-GUID: N2eU3qL5PwiwqGVOyQl1CGnycvZfnP5l X-Authority-Analysis: v=2.4 cv=B6W0EetM c=1 sm=1 tr=0 ts=68d5bcc5 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=f7japnTVbOoWgXTj3B8A:9 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-25_02,2025-09-25_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 spamscore=0 clxscore=1015 priorityscore=1501 phishscore=0 malwarescore=0 lowpriorityscore=0 adultscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2509150000 definitions=main-2509250174 On 9/25/2025 12:48 AM, Niklas Schnelle wrote: > On Wed, 2025-09-24 at 10:57 -0700, Farhan Ali wrote: >> On 8/26/2025 1:52 AM, Niklas Schnelle wrote: >>> Before disabling SR-IOV via config space accesses to the parent PF, >>> sriov_disable() first removes the PCI devices representing the VFs. >>> >>> Since commit 9d16947b7583 ("PCI: Add global pci_lock_rescan_remove()") >>> such removal operations are serialized against concurrent remove and >>> rescan using the pci_rescan_remove_lock. No such locking was ever added >>> in sriov_disable() however. In particular when commit 18f9e9d150fc >>> ("PCI/IOV: Factor out sriov_add_vfs()") factored out the PCI device >>> removal into sriov_del_vfs() there was still no locking around the >>> pci_iov_remove_virtfn() calls. >>> >>> On s390 the lack of serialization in sriov_disable() may cause double >>> remove and list corruption with the below (amended) trace being observed: >>> >>> PSW: 0704c00180000000 0000000c914e4b38 (klist_put+56) >>> GPRS: 000003800313fb48 0000000000000000 0000000100000001 0000000000000001 >>> 00000000f9b520a8 0000000000000000 0000000000002fbd 00000000f4cc9480 >>> 0000000000000001 0000000000000000 0000000000000000 0000000180692828 >>> 00000000818e8000 000003800313fe2c 000003800313fb20 000003800313fad8 >>> #0 [3800313fb20] device_del at c9158ad5c >>> #1 [3800313fb88] pci_remove_bus_device at c915105ba >>> #2 [3800313fbd0] pci_iov_remove_virtfn at c9152f198 >>> #3 [3800313fc28] zpci_iov_remove_virtfn at c90fb67c0 >>> #4 [3800313fc60] zpci_bus_remove_device at c90fb6104 >>> #5 [3800313fca0] __zpci_event_availability at c90fb3dca >>> #6 [3800313fd08] chsc_process_sei_nt0 at c918fe4a2 >>> #7 [3800313fd60] crw_collect_info at c91905822 >>> #8 [3800313fe10] kthread at c90feb390 >>> #9 [3800313fe68] __ret_from_fork at c90f6aa64 >>> #10 [3800313fe98] ret_from_fork at c9194f3f2. >>> >>> This is because in addition to sriov_disable() removing the VFs, the >>> platform also generates hot-unplug events for the VFs. This being >>> the reverse operation to the hotplug events generated by sriov_enable() >>> and handled via pdev->no_vf_scan. And while the event processing takes >>> pci_rescan_remove_lock and checks whether the struct pci_dev still >>> exists, the lack of synchronization makes this checking racy. >>> >>> Other races may also be possible of course though given that this lack >>> of locking persisted so long obversable races seem very rare. Even on >>> s390 the list corruption was only observed with certain devices since >>> the platform events are only triggered by the config accesses that come >>> after the removal, so as long as the removal finnished synchronously >>> they would not race. Either way the locking is missing so fix this by >>> adding it to the sriov_del_vfs() helper. >>> >>> Just lik PCI rescan-remove locking is also missing in sriov_add_vfs() >>> including for the error case where pci_stop_ad_remove_bus_device() is >>> called without the PCI rescan-remove lock being held. Even in the non >>> error case adding new PCI devices and busses should be serialized via >>> the PCI rescan-remove lock. Add the necessary locking. >>> >>> Cc: stable@vger.kernel.org >>> Fixes: 18f9e9d150fc ("PCI/IOV: Factor out sriov_add_vfs()") >>> Reviewed-by: Benjamin Block >>> Signed-off-by: Niklas Schnelle >>> --- >>> drivers/pci/iov.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c >>> index ac4375954c9479b5f4a0e666b5215094fdaeefc2..77dee43b785838d215b58db2d22088e9346e0583 100644 >>> --- a/drivers/pci/iov.c >>> +++ b/drivers/pci/iov.c >>> @@ -629,15 +629,18 @@ static int sriov_add_vfs(struct pci_dev *dev, u16 num_vfs) >>> if (dev->no_vf_scan) >>> return 0; >>> >>> + pci_lock_rescan_remove(); >>> for (i = 0; i < num_vfs; i++) { >>> rc = pci_iov_add_virtfn(dev, i); >> Should we move the lock/unlock to pci_iov_add_virtfn? As that's where >> the device is added to the bus? Similarly move the locking/unlocking to >> pci_iov_remove_virtfn? >> >> Thanks >> Farhan >> >> > I contemplated this as well. Most of the existing uses of > pci_lock/unlock_rescan_remove() are relatively coarse grained covering > e.g. the scanning of a whole bus. So I tried to keep this in line with > that such that all the VFs are added in a single critical section. > > Thanks, > Niklas Makes sense, the patch LGTM. Reviewed-by: Farhan Ali Thanks Farhan