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Thu, 25 Sep 2025 07:48:07 +0000 (GMT) Message-ID: <9fb43fc399ac5917605b7bc721c4b0affb8ca255.camel@linux.ibm.com> Subject: Re: [PATCH 1/2] PCI/IOV: Add missing PCI rescan-remove locking when enabling/disabling SR-IOV From: Niklas Schnelle To: Farhan Ali , 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 Date: Thu, 25 Sep 2025 09:48:07 +0200 In-Reply-To: References: <20250826-pci_fix_sriov_disable-v1-0-2d0bc938f2a3@linux.ibm.com> <20250826-pci_fix_sriov_disable-v1-1-2d0bc938f2a3@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 3/1pjpNlSaX/qg3ZM8+/EiSGc7uEPklLYu3gRGxcWV/944HdUyLcnjrZwCn2+gg9ncVJjsimS0ro/ 2wU2RPE4ju6NMBn5Go26sAj1owdYQQv9t0d71CmZS9Bh+2+cLjC7HvyTHKFxVGOznUL+j1a45VrVS XQ+nhTVjvgvXR84z10bOvLiwxJZ/00pwNi7uCdSYnZFLQ4S/JGMs4lhOiCGJhJ/9FR7JVw/1t1G9a UlqVp23AXwzbcoV2fxyE/CsVpHcyOWGDahGLcH7QeitN6cjltf9ymw2spBzpRnfFn80nVxgSYVG1d w75ksBAuQ/3e+oTQk4GAa2ShoNVsvR9GYn7rnsDN5pVILDhdPO3J2PGIXa5ipQnvwb3EHvPXyzakY tK50fBUPKk3XnkRwRYEbbPEB7YT+ccF/HioCryqDPWUivXF8qf6Jw5T1mhwukUV1i+QyJzJxGPh19 /N2/GK7/yS5wrt0Lwxzevc5g+jX8RyjzywOZGHTVu9KIQiG8Pqx33UxZvykjaqTMjo7kaAdGEkrHZ dVHqoPZwhCsgQARAQABtChOaWtsYXMgU2NobmVsbGUgPHNjaG5lbGxlQGxpbnV4LmlibS5jb20+iQ JXBBMBCABBAhsBBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAhkBFiEEnbAAstJ1IDCl9y3cr+Q/Fej CYJAFAmesutgFCQenEYkACgkQr+Q/FejCYJDIzA//W5h3t+anRaztihE8ID1c6ifS7lNUtXr0wEKx Qm6EpDQKqFNP+n3R4A5w4gFqKv2JpYQ6UJAAlaXIRTeT/9XdqxQlHlA20QWI7yrJmoYaF74ZI9s/C 8aAxEzQZ64NjHrmrZ/N9q8JCTlyhk5ZEV1Py12I2UH7moLFgBFZsPlPWAjK2NO/ns5UJREAJ04pR9 XQFSBm55gsqkPp028cdoFUD+IajGtW7jMIsx/AZfYMZAd30LfmSIpaPAi9EzgxWz5habO1ZM2++9e W6tSJ7KHO0ZkWkwLKicrqpPvA928eNPxYtjkLB2XipdVltw5ydH9SLq0Oftsc4+wDR8TqhmaUi8qD Fa2I/0NGwIF8hjwSZXtgJQqOTdQA5/6voIPheQIi0NBfUr0MwboUIVZp7Nm3w0QF9SSyTISrYJH6X qLp17NwnGQ9KJSlDYCMCBJ+JGVmlcMqzosnLli6JszAcRmZ1+sd/f/k47Fxy1i6o14z9Aexhq/UgI 5InZ4NUYhf5pWflV41KNupkS281NhBEpChoukw25iZk0AsrukpJ74x69MJQQO+/7PpMXFkt0Pexds XQrtsXYxLDQk8mgjlgsvWl0xlk7k7rddN1+O/alcv0yBOdvlruirtnxDhbjBqYNl8PCbfVwJZnyQ4 SAX2S9XiGeNtWfZ5s2qGReyAcd2nBna0KU5pa2xhcyBTY2huZWxsZSA8bmlrbGFzLnNjaG5lbGxlQ GlibS5jb20+iQJUBBMBCAA+AhsBBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAFiEEnbAAstJ1IDCl9y 3cr+Q/FejCYJAFAmesuuEFCQenEYkACgkQr+Q/FejCYJCosA/9GCtbN8lLQkW71n/CHR58BAA5ct1 KRYiZNPnNNAiAzjvSb0ezuRVt9H0bk/tnj6pPj0zdyU2bUj9Ok3lgocWhsF2WieWbG4dox5/L1K28 qRf3p+vdPfu7fKkA1yLE5GXffYG3OJnqR7OZmxTnoutj81u/tXO95JBuCSJn5oc5xMQvUUFzLQSbh prIWxcnzQa8AHJ+7nAbSiIft/+64EyEhFqncksmzI5jiJ5edABiriV7bcNkK2d8KviUPWKQzVlQ3p LjRJcJJHUAFzsZlrsgsXyZLztAM7HpIA44yo+AVVmcOlmgPMUy+A9n+0GTAf9W3y36JYjTS+ZcfHU KP+y1TRGRzPrFgDKWXtsl1N7sR4tRXrEuNhbsCJJMvcFgHsfni/f4pilabXO1c5Pf8fiXndCz04V8 ngKuz0aG4EdLQGwZ2MFnZdyf3QbG3vjvx7XDlrdzH0wUgExhd2fHQ2EegnNS4gNHjq82uLPU0hfcr obuI1D74nV0BPDtr7PKd2ryb3JgjUHKRKwok6IvlF2ZHMMXDxYoEvWlDpM1Y7g81NcKoY0BQ3ClXi a7vCaqAAuyD0zeFVGcWkfvxYKGqpj8qaI/mA8G5iRMTWUUUROy7rKJp/y2ioINrCul4NUJUujfx4k 7wFU11/YNAzRhQG4MwoO5e+VY66XnAd+XPyBIlvy0K05pa2xhcyBTY2huZWxsZSA8bmlrbGFzLnNj aG5lbGxlQGdtYWlsLmNvbT6JAlQEEwEIAD4CGwEFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AWIQSds ACy0nUgMKX3Ldyv5D8V6MJgkAUCZ6y64QUJB6cRiQAKCRCv5D8V6MJgkEr/D/9iaYSYYwlmTJELv+ +EjsIxXtneKYpjXEgNnPwpKEXNIpuU/9dcVDcJ10MfvWBPi3sFbIzO9ETIRyZSgrjQxCGSIhlbom4 D8jVzTA698tl9id0FJKAi6T0AnBF7CxyqofPUzAEMSj9ynEJI/Qu8pHWkVp97FdJcbsho6HNMthBl +Qgj9l7/Gm1UW3ZPvGYgU75uB/mkaYtEv0vYrSZ+7fC2Sr/O5SM2SrNk+uInnkMBahVzCHcoAI+6O Enbag+hHIeFbqVuUJquziiB/J4Z2yT/3Ps/xrWAvDvDgdAEr7Kn697LLMRWBhGbdsxdHZ4ReAhc8M 8DOcSWX7UwjzUYq7pFFil1KPhIkHctpHj2Wvdnt+u1F9fN4e3C6lckUGfTVd7faZ2uDoCCkJAgpWR 10V1Q1Cgl09VVaoi6LcGFPnLZfmPrGYiDhM4gyDDQJvTmkB+eMEH8u8V1X30nCFP2dVvOpevmV5Uk onTsTwIuiAkoTNW4+lRCFfJskuTOQqz1F8xVae8KaLrUt2524anQ9x0fauJkl3XdsVcNt2wYTAQ/V nKUNgSuQozzfXLf+cOEbV+FBso/1qtXNdmAuHe76ptwjEfBhfg8L+9gMUthoCR94V0y2+GEzR5nlD 5kfu8ivV/gZvij+Xq3KijIxnOF6pd0QzliKadaFNgGw4FoUeZo0rQhTmlrbGFzIFNjaG5lbGxlIDx uaWtzQGtlcm5lbC5vcmc+iQJUBBMBCAA+AhsBBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAFiEEnbAA stJ1IDCl9y3cr+Q/FejCYJAFAmesuuEFCQenEYkACgkQr+Q/FejCYJC6yxAAiQQ5NAbWYKpkxxjP/ AajXheMUW8EtK7EMJEKxyemj40laEs0wz9owu8ZDfQl4SPqjjtcRzUW6vE6JvfEiyCLd8gUFXIDMS l2hzuNot3sEMlER9kyVIvemtV9r8Sw1NHvvCjxOMReBmrtg9ooeboFL6rUqbXHW+yb4GK+1z7dy+Q 9DMlkOmwHFDzqvsP7eGJN0xD8MGJmf0L5LkR9LBc+jR78L+2ZpKA6P4jL53rL8zO2mtNQkoUO+4J6 0YTknHtZrqX3SitKEmXE2Is0Efz8JaDRW41M43cE9b+VJnNXYCKFzjiqt/rnqrhLIYuoWCNzSJ49W vt4hxfqh/v2OUcQCIzuzcvHvASmt049ZyGmLvEz/+7vF/Y2080nOuzE2lcxXF1Qr0gAuI+wGoN4gG lSQz9pBrxISX9jQyt3ztXHmH7EHr1B5oPus3l/zkc2Ajf5bQ0SE7XMlo7Pl0Xa1mi6BX6I98CuvPK SA1sQPmo+1dQYCWmdQ+OIovHP9Nx8NP1RB2eELP5MoEW9eBXoiVQTsS6g6OD3rH7xIRxRmuu42Z5e 0EtzF51BjzRPWrKSq/mXIbl5nVW/wD+nJ7U7elW9BoJQVky03G0DhEF6fMJs08DGG3XoKw/CpGtMe 2V1z/FRotP5Fkf5VD3IQGtkxSnO/awtxjlhytigylgrZ4wDpSE= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=J5Cq7BnS c=1 sm=1 tr=0 ts=68d4f3bc cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=tmWI2QDjmt9rcYb-4t0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: o89TCv57fsfiIcqbj50abCdBm-KM_9T3 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTIwMDAxNSBTYWx0ZWRfXzjxFyCHKbiNV fMCYfc4BsunVq3fHcFocs82BrutgGkkPd3r61vFpF0TCOU8Kr7LBdbatZFF7OVXJXyhDHJSZzgQ K2riwqDkpvt+CvVniwXs4xk1arSGy8aZk6VqsLg+4wQmf/2AAxeSNxZntWU7rV0mOk5WAi4+fiu Uwqs+WyiJjd+HZ13YRizl1IY3Geog3Iue8IEDRzMGbh7THU80Tfd7sBb6NrTptgBbzZ4FyBn2oI UEJmU3L/G8ylgTCoLZ1WFiXUaG9vkQLm8YMrkjTkn76kx2niXE6n9F8q9COyEgDfKbDUHgM6i23 MxqVMuqwMtNLe55ETr9PYfYHbBNUd8MulskWorfhqOF69kRkIAM56k5bAu3rG9K+yluroHeW64i PLpeC8W6 X-Proofpoint-ORIG-GUID: o89TCv57fsfiIcqbj50abCdBm-KM_9T3 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=2025-09-24_07,2025-09-24_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 malwarescore=0 spamscore=0 bulkscore=0 phishscore=0 clxscore=1015 adultscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509200015 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. > >=20 > > 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. > >=20 > > On s390 the lack of serialization in sriov_disable() may cause double > > remove and list corruption with the below (amended) trace being observe= d: > >=20 > > PSW: 0704c00180000000 0000000c914e4b38 (klist_put+56) > > GPRS: 000003800313fb48 0000000000000000 0000000100000001 000000000000= 0001 > > 00000000f9b520a8 0000000000000000 0000000000002fbd 00000000f4cc= 9480 > > 0000000000000001 0000000000000000 0000000000000000 000000018069= 2828 > > 00000000818e8000 000003800313fe2c 000003800313fb20 000003800313= fad8 > > #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. > >=20 > > 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. > >=20 > > 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. > >=20 > > 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. > >=20 > > 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(+) > >=20 > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c > > index ac4375954c9479b5f4a0e666b5215094fdaeefc2..77dee43b785838d215b58db= 2d22088e9346e0583 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; > > =20 > > + pci_lock_rescan_remove(); > > for (i =3D 0; i < num_vfs; i++) { > > rc =3D pci_iov_add_virtfn(dev, i); >=20 > Should we move the lock/unlock to pci_iov_add_virtfn? As that's where=20 > the device is added to the bus? Similarly move the locking/unlocking to= =20 > pci_iov_remove_virtfn? >=20 > Thanks > Farhan >=20 >=20 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