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<7cf012ca23e9ac9fb648adc9467edc54f1e3f6cd.camel@linux.ibm.com> Subject: Re: [PATCH v2 6/7] s390/pci: Set MSI_FLAG_NO_AFFINITY at IRQ init time From: Niklas Schnelle To: Tobias Schumacher , Gerd Bayer , Julian Ruess , Farhan Ali , Christian Borntraeger , Halil Pasic , Matthew Rosato Cc: Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20261005-s390_irq_domain_fixes-v2-6-d45b824874c0@linux.ibm.com> References: <20261005-s390_irq_domain_fixes-v2-0-d45b824874c0@linux.ibm.com> <20261005-s390_irq_domain_fixes-v2-6-d45b824874c0@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/ 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priorityscore=1501 spamscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 malwarescore=0 clxscore=1015 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2610060060 On Mon, 2026-10-05 at 14:03 +0200, Tobias Schumacher wrote: > MSI_FLAG_NO_AFFINITY is added to zpci_msi_parent_ops.required_flags from > zpci_create_parent_msi_domain(), which runs for every new PCI bus, > including buses created at runtime from a hotplug availability event. >=20 > That is a non-atomic read-modify-write on a field which > msi_lib_init_dev_msi_info() reads without a common lock while setting up > MSI for a device on an already existing bus: >=20 > required_flags =3D pops->required_flags; >=20 > The stored value is always the same, so no caller observes a change, but > the race need not exist: irq_delivery is decided once in zpci_irq_init() > and never changes afterwards. >=20 > Set the flag there instead, before any parent domain exists. >=20 > Signed-off-by: Tobias Schumacher > --- > arch/s390/pci/pci_irq.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) >=20 > diff --git a/arch/s390/pci/pci_irq.c b/arch/s390/pci/pci_irq.c > index 682bceb6525e..661867a1ffad 100644 > --- a/arch/s390/pci/pci_irq.c > +++ b/arch/s390/pci/pci_irq.c > @@ -523,9 +523,6 @@ int zpci_create_parent_msi_domain(struct zpci_bus *zb= us) > return -ENOMEM; > } > =20 > - if (irq_delivery =3D=3D FLOATING) > - zpci_msi_parent_ops.required_flags |=3D MSI_FLAG_NO_AFFINITY; > - > zbus->msi_parent_domain =3D msi_create_parent_irq_domain(&info, &zpci_m= si_parent_ops); > if (!zbus->msi_parent_domain) { > irq_domain_free_fwnode(info.fwnode); > @@ -636,6 +633,9 @@ int __init zpci_irq_init(void) > if (s390_pci_force_floating) > irq_delivery =3D FLOATING; > =20 > + if (irq_delivery =3D=3D FLOATING) > + zpci_msi_parent_ops.required_flags |=3D MSI_FLAG_NO_AFFINITY; > + > if (irq_delivery =3D=3D DIRECTED) > zpci_airq.handler =3D zpci_directed_irq_handler; > =20 Looks good to me and I agree the race is benign as everyone races to write the same value but this is certainly cleaner. Thanks. Reviewed-by: Niklas Schnelle