Re: [PATCH v3 05/11] iommu: Change group->devices to RCU-protected list

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Apr 23, 2026 at 08:08:59PM -0700, Nicolin Chen wrote:
> On Fri, Apr 24, 2026 at 10:53:49AM +0800, Baolu Lu wrote:
> > On 4/17/26 07:28, Nicolin Chen wrote:
> > 	    mutex_unlock(&group->mutex);
> >             /*
> >              * FIXME: Mis-locked because the ops->probe_finalize() call-back
> >              * of some IOMMU drivers calls arm_iommu_attach_device() which
> >              * in-turn might call back into IOMMU core code, where it tries
> >              * to take group->mutex, resulting in a deadlock.
> >              */
> >              for_each_group_device(group, gdev)
> >                         iommu_group_do_probe_finalize(gdev->dev);
> >         }
> > 
> >         return 0;
> > }
> > 
> > Will the change above trigger a lockdep splat due to this "mis-locked"
> > case?"
> 
> Oh, I missed this one. That's a good finding!
> 
> Perhaps we can just change it to list_for_each_entry_rcu holding
> rcu_read_lock() and drop the FIXME.

You can't hold rcu across that function IIRC

Jason