Commit a4e63bce authored Feb 27, 2020 by Jason Gunthorpe

RDMA/odp: Ensure the mm is still alive before creating an implicit child

Registration of a mmu_notifier requires the caller to hold a mmget() on
the mm as registration is not permitted to race with exit_mmap(). There is
a BUG_ON inside the mmu_notifier to guard against this.

Normally creating a umem is done against current which implicitly holds
the mmget(), however an implicit ODP child is created from a pagefault
work queue and is not guaranteed to have a mmget().

Call mmget() around this registration and abort faulting if the MM has
gone to exit_mmap().

Before the patch below the notifier was registered when the implicit ODP
parent was created, so there was no chance to register a notifier outside
of current.

Fixes: c571feca ("RDMA/odp: use mmu_notifier_get/put for 'struct ib_ucontext_per_mm'")
Link: https://lore.kernel.org/r/20200227114118.94736-1-leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

parent e38b55ea

drivers/infiniband/core/umem_odp.c

+19 −5

Original line number	Diff line number	Diff line
		@@ -181,15 +181,29 @@ ib_umem_odp_alloc_child(struct ib_umem_odp *root, unsigned long addr,
		odp_data->page_shift = PAGE_SHIFT;
		odp_data->notifier.ops = ops;

		/*
		* A mmget must be held when registering a notifier, the owming_mm only
		* has a mm_grab at this point.
		*/
		if (!mmget_not_zero(umem->owning_mm)) {
		ret = -EFAULT;
		goto out_free;
		}

		odp_data->tgid = get_pid(root->tgid);
		ret = ib_init_umem_odp(odp_data, ops);
		if (ret) {
		if (ret)
		goto out_tgid;
		mmput(umem->owning_mm);
		return odp_data;

		out_tgid:
		put_pid(odp_data->tgid);
		mmput(umem->owning_mm);
		out_free:
		kfree(odp_data);
		return ERR_PTR(ret);
		}
		return odp_data;
		}
		EXPORT_SYMBOL(ib_umem_odp_alloc_child);

		/**

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