Commit 56fd9491 authored May 06, 2021 by Alistair Popple Committed by Linus Torvalds May 07, 2021

kernel/resource: fix locking in request_free_mem_region

request_free_mem_region() is used to find an empty range of physical
addresses for hotplugging ZONE_DEVICE memory.  It does this by iterating
over the range of possible addresses using region_intersects() to see if
the range is free before calling request_mem_region() to allocate the
region.

However the resource_lock is dropped between these two calls meaning by
the time request_mem_region() is called in request_free_mem_region()
another thread may have already reserved the requested region.  This
results in unexpected failures and a message in the kernel log from
hitting this condition:

        /*
         * mm/hmm.c reserves physical addresses which then
         * become unavailable to other users.  Conflicts are
         * not expected.  Warn to aid debugging if encountered.
         */
        if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
                pr_warn("Unaddressable device %s %pR conflicts with %pR",
                        conflict->name, conflict, res);

These unexpected failures can be corrected by holding resource_lock across
the two calls.  This also requires memory allocation to be performed prior
to taking the lock.

Link: https://lkml.kernel.org/r/20210419070109.4780-3-apopple@nvidia.com


Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Muchun Song <smuchun@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 63cdafe0

kernel/resource.c

+38 −7

Original line number	Diff line number	Diff line
		@@ -1780,25 +1780,56 @@ static struct resource __request_free_mem_region(struct device dev,
		{
		resource_size_t end, addr;
		struct resource *res;
		struct region_devres *dr = NULL;

		size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
		end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) - 1);
		addr = end - size + 1UL;

		res = alloc_resource(GFP_KERNEL);
		if (!res)
		return ERR_PTR(-ENOMEM);

		if (dev) {
		dr = devres_alloc(devm_region_release,
		sizeof(struct region_devres), GFP_KERNEL);
		if (!dr) {
		free_resource(res);
		return ERR_PTR(-ENOMEM);
		}
		}

		write_lock(&resource_lock);
		for (; addr > size && addr >= base->start; addr -= size) {
		if (region_intersects(addr, size, 0, IORES_DESC_NONE) !=
		if (__region_intersects(addr, size, 0, IORES_DESC_NONE) !=
		REGION_DISJOINT)
		continue;

		if (dev)
		res = devm_request_mem_region(dev, addr, size, name);
		else
		res = request_mem_region(addr, size, name);
		if (!res)
		return ERR_PTR(-ENOMEM);
		if (!__request_region_locked(res, &iomem_resource, addr, size,
		name, 0))
		break;

		if (dev) {
		dr->parent = &iomem_resource;
		dr->start = addr;
		dr->n = size;
		devres_add(dev, dr);
		}

		res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
		write_unlock(&resource_lock);

		/*
		* A driver is claiming this region so revoke any mappings.
		*/
		revoke_iomem(res);
		return res;
		}
		write_unlock(&resource_lock);

		free_resource(res);
		if (dr)
		devres_free(dr);

		return ERR_PTR(-ERANGE);
		}