On 19.04.21 09:01, Alistair Popple wrote:
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.
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
---
kernel/resource.c | 45 ++++++++++++++++++++++++++++++++++++++-------
1 file changed, 38 insertions(+), 7 deletions(-)
diff --git a/kernel/resource.c b/kernel/resource.c
index 75f8da722497..e8468e867495 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1801,25 +1801,56 @@ 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);
}
LGTM
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
