[PATCH v2] kernel/resource: Fix locking in request_free_mem_region

Alistair Popple
2021-03-26T01:20:50Z

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.

region_intersects() obtains a read lock before walking the resource tree
to protect against concurrent changes. However it drops the lock prior
to returning. This means by the time request_mem_region() is called in
request_free_mem_region() another thread may have already reserved the
requested region resulting 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);

To fix this create versions of region_intersects() and
request_mem_region() that allow the caller to take the appropriate lock
such that it may be held over the required calls.

Instead of creating another version of devm_request_mem_region() that
doesn't take the lock open-code it to allow the caller to pre-allocate
the required memory prior to taking the lock.

Fixes: 0c385190392d8 ("resource: add a not device managed request_free_mem_region variant")
Fixes: 0092908d16c60 ("mm: factor out a devm_request_free_mem_region helper")
Fixes: 4ef589dc9b10c ("mm/hmm/devmem: device memory hotplug using ZONE_DEVICE")
Signed-off-by: Alistair Popple <apopple@nvidia.com>

---

v2:
- Added Fixes tag

---
kernel/resource.c | 146 +++++++++++++++++++++++++++++-----------------
1 file changed, 94 insertions(+), 52 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 627e61b0c124..2d4652383dd2 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -523,6 +523,34 @@ int __weak page_is_ram(unsigned long pfn)
}
EXPORT_SYMBOL_GPL(page_is_ram);

+static int __region_intersects(resource_size_t start, size_t size,
+ unsigned long flags, unsigned long desc)
+{
+ struct resource res;
+ int type = 0; int other = 0;
+ struct resource *p;
+
+ res.start = start;
+ res.end = start + size - 1;
+
+ for (p = iomem_resource.child; p ; p = p->sibling) {
+ bool is_type = (((p->flags & flags) == flags) &&
+ ((desc == IORES_DESC_NONE) ||
+ (desc == p->desc)));
+
+ if (resource_overlaps(p, &res))
+ is_type ? type++ : other++;
+ }
+
+ if (type == 0)
+ return REGION_DISJOINT;
+
+ if (other == 0)
+ return REGION_INTERSECTS;
+
+ return REGION_MIXED;
+}
+
/**
* region_intersects() - determine intersection of region with known resources
* @start: region start address
@@ -546,31 +574,12 @@ EXPORT_SYMBOL_GPL(page_is_ram);
int region_intersects(resource_size_t start, size_t size, unsigned long flags,
unsigned long desc)
{
- struct resource res;
- int type = 0; int other = 0;
- struct resource *p;
-
- res.start = start;
- res.end = start + size - 1;
+ int rc;

read_lock(&resource_lock);
- for (p = iomem_resource.child; p ; p = p->sibling) {
- bool is_type = (((p->flags & flags) == flags) &&
- ((desc == IORES_DESC_NONE) ||
- (desc == p->desc)));
-
- if (resource_overlaps(p, &res))
- is_type ? type++ : other++;
- }
+ rc = __region_intersects(start, size, flags, desc);
read_unlock(&resource_lock);
-
- if (type == 0)
- return REGION_DISJOINT;
-
- if (other == 0)
- return REGION_INTERSECTS;
-
- return REGION_MIXED;
+ return rc;
}
EXPORT_SYMBOL_GPL(region_intersects);

@@ -1171,31 +1180,17 @@ struct address_space *iomem_get_mapping(void)
return smp_load_acquire(&iomem_inode)->i_mapping;
}

-/**
- * __request_region - create a new busy resource region
- * @parent: parent resource descriptor
- * @start: resource start address
- * @n: resource region size
- * @name: reserving caller's ID string
- * @flags: IO resource flags
- */
-struct resource * __request_region(struct resource *parent,
- resource_size_t start, resource_size_t n,
- const char *name, int flags)
+static bool request_region_locked(struct resource *parent,
+ struct resource *res, resource_size_t start,
+ resource_size_t n, const char *name, int flags)
{
- DECLARE_WAITQUEUE(wait, current);
- struct resource *res = alloc_resource(GFP_KERNEL);
struct resource *orig_parent = parent;
-
- if (!res)
- return NULL;
+ DECLARE_WAITQUEUE(wait, current);

res->name = name;
res->start = start;
res->end = start + n - 1;

- write_lock(&resource_lock);
-
for (;;) {
struct resource *conflict;

@@ -1230,16 +1225,39 @@ struct resource * __request_region(struct resource *parent,
write_lock(&resource_lock);
continue;
}
- /* Uhhuh, that didn't work out.. */
- free_resource(res);
- res = NULL;
- break;
+ return false;
}
- write_unlock(&resource_lock);

if (res && orig_parent == &iomem_resource)
revoke_iomem(res);

+ return true;
+}
+
+/**
+ * __request_region - create a new busy resource region
+ * @parent: parent resource descriptor
+ * @start: resource start address
+ * @n: resource region size
+ * @name: reserving caller's ID string
+ * @flags: IO resource flags
+ */
+struct resource *__request_region(struct resource *parent,
+ resource_size_t start, resource_size_t n,
+ const char *name, int flags)
+{
+ struct resource *res = alloc_resource(GFP_KERNEL);
+
+ if (!res)
+ return NULL;
+
+ write_lock(&resource_lock);
+ if (!request_region_locked(parent, res, start, n, name, flags)) {
+ /* Uhhuh, that didn't work out.. */
+ free_resource(res);
+ res = NULL;
+ }
+ write_unlock(&resource_lock);
return res;
}
EXPORT_SYMBOL(__request_region);
@@ -1779,26 +1797,50 @@ static struct resource *__request_free_mem_region(struct device *dev,
{
resource_size_t end, addr;
struct resource *res;
+ struct region_devres *dr = NULL;
+
+ 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);
+ }
+ }

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

+ 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(&iomem_resource, res, addr,
+ size, name, 0))
+ break;
+
res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
+ if (dev) {
+ dr->parent = &iomem_resource;
+ dr->start = addr;
+ dr->n = size;
+ devres_add(dev, dr);
+ }
+
+ write_unlock(&resource_lock);
return res;
}

+ write_unlock(&resource_lock);
+ free_resource(res);
+
return ERR_PTR(-ERANGE);
}

--
2.20.1