acpi/nfit: Fix race accessing memdev in nfit_get_smbios_id()

Possible race accessing memdev structures after dropping the
mutex. Dan Williams says this could race against another thread
that is doing:

 # echo "ACPI0012:00" > /sys/bus/acpi/drivers/nfit/unbind

Reported-by: Jane Chu <jane.chu@oracle.com>
Fixes: 23222f8f8dce ("acpi, nfit: Add function to look up nvdimm...")
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 4ae953a..790691d 100644 (file)
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -714,6 +714,7 @@ int nfit_get_smbios_id(u32 device_handle, u16 *flags)
        struct acpi_nfit_memory_map *memdev;
        struct acpi_nfit_desc *acpi_desc;
        struct nfit_mem *nfit_mem;
+       u16 physical_id;
 
        mutex_lock(&acpi_desc_lock);
        list_for_each_entry(acpi_desc, &acpi_descs, list) {
@@ -721,10 +722,11 @@ int nfit_get_smbios_id(u32 device_handle, u16 *flags)
                list_for_each_entry(nfit_mem, &acpi_desc->dimms, list) {
                        memdev = __to_nfit_memdev(nfit_mem);
                        if (memdev->device_handle == device_handle) {
+                               *flags = memdev->flags;
+                               physical_id = memdev->physical_id;
                                mutex_unlock(&acpi_desc->init_mutex);
                                mutex_unlock(&acpi_desc_lock);
-                               *flags = memdev->flags;
-                               return memdev->physical_id;
+                               return physical_id;
                        }
                }
                mutex_unlock(&acpi_desc->init_mutex);