Re: [PATCH v3 02/14] thermal: core: Rearrange checks in thermal_bind_cdev_to_trip()

From: lihuisong (C)
Date: Wed Aug 21 2024 - 07:45:44 EST



在 2024/8/21 18:49, Daniel Lezcano 写道:
On 21/08/2024 11:44, lihuisong (C) wrote:

在 2024/8/21 17:28, Daniel Lezcano 写道:
On 21/08/2024 10:49, lihuisong (C) wrote:

[ ... ]

-    list_for_each_entry(pos2, &thermal_cdev_list, node) {
-        if (pos2 == cdev)
-            break;
-    }
+    lockdep_assert_held(&thermal_list_lock);
-    if (tz != pos1 || cdev != pos2)
+    if (list_empty(&tz->node) || list_empty(&cdev->node))
The old verification is ensure that tz and cdev already add to thermal_tz_list and thermal_cdev_list,respectively.
Namely, tz and cdev are definitely registered and intialized.
The check is ok for all untizalized thermal_zone_device and cooling device.
But the new verification doesn't seem to do that.

If the tz or the cdev are registered then their "->node" is not empty because they are linked with the thermal_list and cdev_list

So either way is browsing the lists to find the tz/cdev or just check "->node" is not empty. The latter the faster.
Assume that tz/cdev isn't intiazlized and registered to thermal_tz_list or thermal_cdev_list. And then directly call this interface.

Then there is a bug in the internal code because the thermal_zone_device_register*() and cooling_device_device_register() allocate and initialize those structures.

The caller of the function is supposed to use the API provided by the thermal framework. It is not possible to plan every stupid things a driver can do. In this particular case, very likely the kernel will crash immediately which is a sufficient test for me and coercive enough to have the API user to put its code in question ;)

A good point. Agree.