Messages in this thread | | | Date | Wed, 1 May 2019 09:38:03 +1000 | From | "Tobin C. Harding" <> | Subject | kobject_init_and_add() confusion |
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Hi,
Looks like I've created a bit of confusion trying to fix memleaks in calls to kobject_init_and_add(). Its spread over various patches and mailing lists so I'm starting a new thread and CC'ing anyone that commented on one of those patches.
If there is a better way to go about this discussion please do tell me.
The problem -----------
Calls to kobject_init_and_add() are leaking memory throughout the kernel because of how the error paths are handled.
The solution ------------
Write the error path code correctly.
Example -------
We have samples/kobject/kobject-example.c but it uses kobject_create_and_add(). I thought of adding another example file here but could not think of how to do it off the top of my head without being super contrived. Can add this to the TODO list if it will help.
Here is an attempted canonical usage of kobject_init_and_add() typical of the code that currently is getting it wrong. This is the second time I've written this and the first time it was wrong even after review (you know who you are, you are definitely buying the next round of drinks :)
Assumes we have an object in memory already that has the kobject embedded in it. Variable 'kobj' below would typically be &ptr->kobj
void fn(void) { int ret;
ret = kobject_init_and_add(kobj, ktype, NULL, "foo"); if (ret) { /* * This means kobject_init() has succeeded * but kobject_add() failed. */ goto err_put; }
ret = some_init_fn(); if (ret) { /* * We need to wind back kobject_add() AND kobject_put(). * kobject_add() incremented the refcount in * kobj->parent, that needs to be decremented THEN we need * the call to kobject_put() to decrement the refcount of kobj. */ goto err_del; }
ret = some_other_init_fn(); if (ret) goto other_err;
kobject_uevent(kobj, KOBJ_ADD); return 0;
other_err: other_clean_up_fn(); err_del: kobject_del(kobj); err_put: kobject_put(kobj);
return ret; }
Have I got this correct?
TODO ----
- Fix all the callsites to kobject_init_and_add() - Further clarify the function docstring for kobject_init_and_add() [perhaps] - Add a section to Documentation/kobject.txt [optional] - Add a sample usage file under samples/kobject [optional]
Thanks, Tobin.
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