Messages in this thread |  | | | Subject | Re: [TOMOYO 05/15](repost) Domain transition handler functions. | | From | Tetsuo Handa <> | | Date | Tue, 2 Oct 2007 21:44:57 +0900 |
| |
Hello.
Thank you for your comment.
James Morris wrote: > Why do you need to avoid spinlocks for these manipulations?
I don't need to use spinlocks here. What I need to do here is avoid read/write reordering, so mb() will be appropriate here.
struct something { struct something *next; void *data; }; struct something *prev_ptr = ...; struct something *new_ptr = kmalloc(sizeof(*new_ptr), GFP_KERNEL); new_ptr->next = NULL; new_ptr->data = some_value; mb(); prev_ptr->next = new_ptr;
TOMOYO Linux doesn't use locks for reading singly-linked list. Thus, new_ptr->data has to be made visible to other CPUs before new_ptr is appended at the tail of singly-linked list. Otherwise, other CPU may read undefined new_ptr->data values.
Performance is not critical because this mb() is called only when appending new entry to the singly-linked list.
> Please use standard kernel list handling, per include/linux/list.h
Since new_ptr never be removed, new_ptr needn't to know it's previous element's address, thus having only ->next pointer is enough. new_ptr->next is assigned *only once* (initialized with NULL, and assigned non-NULL later), indicating "if ptr->next == NULL, ptr is the last element" and "if ptr->next != NULL, ptr is not the last element".
If I use "struct hlist_node" which has two pointers, it needs more memory than "struct something" which has one pointer. It is possible to use API defined in include/linux/list.h , but to reduce memory usage, I dare not use these API. Singly-linked list's rule in TOMOYO Linux is quite simple, "ptr->next is NULL if the last element" and "non-NULL if not".
Regards.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |