Re: [PATCH 3/4] ipc/sem.c: convert sem_array.sem_pending to struct list_head

Manfred Spraul
2008-06-07T14:53:16Z

Nadia Derbey wrote:
> Manfred Spraul wrote:
>> sem_array.sem_pending is a double linked list, the attached
>> patch converts it to struct list_head.
>>
>> Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
>
> Reviewed-By: Nadia Derbey <Nadia.Derbey@bull.net>
>
>>
>> @@ -438,16 +405,15 @@ static void update_queue (struct sem_array * sma)
>> int error;
>> struct sem_queue * q;
>>
>> - q = sma->sem_pending;
>> - while(q) {
>> + q = list_entry(sma->sem_pending.next, struct sem_queue, list);
>> + while(&q->list != &sma->sem_pending) {
>
> I guess here you are not using list_first_entry() because the pending
> requests might be empty?
>
Actually - no. I wasn't aware of list_first_entry().
But:
- Looking at list.h: list_first_entry() shouldn't be used on empty lists.
- the loop in update_queue() is complicated enough, some open-coding
doesn't hurt.

>> @@ -1194,7 +1171,6 @@ asmlinkage long sys_semtimedop(int semid,
>> struct sembuf __user *tsops,
>>
>> sma = sem_lock(ns, semid);
>> if (IS_ERR(sma)) {
>> - BUG_ON(queue.prev != NULL);
>
> Instead of removing it why not replacing the bug_ON() by a check on
> the queue still being linked?
>
The list_del() poisoning is IMHO efficient enough.

--
Manfred