Question

Hi i’m programming kernel (2.6) for the first time and i have a problem using spinlocks.

I’m trying to add this system call (inserisci_nodo) that externalizes a structure (an ibrid list-hashtable) and try to add a node (Persona) in this structure, if the node already exists it will be updated.

I have a problem on the first “update”, in fact, if I try to insert all new nodes it works! But if I try to insert an already existent node this seems already locked. I cannot understand why.

This is the code.

 asmlinkage long sys_inserisci_nodo(key_t id, char* nome, int eta){
    persona *p;
    spin_lock(&htable.lock);
    printk("<3> PRESO SPIN_LOCK TABELLA\n");

    if((p=lookup(id))!=NULL){   //Update an already existent node
        printk("<3> NODO %d, AGGIORNAMENTO IN CORSO....\n",id);    <--- system locked.
        spin_lock(&(p->lock));
        printk("<3> PRESO SPIN_LOCK NODO %d\n",id);

        p->eta=eta;
        strcpy(p->nome, nome);
        printk("<3> NODO %d, AGGIORNAMENTO... OK\n",id);

        spin_unlock(&p->lock);

        printk("<3> RILASCIATO SPIN_LOCK NODO %d\n",id);
        spin_unlock(&htable.lock);
        printk("<3> RILASCIATO SPIN_LOCK TABELLA\n");

        return p->id;
    }
    else{       //Insert new node.
        p = (persona *) kmalloc(sizeof(persona),GFP_KERNEL);
        if(p==NULL){
            printk("<3> ERRORE NELL'ALLOCARE MEMORIA PER PERSONA CON ID: %d\n",id);
            spin_unlock(&htable.lock);
            printk("<3> RILASCIATO SPIN_LOCK TABELLA\n");
            return -1;
        }
        p->id = id;
        p->eta=eta;
        p->nome = (char*) kmalloc(sizeof(nome),GFP_KERNEL);
        strcpy(p->nome, nome);
        printk("<3> NODO %d, AGGIUNTO\n",id);

        int h = hashfunc(id);
        p->next=htable.persone[h];
        htable.persone[h] = p;
        spin_unlock(&htable.lock);
        printk("<3> RILASCIATO SPIN_LOCK TABELLA\n");
        return h;   

    }
}

Sorry for the italian language on the code, I add some english comments on the code.

These are the two structures (hashtable and “persona” (node)).

typedef struct _persona{
    key_t id;
    char *nome;
    int eta;
    spinlock_t lock;
    struct _persona *next;
}persona;

typedef struct _hashtable{
    spinlock_t lock;
    int occupati;
    persona* persone[MAX_NUM];
}hashtable;

“lookup(key)” and “hash(key)” are two simple functions to get nodes from the struct.

I hope you have an idea about it 🙂

bye!

Answer 1

You need to initialize the spinlock:

p->id = id;
p->eta=eta;
p->nome = (char*) kmalloc(sizeof(nome),GFP_KERNEL);
spin_lock_init(&p->lock); // <- don't forget to initialize the locks!