pradeep singh wrote:
On 3/22/06, Bennett, Robert P <Robert.Bennett@xxxxxx> wrote:
-----Original Message-----
From: kernelnewbies-bounce@xxxxxxxxxxxx
[mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of pradeep singh
Sent: Wednesday, March 22, 2006 9:59 AM
To: kernel-issues
Subject: spinlocks and kernel timer !!!
Hi
static void some_method()
{
unsigned long expires;
static struct timer_list *timer;
expires = jiffes + 20;
data = 5;
timer->expires = expires;
timer->function = my_function;
timer->data = data;
init_timer(timer); /*initalise timer*/
spin_lock_irqsave(&spinlock, iflags);
spin_unlock_irqrestore(&spinlock, iflags);
return 0;
}
static int __init mod_init( void )
{
printk(KERN_DEBUG "in init..\n");
some_method();
printk(KERN_DEBUG "after some method in init..\n");
return 0;
};
static void __exit mod_exit( void )
{
printk(KERN_DEBUG "bye world...\n");
}
My question is between spin_lock_irqsave() and
spin_unlock_irqrestore() code is supposed to be atomic right?
Now as i have initialised a timer structure in the
function.If the jiffies gets equal to expires in between
spinlock() and spinunlock() will my_function() execute?
What will happen and why?
You will OOPS as soon as you dereference "timer", since you did
not initialize it.
does this means init_timer( timer ) will not initialise the timer ?
I think LDD3 says about init_timer(timer) to initialise the timer :),
where am i getting this all wrong ? Can you please explain ?
thank you
As for the behavior of the timer, I would expect that nothing is
going to happen until after the
spin_unlock_irqrestore() has been executed, since local
interrupts are disabled.
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Initializing is one thing and allocating memory for a pointer is
another. You will need to allocate memory for the timer before you
access the fields. If you see the kernel code, init_timer sets the list
head and base fields of the structure.
Sanjay
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