Re: calling hooks from inside timer interrupt handler freezes machine

[Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx>]

Hi...

Comments are inlined...
> static int
> klife_open(struct inode* indode, struct file* filp)
> {
>     int ret;
>     struct klife *k;
>
>     ret = klife_alloc(&k);    
>     if (ret) 
>         return ret;
>   
OK, first you pass a pointer that lives inside kernel stack... Then..


> static int
> klife_alloc(struct klife **pk)
> {
>     int ret;
>     struct klife *k;
>
>     k = kmalloc(sizeof(*k), GFP_KERNEL);
>     if (!k) 
>         return -ENOMEM;                
>     memset(k, 0, sizeof(*k));        
>
>     ret = init_klife(k);
>     if (ret) 
>         kfree(k);
>
>     *pk = k;
>     
>     return ret;
> }
>   
You assign memory block to this pointer. Then you get back to 
klife_open(). This function itself eventually exits and the kernel stack 
size is reduced (but not gone at the moment, esp register is just 
increased IIRC).

Up until nothing mess with kernel stack, your hook will be just fine. 
But as soon as something use kernel stack, it will overwrite your 
klife_struct *k pointer so it no longer points to correct memory 
address...and boom.

Solution: make that pointer static or put it outside function scope. 
That way, it won't reside on kernel stack.

regards,

Mulyadi


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