Hi Abhinav, On Sat, Jun 16, 2018 at 11:52 PM, Abhinav Misra <abhitheextremeeng@gmail.com> wrote:

Hi Guys,

I am Abhinav, new to this mailing list.

Have some query on tasklet. Going Jerry Cooperstein's LDD book chapter-20 (Interrupt handling and deferrable functions) lab exercises.

Attached is the snapshot of problem-2,3. I am referring here to only tasklet.

Solution to problem for tasklet provided is below.

-------------------------------------------------------------------------------------------- static void t_fun(unsigned long t_arg) { struct my_dat *data = (struct my_dat *)t_arg; atomic_inc(&counter_bh); pr_info( "In BH: counter_th = %d, counter_bh = %d, jiffies=%ld, %ld\n", atomic_read(&counter_th), atomic_read(&counter_bh), data->jiffies, jiffies); }

static DECLARE_TASKLET(t_name, t_fun, (unsigned long)&my_data);

/* initialize tasklet */ static irqreturn_t my_interrupt(int irq, void *dev_id) { struct my_dat *data = (struct my_dat *)dev_id; atomic_inc(&counter_th); data->jiffies = jiffies; tasklet_schedule(&t_name); mdelay(delay); /* hoke up a delay to try to cause pileup */ return IRQ_NONE; /* we return IRQ_NONE because we are just observing */ }

This is general one where the tasklet is initialized either in Init or probe. There is only one tasklet created here which is scheduled on IRQ.

module_init(my_generic_init); module_exit(my_generic_exit);

-------------------------------------------------------------------------------------------------

Above solution will miss some bottom halves. To solve this problem, a solution is provided using dynamically allocated tasklet as below

------------------------------------------------------------------------- static void t_fun(unsigned long t_arg) { struct my_dat *data = (struct my_dat *)t_arg; atomic_inc(&counter_bh); pr_info("In BH: counter_th = %d, counter_bh = %d, jiffies=%ld, %ld\n", atomic_read(&counter_th), atomic_read(&counter_bh), data->jiffies, jiffies); kfree(data); }

static irqreturn_t my_interrupt(int irq, void *dev_id) { struct tasklet_struct *t; struct my_dat *data;

data = (struct my_dat *)kmalloc(sizeof(struct my_dat), GFP_ATOMIC); t = &data->tsk; data->jiffies = jiffies;

tasklet_init(t, t_fun, (unsigned long)data);

atomic_inc(&counter_th); tasklet_schedule(t); mdelay(delay); /* hoke up a delay to try to cause pileup */ return IRQ_NONE; /* we return IRQ_NONE because we are just observing */ }

This part of code initializes a new tasklet everytime on the IRQ. Hence each time the processor services the IRQ there is a new tasklet is getting created however the function remains the same.

module_init(my_generic_init); module_exit(my_generic_exit);

-------------------------------------------------------------------------

Above solution will not miss any bottom halves. Can somebody explains me why above solution is working ? What is so special about dynamic tasklets ?

The solution works because the new tasklet is created everytime with the same cb function. Note that the function should be fully re-entrant for such use-cases which is done using the local variable - arg/data in your case.

BR,Abhinav

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