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    SubjectRe: kernel panic with simple driver
    On 10/08/11 10:16, Murali K. Vemuri wrote:
    > Hello there,
    >
    > I have a small driver code with which I am randomly receiving kernel
    > panic. Can someone help me what is the mistake here?
    > The kernel panic is exactly caught to be at "add_timer (&my_timer) ".
    > I am able to get the print "Kicking off the timer" when the panic
    > happens.

    It helps to post the panic message. Its hard to debug problems without them.

    Where in add_timer is the panic occurring? It's only two lines, and one
    of those is a BUG_ON. Are you hitting that? The other line is a call to
    mod_timer and dereferences the timer pointer. Is the timer_list struct
    you are passing to add_timer sane?

    > Also, I could not observe any specific pattern in which the panic
    > occurs. But it is purely random. So far I was able to reproduce the
    > panic thrice out of 100+ attempts.

    Do you have any concurrent access to the timer? If so you may be racing
    on the between the test of timer_pending and the call to timer_add. In
    general, I think you should call mod_timer rather than add_timer (see
    the documentation in kernel/timer.c).

    ~Ryan

    > In all other attempts, my_dev_ioctl is called correctly and works correctly.
    >
    > struct timer_list my_timer;
    >
    > static int my_dev_ioctl(struct inode *inode, struct file *file,
    > unsigned int cmd, unsigned long arg)
    > {
    > switch(cmd)
    > {
    > case MATCH_CASE:
    > if (timer_pending (&my_timer))
    > {
    > printk(KERN_ERR "Timer currently pending, not adding
    > any more\n");
    > }
    > else
    > {
    > printk(KERN_ERR "Kicking off the timer\n");
    > add_timer(&my_timer);
    > }
    > break;
    > default:
    > break;
    > }
    > return 0;
    > }
    >
    > static struct miscdevice my_dummy_dev =
    > {
    > .minor = MISC_DYNAMIC_MINOR,
    > .name = "dummy_dev",
    > .fops =&my_dev_fops,
    > };
    >
    > static int __init my_dev_init(void)
    > {
    > /*initialize some GPIOs */
    > init_timer (&my_timer);
    > my_timer.data = 0;
    > my_timer.expires = jiffies + msecs_to_jiffies(500);
    > my_timer.function = ring_led_detect_timer;
    > misc_register(&mbi5025_dev);
    > }
    > module_init(my_dev_init);
    >
    >
    > Thanks in advance
    > Murali
    > --
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