[RFC] down and down_interruptible on x86

["BALBIR SINGH" <balbir.singh@wipro.com>]

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Hello, All,

I am a little confused about down and down_interruptible.
My mixed mind tells me it might be a bug in __down() and
__down_interruptible()

snippet from semaphore.c

int __down_interruptible(struct semaphore * sem)
{
....

                /*
                 * With signals pending, this turns into
                 * the trylock failure case - we won't be
                 * sleeping, and we* can't get the lock as
                 * it has contention. Just correct the count
                 * and exit.
                 */
                if (signal_pending(current)) {
                        retval = -EINTR;
                        sem->sleepers = 0;
                        atomic_add(sleepers, &sem->count);
                        break;
                }
.....

        spin_unlock_irq(&semaphore_lock);
        tsk->state = TASK_RUNNING;
        remove_wait_queue(&sem->wait, &wait);
        wake_up(&sem->wait);                     <---------------------
Is this correct?
        return retval;
}

Lets assume that two processes/threads called down_interruptible on a
semaphore.

P1							P2
---			                        ---

down_interruptible()			down_interruptible()
 |							 |
 V							 V
Did not get semaphore, so		signals pending, so leave (break
in the signal_pending if)
waits in the wait queue
 |							|
 V							V
schedule()					Remove self from
wait_queue
							|
							V
						Call wake_up on
&sem->wait

Wont wake_up(&sem->wait), wakeup p1, so then when up() is called for
waking up P1,
the system will panic.

Am I missing something?

Warm Regards,
Balbir


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