Messages in this thread | | | Subject | Possible kernel lock in semaphore's __down() | From | Aleksandar Dezelin <> | Date | Wed, 29 Aug 2007 23:52:51 +0200 |
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Hi!
I'm a newbie here on the list and also as a "kernel hacker". There's a bug reported in bugzilla (Bug 7927), cite:
> In the function __down > > fastcall void __sched __down(struct semaphore * sem) > { > struct task_struct *tsk = current; > DECLARE_WAITQUEUE(wait, tsk); > unsigned long flags; > > tsk->state = TASK_UNINTERRUPTIBLE; > spin_lock_irqsave(&sem->wait.lock, flags); > add_wait_queue_exclusive_locked(&sem->wait, &wait); > ... > } > > > From this code fragment, it sets the tsk->state to TASK_UNINTERRUPTIBLE before > gets the spinlock. Assume at that moment, a interrupt ocuur and and after the > interrupt handle ends, an other process is scheduled to run (assume the kernel > is preemptalbe). In this case, the previous process ( its state has set to > TASK_UNINTERRUPTIBLE) has been picked off the run queue, and it has not yet add > to the wait queue( sem->wait ), so it may be never waited up forever. >
I have marked it as rejected as as I can see at the time this function is called, it is guaranteed that ret_from_intr() will not call schedule() on return from an interrupt handler to either kernel space or user space because of the call to macro might_sleep() in semaphore's down(). Am I wrong?
Thanks and best regards, Aleksandar Dezelin
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