Messages in this thread | | | Date | Thu, 21 Dec 2006 11:05:51 +0100 | From | Paolo Ornati <> | Subject | Re: newbie questions about while (1) in kernel mode and spinlocks |
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On Thu, 21 Dec 2006 10:41:44 +0100 "Sorin Manolache" <sorinm@gmail.com> wrote:
> The Linux Device Drivers book says that a spin_lock should not be > shared between a process and an interrupt handler. The explanation is > that the process may hold the lock, an interrupt occurs, the interrupt > handler spins on the lock held by the process and the system freezes. > Why should it freeze? Isn't it possible for the interrupt handler to > re-enable interrupts as its first thing, then to spin at the lock, the > timer interrupt to preempt the interrupt handler and to relinquish > control to the process which in turn will finish its critical section > and release the lock, making way for the interrupt handler to > continue.
Iterrupt handlers are executend in the process context (on top of the process that they interrupted).
So, if you have a proccess A that does:
Usual Kernel Code Interrupt Handler
... spin_lock(my_lock); ... -------interrupt-----> ... spin_lock(my_lock); // deadlock! ... <------ back --------- ---- spin_unlock(my_lock);
See?
If the interrupt comes in when process A is running and holding the lock PREEMPTION can't do anything.
-- Paolo Ornati Linux 2.6.20-rc1-g99f5e971 on x86_64 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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