On Thu, 21 Dec 2006 10:41:44 +0100 "Sorin Manolache" <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/