Hi, On 8/30/06, Rajat Jain <rajat.noida.india@xxxxxxxxx> wrote:
On 8/30/06, Rik van Riel <riel@xxxxxxxxxxx> wrote: > Rick Brown wrote: > > Hi, > > > > In my driver (Process context), I have written the following code: > > > > -------------------------------------------- > > spin_lock(lock) > > ... > > //Critical section to manipulate driver data > > ... interrupt hits here > interrupt handler tries to grab the spinlock, which is already taken > *BOOM* > > > spin_u lock(lock) > > --------------------------------------------- > > The interrupt handler TRIES to grab the spinlock, which is already taken. Why will it "BOOM"? Wouldn't the interrupt handler busy wait, waiting for the lock?
If you take spin_lock in interrupt as well as in process context then-: 1. On UP non-preempt kernel: There will be no locks taken, so nothing is gonna protect the shared data between the interrupt handler & process context thread. 2. On the UP preempt kernel: The lock has been taken by the process context, and now if the interrupts is issued, it will try to grab the same lock, but it will never get it ... and nobody is going to leave that lock. boom* - Deadlock. 3. On SMP machine non-preempt kernel: The locks will be taken but no protection against the interrupt as such. 4. On SMP preempt kernel: process context threads are synchronised but not the interrupts.
> > I have written similar code in my interrupt handler (Interrupt > > context). The driver data is not accessed from anywhere else. Is my > > code safe from any potential concurrency issues? Is there a need to > > use spin_lock_irqsave()? In both the places? > > You need to use spin_lock_irqsave() from process context. > From the interrupt handler itself it doesn't hurt, but it > shouldn't matter much since interrupt handlers should not > get preempted.
Yes, AFAIK the correct idea is to take spin_lock() in interrupt handler (Here I consider that your interrupt is already disabled.) And take spin_lock_irq() or spin_lock_irqsave() lock from the process context. --v -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
