On Wed, Oct 7, 2009 at 12:04 PM, Jason Nymble <jason.nymble@xxxxxxxxx> wrote:
Just asking, spin_lock will disable preemption, but it can't disable interrupts. So, a higher priority process can't preempt lower priority process.
Second,
Interrupts are nothing to do with preemption. Interrupt handlers can preempt a process unless it is not disable ( of course via spin_lock_irq or spin_lock_irq_save api).
On 07 Oct 2009, at 7:47 AM, er krishna wrote:Rajat San,
Just asking (since i didn't see spinlock implementation in kernel src),
On Tue, Oct 6, 2009 at 5:52 PM, Rajat Jain <Rajat.Jain@xxxxxxxxxxxx> wrote:
Hello Govind,
This is not possible. Spin lock APIs disable kernel preemption
> What happens when you go for spin locks without
> disabling kernel preemption? Suppose you acquire
> a spin lock in a system call handler (a service
> routine on behalf of a user mode process) with
> kernel preemption enabled.
automatically.
Spin lock APIs disables kernel preemption in all its api or some specific apis only. Please confirm and elaborate.
There are a few variants of the spin lock APIs. See the link which various people have posted for details:The most basic spin_lock() does not disable scheduling or interrupts etc., so must be avoided for synchronization between a syscall and an interrupt context otherwise you will get deadlock. spin_lock_irqsave() disables all pre-emptive scheduling and interrupts AFAIK, so it would be safe.
Just asking, spin_lock will disable preemption, but it can't disable interrupts. So, a higher priority process can't preempt lower priority process.
Second,
Interrupts are nothing to do with preemption. Interrupt handlers can preempt a process unless it is not disable ( of course via spin_lock_irq or spin_lock_irq_save api).
I think it is generally preferable to avoid using spin_lock_irqsave() if possible by deferring your interrupt work to a tasklet (in which you can use spin_lock_bh to sync to your syscall) or a workqueue (in which you can use a semaphore to sync to your syscall). Even better would be to use lockless algorithms or data structures if possible. In general, if you must use a spinlock, try to keep it limited to a very small piece of code to reduce lock contention. Also, enable kernel debugging and specifically the options about lock checking, these can help a great deal to debug issues. I hope the aforementioned information is correct and doesn't lead you astray...
