Emmanuel Michon wrote:
>
> Hi,
>
> I read various documents about spinlocks, including Linux device
> drivers by A.Rubini 2nd edition, Unreliable guide to locking by P.R.Russel,
> and the source code of mainly network device drivers.
>
> I'm trying to achieve correct SMP synchronization on the Sigma Designs
> EM84xx; this one involves an extra small hardware interrupt (let's call it tophalf),
> only one tasklet scheduled at end of tophalf, and usual kernel side code of
> ioctl() I call usercontext.
>
> tophalf and tasklet are potentially writing the same data X
>
> tasklet and usercontext are potentially writing the same data Y
>
> So, my first guess was to use two spinlocks, X_lock and Y_lock,
Tasklets are run in interrupt context. You need the irq versions of the
spinlock in kernel space. In tasklet space a simple spinlock should be
enough as the tasklet can not be reentered.
-g
>
> with
>
> tophalf()
> {
> spin_lock(&X_lock);
> write X
> spin_unlock(&X_lock);
> }
>
> tasklet()
> {
> unsigned long flags;
> spin_lock_irqsave(&X_lock,flags);
> write X
> spin_lock(&Y_lock);
> write X, write Y
> spin_unlock(&Y_lock);
> write X
> spin_unlock_irqrestore(&X_lock,flags);
> }
>
> ioctl()
> {
> spin_lock_bh(&Y_lock);
> write Y ... maybe copy_from_user/copy_to_user
> spin_unlock_bh(&Y_lock);
> }
>
> So far I get really hardcore freezes and I'm trying to handle this with kgdb
>
> 1. Should I use spin_lock(&Y_lock); or spin_lock_bh(&Y_lock); in the tasklet body?
>
> 2. What is the reality behind: ``things which sleep'', is it really a problem
> to use copy_from_user/copy_to_user holding a spinlock?
>
> 3. Previous version used one semaphore to serialize usercontext access
> down_interruptible(&sem)/up(&sem)
> and handle tasklet concurrency with:
> down_trylock(&sem)/up(&sem)
>
> That allowed to catch signals (^C) with the usual -ERESTARTSYS stuff. As
> far as I understand, spinlocks allow the serialization but no way to interrupt
> a dead system call --- should I keep the semaphore only for this purpose?
>
> Sincerely yours,
>
> --
> Emmanuel Michon
> Chef de projet
> REALmagic France SAS
> Mobile: 0614372733 GPGkeyID: D2997E42
> -
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This archive was generated by hypermail 2b29 : Tue Apr 30 2002 - 22:00:13 EST