RE: Need for a new spinlock API?

[GAggarwal@IN.Safenet-inc.com]

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Hi Rajat,

I think spin_lock_irqsave() will fulfill the purpose as otherwise it may be
possible that the when a data structure is accessed in process context by
taking spin_lock and an interrupt comes then the ISR will remain in forever
loop waiting for the process context to release the lock result in a
deadlock situation for a uniprocessor system. You can also use
spin_lock_bh() if the data structure is accessed in tasklet (bottom half).
Please CMIIW.

--
Regards,
Gaurav Aggarwal


-----Original Message-----
From: kernelnewbies-bounce@nl.linux.org
[mailto:kernelnewbies-bounce@nl.linux.org]On Behalf Of Rajat Jain
Sent: Wednesday, April 04, 2007 8:57 AM
To: Arjan van de Ven
Cc: kernel mail; newbie
Subject: Re: Need for a new spinlock API?


> > We often have a case where a driver wants to access its data structure
> > in process context as well as in interrupt context (in its ISR). In
> > such scenarios, we generally use spin_lock_irqsave() to grab the lock
> > as well as disable all the local interrupts. AFAIK, disabling of local
> > interrupts is required so as to avoid running your ISR (which needs
> > the lock) while process context is holding the lock. However, this
> > also disables any other ISRs (which DO NOT need the lock) on the local
> > processor.
> >
> > Isn't this sub-optimal? Shouldn't there be a finer grained locking?
>
> actually it's optimal.
> It's fastest to delay the interrupts a little and be done with what you
> want to do under the lock quickly, and THEN take the interrupt. This
> means the lock hold time is short, which significantly reduces
> contention on this lock...

So on the same lines, if a data structure is accessed in both process
context and in a (single) driver ISR, should a driver use
spin_lock_irqsave() to get the lock in ISR? Or will a simple
spin_lock()  suffice?

Thanks,

Rajat


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