Re: spinlocks

[Jeff Garzik]

"Ashutosh S. Rajekar" wrote:
> 
> Hello,
> 
> Are there any pitfalls in using critical code locked through spinlocks,
> inside a pair of lock_kernel()/unlock_kernel() calls on an SPM machine ?
> I'm not familiar with SMP machines, hence the question.
> 
> Say we have the following code: is it safe, or should I use the classical
> save_flags(), cli(), restore_flags() stuff ?

Read linux/Documentation/spinlocks.txt.

Basically, critical sections should usually be
spin_[un]lock_irq{save,restore}.  This even evaluates down to
save_flags/cli/restore_flags on UP.

If your critical section need not be guarded against interrupts, you can
use the simpler and faster spin_[un]lock variants.

there are also reader/writer spinlocks, if your device accesses follow
that pattern.

	jeff

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Jeff Garzik         | Only so many songs can be sung
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