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SubjectRe: kmalloc without GFP_xxx?


On Wed, 29 Jun 2005, Arjan van de Ven wrote:
> >
> > but it sets irqs_disabled() IIRC.
>
> only spin_lock_irq() and co do.
> not the simple spin_lock()
>

It may be dangerous to use spin_lock with interrupts enabled, since you
have to make sure that no interrupt ever grabs that lock. Although I do
recall seeing a few locks like this. But even so, you can transfer the
latency of the interrupts going off while holding that lock to another CPU
which IMHO is a bad thing. Also a simple spin_lock would disable
preemption with CONFIG_PREEMPT set and that would make in_atomic fail.
But to implement a kmalloc_auto you would always need to have a preempt
count.

I'm not for a kmalloc_auto, but something like it would be useful for a
function that can work for either context, and just fail nicely if the
ATOMIC is set and the malloc can't get memory. A function like this would
currently have to always use ATOMIC even if it could have used KERNEL for
some scenarios, since it would suffer the same pitfalls as a kmalloc_auto
in determining its context.

-- Steve

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