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SubjectRe: adding to wait queue

On Mon, 7 Jun 1999, Raj, Ashok wrote:

> Have a silly question.
>
> when i add to wait_queue() should i need a spinlock around it in a MP
> system? or
> would doing a
>
> save_flags(); cli() before doing a add_wait_queue() be sufficient.

add_wait_queue()/remove_wait_queue() functions are MP-safe. So for the
'typical' case where the waitqueue is on the local kernel stack you need
no locking at all. The generic rule is that typically all kernel services
are MP-safe (get_free_pages(), kmalloc(), slab, signal sending, etc.)

[in some cases we use __add_waitqueue which is a non-spinlock version, in
that case we have to make sure to hold the spinlock - the majority of uses
doesnt have to do this]

-- mingo


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