On Tue, Mar 02, 2010 at 09:32:16AM +0530, Manish Katiyar wrote:
> Hello all,
>
> Is the following code valid ???
>
> foo() {
> ...........
> spin_lock(lock);
> ptr = kzalloc(size, GFP_KERNEL);
> spin_unlock(lock);
> .....
> }
You can't because GFP_KERNEL involves the fact
kzalloc might sleep while looking for memory
somewhere (swapping out pages to get some free
rooms).
And sleeping while holding a spinlock may
lead to a deadlock:
Task A holds spinlock in cpu0. Task A sleeps.
Task B is scheduled in cpu0, tries to take the
spinlock and then deadlock for ever.
You can use GFP_ATOMIC instead, but it's usually
not recommended as the GFP_ATOMIC pool is a pretty
limited resource.
The best is to allocate before you take the spinlock.
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