Re: [RFC,PATCH] use rcu for fasync_lock

Manfred Spraul
2003-12-21T21:08:43Z

Linus Torvalds wrote:

>On Sun, 21 Dec 2003, Manfred Spraul wrote:
>
>
>>Initially I tried to keep the patch as tiny as possible, thus I avoided
>>adding an inline function. But Stephen Hemminger convinced me to update
>>the network code, and thus it didn't matter and I've switched to an
>>inline function.
>>What do you think about the attached patch?
>>
>>
>
>Please, NO!
>
>Stuff like this
>
> - write_lock_irq(&fasync_lock);
> + if (s)
> + lock_sock(s);
> + else
> + spin_lock(&fasync_lock);
> +
>
>should not be allowed. That's especially true since the choice really is a
>static one depending on the caller.
>
>Just make the caller do the locking.
>
>
It's not that simple: the function does
kmalloc();
spin_lock();
use_allocation.
If the caller does the locking, then the kmalloc would have to use
GFP_ATOMIC, or the caller would have to do the alloc.
But: as far as I can see, these lines usually run under lock_kernel().
If this is true, then the spin_lock(&fasync_lock) won't cause any
scalability regression, and I'll use that lock instead of lock_sock,
even for network sockets.

--
Manfred