Workqueues vs. kernel threads for processing asynchronous socket events

Workqueues vs. kernel threads for processing asynchronous socket events

[Martin Lucina]

Hi,

I'm trying to find the best mechanism to process events from kernel space
sockets in an asynchronous manner. The work in progress code I have at the
moment tries to at least call kernel_accept() on a bound TCP socket when it
gets called by the underlying sk->sk_data_ready callback.

The current approach I have is to use a workqueue and try to schedule work
inside the callback, but this has the kernel complaining about "scheduling
while atomic", so it doesn't look like it's the right approach? Am I
allowed to call schedule_work() from the context of a sk->sk_data_ready
callback or not?

Sunrpc/knfsd appears to use a different approach where
svc_tcp_listen_data_ready() sets the appropriate state and then calls
wake_up_interruptible_all(sk_sleep(sk)) -- it's not clear who this is
waking up, the nfsd kernel thread or someone else?

Any advice on what is the best future-proof approach to use for this kind
of thing in a new project?

-mato

Re: Workqueues vs. kernel threads for processing asynchronous socket events

[Martin Sustrik]

On 12/10/2010 04:27 PM, Martin Lucina wrote:

> I'm trying to find the best mechanism to process events from kernel space
> sockets in an asynchronous manner. The work in progress code I have at the
> moment tries to at least call kernel_accept() on a bound TCP socket when it
> gets called by the underlying sk->sk_data_ready callback.
>
> The current approach I have is to use a workqueue and try to schedule work
> inside the callback, but this has the kernel complaining about "scheduling
> while atomic", so it doesn't look like it's the right approach? Am I
> allowed to call schedule_work() from the context of a sk->sk_data_ready
> callback or not?

It turns out that the issue was caused by kmalloc(GFP_KERNEL) in the 
callback function, not the schedule_work() function. Using GFP_ATOMIC 
instead solves the problem.

Sorry for the annoyance.
Martin