Re: [PATCH] kernel/async.c:introduce async_schedule*_atomic

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 12 May 2009 18:04:35 +0200,
Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Tue, May 12, 2009 at 05:44:58PM +0200, Frederic Weisbecker wrote:
> > On Tue, May 12, 2009 at 11:13:42PM +0800, tom.leiming@gmail.com wrote:
> > >   * Returns an async_cookie_t that may be used for checkpointing later.
> > > - * Note: This function may be called from atomic or non-atomic contexts.
> > > + * Note:This function may be called from non-atomic contexts,and not
> > > + * 	called from atomic contexts with safety. Please use
> > > + * 	async_schedule_atomic in atomic contexts.
> 
> 
> I suggest to add a comment which explains the reason for which it is unsafe
> to call it in atomic context: because the scheduled work might be synchronously
> executed.
> 
> One could believe this is because async_schedule() internally uses
> a function which might sleep whereas the actual problem may come
> from the scheduled function.

I'm wondering whether this is not mixing two different things up:
- Making async_schedule_* safe from an atomic context.
- Disallowing calling the function synchronously if asynchronous
  scheduling failed.

Perhaps we want async_schedule_nosync() in addition?

> 
> BTW, now that we have an atomic safe version, may be we could
> also adapt the kmalloc GFP flags subsequently?

Yes, that would make sense.