[dm-devel] [patch 2/4] swait: export the symbols __prepare_to_swait and __finish_swait

[Mike Snitzer]

On Tue, May 22 2018 at  2:34am -0400,
Christoph Hellwig <hch at infradead.org> wrote:

> On Sat, May 19, 2018 at 07:25:05AM +0200, Mikulas Patocka wrote:
> > In order to reduce locking overhead, I use the spinlock in
> > swait_queue_head to protect not only the wait queue, but also the list of
> > events. Consequently, I need to use unlocked functions __prepare_to_swait
> > and __finish_swait. These functions are declared in the file
> > include/linux/swait.h, but they are not exported, and so they are not
> > useable from kernel modules.
> 
> Please CC the author and maintainers of the swait code.
> 
> My impression is that this is the wrong thing to do.  The swait code
> is supposed to be simple and self contained, and if you want to do
> anything else use normal waitqueues.

You said the same thing last time around.  I've since cc'd Peter and
Thomas and haven't heard back, see:
https://www.redhat.com/archives/dm-devel/2018-May/msg00048.html

The entire point of exporting these symbols is to allow use of the
"simple waitqueue" code to optimize -- without resorting to using normal
waitqueues.

Mike