Subject: Re: linux-next: build failure after merge of the rcu tree

From: "Paul E. McKenney" <[email-masked]>
Date: Wed, 11 Dec 2019 20:07:37 -0800

On Thu, Dec 12, 2019 at 01:45:16PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the rcu tree, today's linux-next build (x86_64 allmodconfig)
> failed like this:
> 
> drivers/misc/watch_queue.c: In function 'watch_queue_set_filter':
> drivers/misc/watch_queue.c:526:2: error: implicit declaration of function 'rcu_swap_protected' [-Werror=implicit-function-declaration]
>   526 |  rcu_swap_protected(wqueue->filter, wfilter,
>       |  ^~~~~~~~~~~~~~~~~~
> 
> Caused by commit
> 
>   af8c9224182e ("rcu: Remove rcu_swap_protected()")
> 
> interacting with commit
> 
>   fe78d401ca6b ("General notification queue with user mmap()'able ring buffer")
> 
> from the keys tree.
> 
> I have added the following merge fix patch for today:
> 
> From: Stephen Rothwell <[email-masked]>
> Date: Thu, 12 Dec 2019 13:37:52 +1100
> Subject: [PATCH] rcu: fix up for "Remove rcu_swap_protected()"
> 
> Signed-off-by: Stephen Rothwell <[email-masked]>

Reviewed-by: Paul E. McKenney <[email-masked]>

I would be happy to take this if desired, but it would probably be better
for this to be applied directly to the keys tree.  Either way, please let
me know.

							Thanx, Paul

> ---
>  drivers/misc/watch_queue.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/watch_queue.c b/drivers/misc/watch_queue.c
> index b3fc59b4ef6c..a4a77ec977ac 100644
> --- a/drivers/misc/watch_queue.c
> +++ b/drivers/misc/watch_queue.c
> @@ -523,8 +523,8 @@ static long watch_queue_set_filter(struct inode *inode,
>  	kfree(tf);
>  set:
>  	inode_lock(inode);
> -	rcu_swap_protected(wqueue->filter, wfilter,
> -			   lockdep_is_held(&inode->i_rwsem));
> +	wfilter = rcu_replace_pointer(wqueue->filter, wfilter,
> +				      lockdep_is_held(&inode->i_rwsem));
>  	inode_unlock(inode);
>  	if (wfilter)
>  		kfree_rcu(wfilter, rcu);
> -- 
> 2.24.0
> 
> -- 
> Cheers,
> Stephen Rothwell