linux-kernel - Re: [PATCH 2/4] percpu-rwsem: introduce percpu_rwsem_release() and percpu_rwsem

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Date:	Fri, 31 Jul 2015 12:20:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jan Kara <jack@...e.cz>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] percpu-rwsem: introduce percpu_rwsem_release() and
 percpu_rwsem_acquire()

On Wed, Jul 22, 2015 at 11:15:35PM +0200, Oleg Nesterov wrote:
> Add percpu_rwsem_release() and percpu_rwsem_acquire() for the users
> which need to return to userspace with percpu-rwsem lock held and/or
> pass the ownership to another thread.
> 
> TODO: change percpu_rwsem_release() to use rwsem_clear_owner(). We can
> either fold kernel/locking/rwsem.h into include/linux/rwsem.h, or add
> the non-inline percpu_rwsem_clear_owner().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  include/linux/percpu-rwsem.h |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
> index 3ebf982..06af654 100644
> --- a/include/linux/percpu-rwsem.h
> +++ b/include/linux/percpu-rwsem.h
> @@ -33,4 +33,23 @@ extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
>  	__percpu_init_rwsem(brw, #brw, &rwsem_key);		\
>  })
>  
> +
> +#define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
> +
> +static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
> +					bool read, unsigned long ip)
> +{
> +	lock_release(&sem->rw_sem.dep_map, 1, ip);
> +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
> +	if (!read)
> +		sem->rw_sem.owner = NULL;
> +#endif
> +}
> +
> +static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
> +					bool read, unsigned long ip)
> +{
> +	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
> +}

This is of course entirely vile.. Can't we open code that in the freezer
code? Having helpers here might give some people the impression that
this is a sane thing to do.

Also, when you do that in the freezer, put a big honking comment on it.

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