linux-kernel - Re: [RESEND PATCH v7 1/8] kernfs: Introduce interface to access global kernfs_open_file

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Message-ID: <87r16z191l.fsf@email.froward.int.ebiederm.org>
Date:   Fri, 18 Mar 2022 12:10:14 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Imran Khan <imran.f.khan@...cle.com>
Cc:     tj@...nel.org, viro@...iv.linux.org.uk, gregkh@...uxfoundation.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 1/8] kernfs: Introduce interface to access
 global kernfs_open_file_mutex.

Imran Khan <imran.f.khan@...cle.com> writes:

> This allows to change underlying mutex locking, without needing to change
> the users of the lock. For example next patch modifies this interface to
> use hashed mutexes in place of a single global kernfs_open_file_mutex.
>
> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>
> ---
>  fs/kernfs/file.c            | 26 +++++++++++++++-----------
>  fs/kernfs/kernfs-internal.h | 18 ++++++++++++++++++
>  2 files changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index 7aefaca876a0..99793c32abc3 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -30,7 +30,7 @@
>   * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
>   */
>  static DEFINE_SPINLOCK(kernfs_open_node_lock);
> -static DEFINE_MUTEX(kernfs_open_file_mutex);
> +DEFINE_MUTEX(kernfs_open_file_mutex);
^^^^^????

Why when you want things more localized are you making a lock more
global?
> diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
> index eeaa779b929c..df00a5f5a367 100644
> --- a/fs/kernfs/kernfs-internal.h
> +++ b/fs/kernfs/kernfs-internal.h
> @@ -164,4 +164,22 @@ void kernfs_drain_open_files(struct kernfs_node *kn);
>   */
>  extern const struct inode_operations kernfs_symlink_iops;
>  
> +extern struct mutex kernfs_open_file_mutex;
> +
> +static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
> +{
> +	return &kernfs_open_file_mutex;
> +}
> +
> +static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
> +{
> +	struct mutex *lock;
> +
> +	lock = kernfs_open_file_mutex_ptr(kn);
> +
> +	mutex_lock(lock);
> +
> +	return lock;
> +}

Why don't these functions live in fs/kern/fs/file.c

Eric