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

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Message-ID: <6919f0a9-b3e0-b5c3-0669-4b84beed84a6@oracle.com>
Date:   Mon, 21 Mar 2022 11:10:09 +1100
From:   Imran Khan <imran.f.khan@...cle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.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.

Hello Eric,

Thanks for reviewing this.

On 19/3/22 4:10 am, Eric W. Biederman wrote:
> Imran Khan <imran.f.khan@...cle.com> writes:
> 
[...]
>>  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?

The idea was to keep the interface in kernfs-internal.h. But since this
mutex is used only in kernfs/file.c, I can keep the mutex static and
bring interfaces that access this mutex in kernfs/file.c. This will
cover your other query as well.

>> 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
> 

I can put these in kernfs/file.c. Please see earlier comment.

Thanks,
 -- Imran