[Devel] Re: [PATCH 06/14] sysfs: Rewrite sysfs_get_dentry

[Tejun Heo]

Eric W. Biederman wrote:
> Tejun Heo <htejun at gmail.com> writes:
> 
>> Hello, Eric.
>>
>> Eric W. Biederman wrote:
>>> I will look a little more and see.  But right now it looks like the
>>> real problem with locking is that we use sysfs_mutex to lock the
>>> sysfs_dirent s_children list.
>>>
>>> Instead it really looks like we should use i_mutex from the appropriate
>>> inode.  Or is there a real performance problem with forcing the directory
>>> inodes in core when we modify the directories?
>> I don't think there is any performance problem.  Problems with using
>> i_mutex were...
>>
>> * It was messy.  I don't remember all the details now but IIRC symlink
>> walk code was pretty complex.
>>
>> * And more importantly, inodes are reclaimable and might or might not be
>> there.
> 
> Yes.  But we can always force inodes into the cache when we need them.
> When I complete it I will have to show you a patch using the inode lock
> for locking directory modifications.  From what I can tell so far it allows
> me to fix the weird lock order problems and generally simplify the locking.

Hmmm... I think we can live with a bit of complexity in
sysfs_get_dentry().  It's very well localized and not even long.  I have
been trying hard to untangle sysfs internals from vfs and have a bit of
resistance against going back.  But, then again, if we can achieve
something better and simpler, why not?

-- 
tejun
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