linux-kernel - Re: [PATCH v2 0/6] kernfs: proposed locking and concurrency improvement

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Message-ID: <X9t1xVTZ/ApIvPMg@mtj.duckdns.org>
Date:   Thu, 17 Dec 2020 10:14:13 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Ian Kent <raven@...maw.net>
Cc:     Fox Chen <foxhlchen@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        akpm@...ux-foundation.org, dhowells@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        miklos@...redi.hu, ricklind@...ux.vnet.ibm.com,
        sfr@...b.auug.org.au, viro@...iv.linux.org.uk
Subject: Re: [PATCH v2 0/6] kernfs: proposed locking and concurrency
 improvement

Hello,

On Thu, Dec 17, 2020 at 07:48:49PM +0800, Ian Kent wrote:
> > What could be done is to make the kernfs node attr_mutex
> > a pointer and dynamically allocate it but even that is too
> > costly a size addition to the kernfs node structure as
> > Tejun has said.
> 
> I guess the question to ask is, is there really a need to
> call kernfs_refresh_inode() from functions that are usually
> reading/checking functions.
> 
> Would it be sufficient to refresh the inode in the write/set
> operations in (if there's any) places where things like
> setattr_copy() is not already called?
> 
> Perhaps GKH or Tejun could comment on this?

My memory is a bit hazy but invalidations on reads is how sysfs namespace is
implemented, so I don't think there's an easy around that. The only thing I
can think of is embedding the lock into attrs and doing xchg dance when
attaching it.

Thanks.

-- 
tejun