linux-kernel - Re: [PATCH 04/10] staging: erofs: fix `erofs_workgroup_{try_to

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Message-ID: <20181122110534.GD5287@kroah.com>
Date:   Thu, 22 Nov 2018 12:05:34 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Gao Xiang <gaoxiang25@...wei.com>
Cc:     devel@...verdev.osuosl.org, linux-erofs@...ts.ozlabs.org,
        Chao Yu <yuchao0@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>, weidu.du@...wei.com,
        Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH 04/10] staging: erofs: fix
 `erofs_workgroup_{try_to_freeze, unfreeze}'

On Thu, Nov 22, 2018 at 06:29:34PM +0800, Gao Xiang wrote:
> Hi Greg,
> 
> On 2018/11/22 18:21, Greg Kroah-Hartman wrote:
> > On Tue, Nov 20, 2018 at 10:34:19PM +0800, Gao Xiang wrote:
> >> There are two minor issues in the current freeze interface:
> >>
> >>    1) Freeze interfaces have not related with CONFIG_DEBUG_SPINLOCK,
> >>       therefore fix the incorrect conditions;
> >>
> >>    2) For SMP platforms, it should also disable preemption before
> >>       doing atomic_cmpxchg in case that some high priority tasks
> >>       preempt between atomic_cmpxchg and disable_preempt, then spin
> >>       on the locked refcount later.
> > 
> > spinning on a refcount implies that you are trying to do your own type
> > of locking.  Why not use the in-kernel locking api instead?  It will
> > always do better than trying to do your own logic as the developers
> > there know locking across all types of cpus better than filesystem
> > developers :)
> 
> It is because refcount also plays a role as a spinlock on a specific value
> (== EROFS_LOCKED_MAGIC), no need to introduce such a value since the spin
> window is small.

As I said in another email, doing two things with one variable is odd as
those are two different types of functions.

greg k-h