linux-kernel - Re: [PATCH v2] erofs: convert workstn to XArray

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Date:   Wed, 19 Feb 2020 16:04:57 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Chao Yu <yuchao0@...wei.com>
CC:     <linux-erofs@...ts.ozlabs.org>,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH v2] erofs: convert workstn to XArray

Hi Chao,

On Wed, Feb 19, 2020 at 03:46:16PM +0800, Chao Yu wrote:
> On 2020/2/17 11:30, Gao Xiang wrote:

[]

> > -	return err;
> > +	sbi = EROFS_SB(sb);
> > +repeat:
> > +	xa_lock(&sbi->managed_pslots);
> > +	pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
> > +			   NULL, grp, GFP_NOFS);
> > +	if (pre) {
> 
> It looks __xa_cmpxchg() could return negative value in case of failure, e.g.
> no memory case. We'd better handle that case and old valid workgroup separately?

Thanks, that is a quite good catch!

To be honest, I'm not quite sure whether __xa_cmpxchg
could fail due to no memory here (as a quick scan, it
will do __xas_nomem loop interally.)

But anyway, it needs bailing out all potential errors
by using xa_is_err(). Will do some research and send
v3 then.

Thanks,
Gao Xiang