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Date:   Mon, 22 Mar 2021 18:26:33 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Namjae Jeon <namjae.jeon@samsung.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-cifs@vger.kernel.org,
        linux-cifsd-devel@lists.sourceforge.net, smfrench@gmail.com,
        senozhatsky@chromium.org, hyc.lee@gmail.com, hch@lst.de,
        hch@infradead.org, ronniesahlberg@gmail.com,
        aurelien.aptel@gmail.com, aaptel@suse.com, sandeen@sandeen.net,
        dan.carpenter@oracle.com, colin.king@canonical.com,
        rdunlap@infradead.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steve French <stfrench@microsoft.com>
Subject: Re: [PATCH 3/5] cifsd: add file operations
Message-ID: <YFhiySJYbWW8bq6C@google.com>
References: <20210322051344.1706-1-namjae.jeon@samsung.com>
 <CGME20210322052207epcas1p3f0a5bdfd2c994a849a67b465479d0721@epcas1p3.samsung.com>
 <20210322051344.1706-4-namjae.jeon@samsung.com>
 <YFhBHScj4QxLl/Ef@zeniv-ca.linux.org.uk>
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On (21/03/22 07:02), Al Viro wrote:
> On Mon, Mar 22, 2021 at 02:13:42PM +0900, Namjae Jeon wrote:
> > +static struct ksmbd_file *__ksmbd_lookup_fd(struct ksmbd_file_table *ft,
> > +					    unsigned int id)
> > +{
> > +	bool unclaimed = true;
> > +	struct ksmbd_file *fp;
> > +
> > +	read_lock(&ft->lock);
> > +	fp = idr_find(ft->idr, id);
> > +	if (fp)
> > +		fp = ksmbd_fp_get(fp);
> > +
> > +	if (fp && fp->f_ci) {
> > +		read_lock(&fp->f_ci->m_lock);
> > +		unclaimed = list_empty(&fp->node);
> > +		read_unlock(&fp->f_ci->m_lock);
> > +	}
> > +	read_unlock(&ft->lock);
> > +
> > +	if (fp && unclaimed) {
> > +		atomic_dec(&fp->refcount);
> > +		return NULL;
> > +	}
>
> Can that atomic_dec() end up dropping the last remaining reference?

Yes, I think it should increment refcount only for "claimed" fp.