linux-kernel - Re: [V9fs-developer] [PATCH] net/9p/client.c: put refcount of trans_mod in error case in parse

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Date:   Mon, 9 Jul 2018 16:29:20 +0200
From:   Greg Kurz <groug@...d.org>
To:     piaojun <piaojun@...wei.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        <ericvh@...il.com>, <rminnich@...dia.gov>, <lucho@...kov.net>,
        v9fs-developer@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [V9fs-developer] [PATCH] net/9p/client.c: put refcount of
 trans_mod in error case in parse_opts()

On Fri, 6 Jul 2018 17:42:56 +0800
piaojun <piaojun@...wei.com> wrote:

> From my test, the second mount will fail after umounting successfully.
> The reason is that we put refcount of trans_mod in the correct case rather
> than the error case in parse_opts() at last. That will cause the refcount
> decrease to -1, and when we try to get trans_mod again in
> try_module_get(), we could only increase refcount to 0 which will cause
> failure as follows:
> parse_opts
>   v9fs_get_trans_by_name
>     try_module_get : return NULL to caller which cause error
> 
> So we should put refcount of trans_mod in error case.
> 
> Fixes: 9421c3e64137ec ("net/9p/client.c: fix potential refcnt problem of trans module")
> 
> Signed-off-by: Jun Piao <piaojun@...wei.com>
> ---

Reviewed-by: Greg Kurz <groug@...d.org>

>  net/9p/client.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 18c5271..5c13431 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -225,7 +225,8 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>  	}
> 
>  free_and_return:
> -	v9fs_put_trans(clnt->trans_mod);
> +	if (ret)
> +		v9fs_put_trans(clnt->trans_mod);
>  	kfree(tmp_options);
>  	return ret;
>  }