Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 04 Feb 2021 07:40:35 +0100
Message-ID: <s5him788hek.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Xu Wang <vulab@iscas.ac.cn>
Cc:     perex@perex.cz, tiwai@suse.com, alexander@tsoy.me,
        e.burema@gmail.com, alsa-devel@alsa-project.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ALSA: usb-audio: endpoint : remove redundant check before usb_free_coherent()
In-Reply-To: <20210204020518.76619-1-vulab@iscas.ac.cn>
References: <20210204020518.76619-1-vulab@iscas.ac.cn>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka)
 FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3
 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Thu, 04 Feb 2021 03:05:18 +0100,
Xu Wang wrote:
> 
> usb_free_coherent() is safe with NULL addr and this check is
> not required.

The check there isn't about NULL buffer or not; instead it checks
whether the buffer was allocated for each or it shares the single
buffer (for sync endpoints).  In the latter case, your patch will lead
to double-free.


thanks,

Takashi