linux-kernel - Re: [PATCH] ALSA: usb-audio: endpoint : remove redundant check before usb_free

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Message-ID: <s5him788hek.wl-tiwai@suse.de>
Date:   Thu, 04 Feb 2021 07:40:35 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Xu Wang <vulab@...as.ac.cn>
Cc:     perex@...ex.cz, tiwai@...e.com, alexander@...y.me,
        e.burema@...il.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: usb-audio: endpoint : remove redundant check before usb_free_coherent()

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