linux-kernel - re: ALSA: control - add layer registration routines

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Date:   Wed, 31 Mar 2021 16:17:24 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Jaroslav Kysela <perex@...ex.cz>
Cc:     Takashi Iwai <tiwai@...e.com>, Mark Brown <broonie@...nel.org>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        alsa-devel@...a-project.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: ALSA: control - add layer registration routines

Hi,

Static analysis on linux-next with Coverity has detected a potential
issue in the following commit:

commit 3f0638a0333bfdd0549985aa620f2ab69737af47
Author: Jaroslav Kysela <perex@...ex.cz>
Date:   Wed Mar 17 18:29:41 2021 +0100

    ALSA: control - add layer registration routines

The static analysis is as follows:

2072 void snd_ctl_disconnect_layer(struct snd_ctl_layer_ops *lops)
2073 {
2074        struct snd_ctl_layer_ops *lops2, *prev_lops2;
2075
2076        down_write(&snd_ctl_layer_rwsem);

    assignment: Assigning: prev_lops2 = NULL.

2077        for (lops2 = snd_ctl_layer, prev_lops2 = NULL; lops2; lops2
= lops2->next)
2078                if (lops2 == lops) {

    null: At condition prev_lops2, the value of prev_lops2 must be NULL.
    dead_error_condition: The condition !prev_lops2 must be true.

2079                        if (!prev_lops2)
2080                                snd_ctl_layer = lops->next;
2081                        else

    'Constant' variable guards dead code (DEADCODE) dead_error_line:
    Execution cannot reach this statement: prev_lops2->next = lops->next;.
    Local variable prev_lops2 is assigned only once, to a constant
value, making it effectively constant throughout its scope. If this is
not the intent, examine the logic to see if there is a missing
assignment that would make prev_lops2 not remain constant.

2082                                prev_lops2->next = lops->next;
2083                        break;
2084                }
2085        up_write(&snd_ctl_layer_rwsem);
2086 }

I couldn't quite figure out the original intent of the prev_lops use, so
I'd thought I'd report this issue as the code does look incorrect.

Colin