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    Subject[PATCH 4.0 30/72] ALSA: emux: Fix mutex deadlock at unloading
    Date
    4.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Takashi Iwai <tiwai@suse.de>

    commit 07b0e5d49d227e3950cb13a3e8caf248ef2a310e upstream.

    The emux-synth driver has a possible AB/BA mutex deadlock at unloading
    the emu10k1 driver:

    snd_emux_free() ->
    snd_emux_detach_seq(): mutex_lock(&emu->register_mutex) ->
    snd_seq_delete_kernel_client() ->
    snd_seq_free_client(): mutex_lock(&register_mutex)

    snd_seq_release() ->
    snd_seq_free_client(): mutex_lock(&register_mutex) ->
    snd_seq_delete_all_ports() ->
    snd_emux_unuse(): mutex_lock(&emu->register_mutex)

    Basically snd_emux_detach_seq() doesn't need a protection of
    emu->register_mutex as it's already being unregistered. So, we can
    get rid of this for avoiding the deadlock.

    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/synth/emux/emux_seq.c | 2 --
    1 file changed, 2 deletions(-)

    --- a/sound/synth/emux/emux_seq.c
    +++ b/sound/synth/emux/emux_seq.c
    @@ -124,12 +124,10 @@ snd_emux_detach_seq(struct snd_emux *emu
    if (emu->voices)
    snd_emux_terminate_all(emu);

    - mutex_lock(&emu->register_mutex);
    if (emu->client >= 0) {
    snd_seq_delete_kernel_client(emu->client);
    emu->client = -1;
    }
    - mutex_unlock(&emu->register_mutex);
    }





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