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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [BUG] ALSA: core: seq: a possible double-lock bug in
 snd_seq_midisynth_remove()
To:     perex@perex.cz, Takashi Iwai <tiwai@suse.de>,
        gregkh@linuxfoundation.org, rfontana@redhat.com,
        allison@lohutok.net, tglx@linutronix.de
Cc:     alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Message-ID: <50b3b4c4-fe36-8c65-345b-f0a51193726c@gmail.com>
Date:   Mon, 29 Jul 2019 11:54:07 +0800
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In snd_seq_midisynth_remove(), there is a possible double-lock bug:
snd_seq_midisynth_remove()
     mutex_lock(&register_mutex); -- line 421
     snd_seq_delete_kernel_client() --- line 436
         seq_free_client() -- line 2244
             mutex_lock(&register_mutex); -- line 294

This bug is found by a static analysis tool STCheck written by us.

I do not know how to correctly fix this bug, so I only report it.
A possible fix is to release the mutex lock before calling 
seq_free_client() in snd_seq_delete_kernel_client() and then acquiring 
the lock again after calling seq_free_client().


Best wishes,
Jia-Ju Bai