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Subject: Re: BUG: possible deadlock detected! (sound) [Was: 2.6.17-rc5-mm1]
From: Arjan van de Ven <arjan@infradead.org>
To: Jiri Slaby <jirislaby@gmail.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       alsa-devel@alsa-project.org, tiwai@suse.de,
       emu10k1-devel@lists.sourceforge.net, James@superbug.demon.co.uk,
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Date: Tue, 30 May 2006 13:06:28 +0200
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On Tue, 2006-05-30 at 147 +0159, Jiri Slaby wrote:

(I've turned your backtrace upside down to show it "chronological")

 [<c05911e0>] alsa_emu10k1_synth_init+0x22/0x24
 [<c0333d04>] snd_seq_device_register_driver+0x8f/0xeb

this one does:

       mutex_lock(&ops->reg_mutex);
       ...
       list_for_each(head, &ops->dev_list) {
                struct snd_seq_device *dev = list_entry(head, struct snd_seq_device, list);
                init_device(dev, ops);
       }
       mutex_unlock(&ops->reg_mutex);

 [<c0333537>] init_device+0x2c/0x94
  which calls into the driver
 [<c0352c39>] snd_emu10k1_synth_new_device+0xe7/0x14e
 [<c0353f50>] snd_emux_register+0x10d/0x13f
 [<c0358260>] snd_emux_init_seq_oss+0x35/0x9c
 [<c0333aa0>] snd_seq_device_new+0x96/0x111

and this one does
        mutex_lock(&ops->reg_mutex);
        list_add_tail(&dev->list, &ops->dev_list);
        ops->num_devices++;
        mutex_unlock(&ops->reg_mutex);


so... on first sight this looks like a real deadlock;
unless the ALSA folks can tell me why "ops" is always different,
and what the lock ordering rules between those is...


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