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From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Subject: Regmap commit 815806e3 from 4.8-rc6 introduces a deadlock
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Date: Thu, 22 Sep 2016 11:32:33 +0300
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Hi.

Here is a trace:

amixer          D 8068ae98     0   197    183 0x00000000
Backtrace: 
[<8068ab7c>] (__schedule) from [<8068b1c4>] (schedule+0xb8/0xd0)
[<8068b10c>] (schedule) from [<8068b61c>] (schedule_preempt_disabled+0x20/0x2c)
[<8068b5fc>] (schedule_preempt_disabled) from [<8068cd18>] (__mutex_lock_slowpath+0xf8/0x180)
[<8068cc20>] (__mutex_lock_slowpath) from [<8068cde0>] (mutex_lock+0x40/0x58)
[<8068cda0>] (mutex_lock) from [<8047c440>] (regmap_lock_mutex+0x18/0x1c)
[<8047c428>] (regmap_lock_mutex) from [<8047fedc>] (regcache_drop_region+0x44/0x144)
[<8047fe98>] (regcache_drop_region) from [<8047f0a4>] (_regmap_raw_write+0x65c/0x7f0)
[<8047ea48>] (_regmap_raw_write) from [<8047f2b8>] (_regmap_bus_raw_write+0x80/0x98)
[<8047f238>] (_regmap_bus_raw_write) from [<8047dea4>] (_regmap_write+0x11c/0x16c)
[<8047dd88>] (_regmap_write) from [<8047dfa4>] (_regmap_update_bits+0xb0/0xd4)
[<8047def4>] (_regmap_update_bits) from [<8047f460>] (regmap_update_bits_base+0x60/0x84)
[<8047f400>] (regmap_update_bits_base) from [<805acecc>] (snd_soc_component_update_bits+0x40/0x5c)
[<805ace8c>] (snd_soc_component_update_bits) from [<805adec0>] (snd_soc_put_volsw+0x9c/0xf8)
[<805ade24>] (snd_soc_put_volsw) from [<8058b070>] (snd_ctl_ioctl+0x75c/0xbe8)
[<8058a914>] (snd_ctl_ioctl) from [<80209d04>] (vfs_ioctl+0x30/0x44)
[<80209cd4>] (vfs_ioctl) from [<8020a5ec>] (do_vfs_ioctl+0x7b0/0x884)
[<80209e3c>] (do_vfs_ioctl) from [<8020a704>] (SyS_ioctl+0x44/0x6c)
[<8020a6c0>] (SyS_ioctl) from [<80107900>] (ret_fast_syscall+0x0/0x3c)


Regmap lock is taken in regmap_update_bits_base() and then
regcache_drop_region() added in commit 815806e3 tries to take it again.


WBR,
Nikita