Regmap commit 815806e3 from 4.8-rc6 introduces a deadlock

Regmap commit 815806e3 from 4.8-rc6 introduces a deadlock

[Nikita Yushchenko]

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

[PATCH] regmap: fix deadlock on _regmap_raw_write() error path

[Nikita Yushchenko]

Commit 815806e39bf6 ("regmap: drop cache if the bus transfer error")
added a call to regcache_drop_region() to error path in
_regmap_raw_write(). However that path runs with regmap lock taken,
and regcache_drop_region() tries to re-take it, causing deadlock:

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)

Fix that by calling map->cache_ops->drop() directly.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
---
 drivers/base/regmap/regmap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 25d26bb..e964d06 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -1475,7 +1475,11 @@ int _regmap_raw_write(struct regmap *map, unsigned int reg,
 
 		kfree(buf);
 	} else if (ret != 0 && !map->cache_bypass && map->format.parse_val) {
-		regcache_drop_region(map, reg, reg + 1);
+		/* regcache_drop_region() takes lock that we already have,
+		 * thus call map->cache_ops->drop() directly
+		 */
+		if (map->cache_ops && map->cache_ops->drop)
+			map->cache_ops->drop(map, reg, reg + 1);
 	}
 
 	trace_regmap_hw_write_done(map, reg, val_len / map->format.val_bytes);
-- 
2.1.4

Re: Regmap commit 815806e3 from 4.8-rc6 introduces a deadlock

[Mark Brown]

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On Thu, Sep 22, 2016 at 11:32:33AM +0300, Nikita Yushchenko wrote:
> Hi.
> 
> Here is a trace:

Please don't send cover letters for single patches, if there is anything
that needs saying put it in the changelog of the patch or after the ---
if it's administrative stuff.  This reduces mail volume and ensures that 
any important information is recorded in the changelog rather than being
lost. 

[-- Attachment #2: signature.asc --]
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Re: Regmap commit 815806e3 from 4.8-rc6 introduces a deadlock

[Nikita Yushchenko]

>> Hi.
>>
>> Here is a trace:
> 
> Please don't send cover letters for single patches, if there is anything
> that needs saying put it in the changelog of the patch or after the ---
> if it's administrative stuff.  This reduces mail volume and ensures that 
> any important information is recorded in the changelog rather than being
> lost. 

Ok.

Actually I first wrote the bug report and only then decided to send fix
as well :)

Nikita

Applied "regmap: fix deadlock on _regmap_raw_write() error path" to the regmap tree

[Mark Brown]

The patch

   regmap: fix deadlock on _regmap_raw_write() error path

has been applied to the regmap tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From f0aa1ce6259eb65f53f969b3250c1d0aac84f30b Mon Sep 17 00:00:00 2001
From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Date: Thu, 22 Sep 2016 12:02:25 +0300
Subject: [PATCH] regmap: fix deadlock on _regmap_raw_write() error path

Commit 815806e39bf6 ("regmap: drop cache if the bus transfer error")
added a call to regcache_drop_region() to error path in
_regmap_raw_write(). However that path runs with regmap lock taken,
and regcache_drop_region() tries to re-take it, causing a deadlock.
Fix that by calling map->cache_ops->drop() directly.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/base/regmap/regmap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 25d26bb18970..e964d068874d 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -1475,7 +1475,11 @@ int _regmap_raw_write(struct regmap *map, unsigned int reg,
 
 		kfree(buf);
 	} else if (ret != 0 && !map->cache_bypass && map->format.parse_val) {
-		regcache_drop_region(map, reg, reg + 1);
+		/* regcache_drop_region() takes lock that we already have,
+		 * thus call map->cache_ops->drop() directly
+		 */
+		if (map->cache_ops && map->cache_ops->drop)
+			map->cache_ops->drop(map, reg, reg + 1);
 	}
 
 	trace_regmap_hw_write_done(map, reg, val_len / map->format.val_bytes);
-- 
2.8.1