[PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[madhuparnabhowmik10]

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

This patch default enables CONFIG_PROVE_RCU_LIST option with
CONFIG_PROVE_RCU for RCU list lockdep debugging.

With this change, RCU list lockdep debugging will be default
enabled in CONFIG_PROVE_RCU=y kernels.

Most of the RCU users (in core kernel/, drivers/, and net/
subsystem) have already been modified to include lockdep
expressions hence RCU list debugging can be enabled by
default.

However, there are still chances of enountering
false-positive lockdep splats because not everything is converted,
in case RCU list primitives are used in non-RCU read-side critical
section but under the protection of a lock. It would be okay to
have a few false-positives, as long as bugs are identified, since this
patch only affects debugging kernels.

Co-developed-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 kernel/rcu/Kconfig.debug | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 4aa02eee8f6c..ec4bb6c09048 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -9,15 +9,10 @@ config PROVE_RCU
 	def_bool PROVE_LOCKING
 
 config PROVE_RCU_LIST
-	bool "RCU list lockdep debugging"
-	depends on PROVE_RCU && RCU_EXPERT
-	default n
+	def_bool PROVE_RCU
 	help
-	  Enable RCU lockdep checking for list usages. By default it is
-	  turned off since there are several list RCU users that still
-	  need to be converted to pass a lockdep expression. To prevent
-	  false-positive splats, we keep it default disabled but once all
-	  users are converted, we can remove this config option.
+	  Enable RCU lockdep checking for list usages. It is default
+	  enabled with CONFIG_PROVE_RCU.
 
 config TORTURE_TEST
 	tristate
-- 
2.17.1

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Joel Fernandes]

On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@gmail.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> This patch default enables CONFIG_PROVE_RCU_LIST option with
> CONFIG_PROVE_RCU for RCU list lockdep debugging.
> 
> With this change, RCU list lockdep debugging will be default
> enabled in CONFIG_PROVE_RCU=y kernels.
> 
> Most of the RCU users (in core kernel/, drivers/, and net/
> subsystem) have already been modified to include lockdep
> expressions hence RCU list debugging can be enabled by
> default.
> 
> However, there are still chances of enountering
> false-positive lockdep splats because not everything is converted,
> in case RCU list primitives are used in non-RCU read-side critical
> section but under the protection of a lock. It would be okay to
> have a few false-positives, as long as bugs are identified, since this
> patch only affects debugging kernels.
> 
> Co-developed-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>

thanks,

 - Joel

> ---
>  kernel/rcu/Kconfig.debug | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> index 4aa02eee8f6c..ec4bb6c09048 100644
> --- a/kernel/rcu/Kconfig.debug
> +++ b/kernel/rcu/Kconfig.debug
> @@ -9,15 +9,10 @@ config PROVE_RCU
>  	def_bool PROVE_LOCKING
>  
>  config PROVE_RCU_LIST
> -	bool "RCU list lockdep debugging"
> -	depends on PROVE_RCU && RCU_EXPERT
> -	default n
> +	def_bool PROVE_RCU
>  	help
> -	  Enable RCU lockdep checking for list usages. By default it is
> -	  turned off since there are several list RCU users that still
> -	  need to be converted to pass a lockdep expression. To prevent
> -	  false-positive splats, we keep it default disabled but once all
> -	  users are converted, we can remove this config option.
> +	  Enable RCU lockdep checking for list usages. It is default
> +	  enabled with CONFIG_PROVE_RCU.
>  
>  config TORTURE_TEST
>  	tristate
> -- 
> 2.17.1
> 

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Paul E. McKenney]

On Fri, Feb 28, 2020 at 09:21:22AM -0500, Joel Fernandes wrote:
> On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@gmail.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > 
> > This patch default enables CONFIG_PROVE_RCU_LIST option with
> > CONFIG_PROVE_RCU for RCU list lockdep debugging.
> > 
> > With this change, RCU list lockdep debugging will be default
> > enabled in CONFIG_PROVE_RCU=y kernels.
> > 
> > Most of the RCU users (in core kernel/, drivers/, and net/
> > subsystem) have already been modified to include lockdep
> > expressions hence RCU list debugging can be enabled by
> > default.
> > 
> > However, there are still chances of enountering
> > false-positive lockdep splats because not everything is converted,
> > in case RCU list primitives are used in non-RCU read-side critical
> > section but under the protection of a lock. It would be okay to
> > have a few false-positives, as long as bugs are identified, since this
> > patch only affects debugging kernels.
> > 
> > Co-developed-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Queued, thank you both!

							Thanx, Paul

> thanks,
> 
>  - Joel
> 
> > ---
> >  kernel/rcu/Kconfig.debug | 11 +++--------
> >  1 file changed, 3 insertions(+), 8 deletions(-)
> > 
> > diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> > index 4aa02eee8f6c..ec4bb6c09048 100644
> > --- a/kernel/rcu/Kconfig.debug
> > +++ b/kernel/rcu/Kconfig.debug
> > @@ -9,15 +9,10 @@ config PROVE_RCU
> >  	def_bool PROVE_LOCKING
> >  
> >  config PROVE_RCU_LIST
> > -	bool "RCU list lockdep debugging"
> > -	depends on PROVE_RCU && RCU_EXPERT
> > -	default n
> > +	def_bool PROVE_RCU
> >  	help
> > -	  Enable RCU lockdep checking for list usages. By default it is
> > -	  turned off since there are several list RCU users that still
> > -	  need to be converted to pass a lockdep expression. To prevent
> > -	  false-positive splats, we keep it default disabled but once all
> > -	  users are converted, we can remove this config option.
> > +	  Enable RCU lockdep checking for list usages. It is default
> > +	  enabled with CONFIG_PROVE_RCU.
> >  
> >  config TORTURE_TEST
> >  	tristate
> > -- 
> > 2.17.1
> > 

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Marek Szyprowski]

Dear All,

On 28.02.2020 10:24, madhuparnabhowmik10@gmail.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
>
> This patch default enables CONFIG_PROVE_RCU_LIST option with
> CONFIG_PROVE_RCU for RCU list lockdep debugging.
>
> With this change, RCU list lockdep debugging will be default
> enabled in CONFIG_PROVE_RCU=y kernels.
>
> Most of the RCU users (in core kernel/, drivers/, and net/
> subsystem) have already been modified to include lockdep
> expressions hence RCU list debugging can be enabled by
> default.
>
> However, there are still chances of enountering
> false-positive lockdep splats because not everything is converted,
> in case RCU list primitives are used in non-RCU read-side critical
> section but under the protection of a lock. It would be okay to
> have a few false-positives, as long as bugs are identified, since this
> patch only affects debugging kernels.
>
> Co-developed-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

This patch landed in today's linux-next (20200305) as commit 
c9af03c14bfdfd21515e556c3a90ffe2aadc964d. It causes the following kernel 
warning during system suspend/resume cycle on all ARM 32bit Samsung 
Exynos-based boards (kernel compiled from exynos_defconfig):

# rtcwake -s 10 -m mem
rtcwake: wakeup from "mem" using /dev/rtc0 at Sat Jan  1 00:01:13 2000
PM: suspend entry (deep)
Filesystems sync: 0.008 seconds
Freezing user space processes ... (elapsed 0.003 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.013 seconds) done.
printk: Suspending console(s) (use no_console_suspend to debug)

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/main.c:326 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: c1285d98 (device_links_srcu){....}, at: 
device_links_read_lock+0x0/0x50

stack backtrace:
CPU: 7 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c061ea2c>] 
(dpm_wait_for_subordinate+0xf4/0xfc)
[<c061ea2c>] (dpm_wait_for_subordinate) from [<c061f578>] 
(__device_suspend+0x20/0x838)
[<c061f578>] (__device_suspend) from [<c0622e1c>] (dpm_suspend+0x188/0x57c)
[<c0622e1c>] (dpm_suspend) from [<c0623bfc>] (dpm_suspend_start+0x98/0xa0)
[<c0623bfc>] (dpm_suspend_start) from [<c0197e20>] 
(suspend_devices_and_enter+0xec/0xc74)
[<c0197e20>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/main.c:1698 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
6 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: ebecd984 (&dev->mutex){....}, at: __device_suspend+0xf8/0x838
  #5: c1285d98 (device_links_srcu){....}, at: 
device_links_read_lock+0x0/0x50

stack backtrace:
CPU: 7 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c061f8bc>] (__device_suspend+0x364/0x838)
[<c061f8bc>] (__device_suspend) from [<c0622e1c>] (dpm_suspend+0x188/0x57c)
[<c0622e1c>] (dpm_suspend) from [<c0623bfc>] (dpm_suspend_start+0x98/0xa0)
[<c0623bfc>] (dpm_suspend_start) from [<c0197e20>] 
(suspend_devices_and_enter+0xec/0xc74)
[<c0197e20>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634
wake enabled for irq 160
wake enabled for irq 164
samsung-pinctrl 13400000.pinctrl: Setting external wakeup interrupt 
mask: 0xffffffe7

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/wakeup.c:408 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: c128722c (wakeup_srcu){....}, at: 
device_wakeup_arm_wake_irqs+0x0/0x124

stack backtrace:
CPU: 5 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c0625740>] 
(device_wakeup_arm_wake_irqs+0xdc/0x124)
[<c0625740>] (device_wakeup_arm_wake_irqs) from [<c0622120>] 
(dpm_suspend_noirq+0x1c/0x5a0)
[<c0622120>] (dpm_suspend_noirq) from [<c019805c>] 
(suspend_devices_and_enter+0x328/0xc74)
[<c019805c>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/main.c:1238 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: c1285d98 (device_links_srcu){....}, at: 
device_links_read_lock+0x0/0x50

stack backtrace:
CPU: 5 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c06202d4>] 
(__device_suspend_noirq+0x234/0x304)
[<c06202d4>] (__device_suspend_noirq) from [<c0622284>] 
(dpm_suspend_noirq+0x180/0x5a0)
[<c0622284>] (dpm_suspend_noirq) from [<c019805c>] 
(suspend_devices_and_enter+0x328/0xc74)
[<c019805c>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634
Disabling non-boot CPUs ...
IRQ 51: no longer affine to CPU1
IRQ 52: no longer affine to CPU2
IRQ 53: no longer affine to CPU3
IRQ 54: no longer affine to CPU4
IRQ 55: no longer affine to CPU5
IRQ 56: no longer affine to CPU6
IRQ 57: no longer affine to CPU7
Enabling non-boot CPUs ...
CPU1 is up
CPU2 is up
CPU3 is up
CPU4: detected I-Cache line size mismatch, workaround enabled
CPU4 is up
CPU5: detected I-Cache line size mismatch, workaround enabled
CPU5 is up
CPU6: detected I-Cache line size mismatch, workaround enabled
CPU6 is up
CPU7: detected I-Cache line size mismatch, workaround enabled
CPU7 is up

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/main.c:269 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: c1285d98 (device_links_srcu){....}, at: 
device_links_read_lock+0x0/0x50

stack backtrace:
CPU: 0 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c061ebf0>] 
(dpm_wait_for_superior+0x114/0x12c)
[<c061ebf0>] (dpm_wait_for_superior) from [<c061fe98>] 
(device_resume_noirq+0x74/0x238)
[<c061fe98>] (device_resume_noirq) from [<c0620a34>] 
(dpm_resume_noirq+0x160/0x53c)
[<c0620a34>] (dpm_resume_noirq) from [<c01983c8>] 
(suspend_devices_and_enter+0x694/0xc74)
[<c01983c8>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634
s3c-i2c 12c80000.i2c: slave address 0x00
s3c-i2c 12c80000.i2c: bus frequency set to 65 KHz

=============================
WARNING: suspicious RCU usage
5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
-----------------------------
drivers/base/power/wakeup.c:424 RCU-list traversed in non-reader section!!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by rtcwake/1452:
  #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
  #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
  #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
  #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
  #4: c128722c (wakeup_srcu){....}, at: 
device_wakeup_disarm_wake_irqs+0x0/0x124

stack backtrace:
CPU: 0 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
#7728
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
[<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
[<c0b5c50c>] (dump_stack) from [<c0625864>] 
(device_wakeup_disarm_wake_irqs+0xdc/0x124)
[<c0625864>] (device_wakeup_disarm_wake_irqs) from [<c0620b84>] 
(dpm_resume_noirq+0x2b0/0x53c)
[<c0620b84>] (dpm_resume_noirq) from [<c01983c8>] 
(suspend_devices_and_enter+0x694/0xc74)
[<c01983c8>] (suspend_devices_and_enter) from [<c0198da0>] 
(pm_suspend+0x3f8/0x480)
[<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
[<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
[<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
[<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
[<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
[<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeac89fa8 to 0xeac89ff0)
9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
00000000
9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
00028160
9fe0: 0000006c be980ac8 b6eae000 b6f0b634

I can help debugging this issue.

> ---
>   kernel/rcu/Kconfig.debug | 11 +++--------
>   1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> index 4aa02eee8f6c..ec4bb6c09048 100644
> --- a/kernel/rcu/Kconfig.debug
> +++ b/kernel/rcu/Kconfig.debug
> @@ -9,15 +9,10 @@ config PROVE_RCU
>   	def_bool PROVE_LOCKING
>   
>   config PROVE_RCU_LIST
> -	bool "RCU list lockdep debugging"
> -	depends on PROVE_RCU && RCU_EXPERT
> -	default n
> +	def_bool PROVE_RCU
>   	help
> -	  Enable RCU lockdep checking for list usages. By default it is
> -	  turned off since there are several list RCU users that still
> -	  need to be converted to pass a lockdep expression. To prevent
> -	  false-positive splats, we keep it default disabled but once all
> -	  users are converted, we can remove this config option.
> +	  Enable RCU lockdep checking for list usages. It is default
> +	  enabled with CONFIG_PROVE_RCU.
>   
>   config TORTURE_TEST
>   	tristate

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Madhuparna Bhowmik]

On Thu, Mar 05, 2020 at 11:50:37AM +0100, Marek Szyprowski wrote:
> Dear All,
> 
> On 28.02.2020 10:24, madhuparnabhowmik10@gmail.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> >
> > This patch default enables CONFIG_PROVE_RCU_LIST option with
> > CONFIG_PROVE_RCU for RCU list lockdep debugging.
> >
> > With this change, RCU list lockdep debugging will be default
> > enabled in CONFIG_PROVE_RCU=y kernels.
> >
> > Most of the RCU users (in core kernel/, drivers/, and net/
> > subsystem) have already been modified to include lockdep
> > expressions hence RCU list debugging can be enabled by
> > default.
> >
> > However, there are still chances of enountering
> > false-positive lockdep splats because not everything is converted,
> > in case RCU list primitives are used in non-RCU read-side critical
> > section but under the protection of a lock. It would be okay to
> > have a few false-positives, as long as bugs are identified, since this
> > patch only affects debugging kernels.
> >
> > Co-developed-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> This patch landed in today's linux-next (20200305) as commit 
> c9af03c14bfdfd21515e556c3a90ffe2aadc964d. It causes the following kernel 
> warning during system suspend/resume cycle on all ARM 32bit Samsung 
> Exynos-based boards (kernel compiled from exynos_defconfig):
> 
> # rtcwake -s 10 -m mem
> rtcwake: wakeup from "mem" using /dev/rtc0 at Sat Jan  1 00:01:13 2000
> PM: suspend entry (deep)
> Filesystems sync: 0.008 seconds
> Freezing user space processes ... (elapsed 0.003 seconds) done.
> OOM killer disabled.
> Freezing remaining freezable tasks ... (elapsed 0.013 seconds) done.
> printk: Suspending console(s) (use no_console_suspend to debug)
>
Hi,

These warnings in power/main.c and power/wakeup.c  are already
addressed.
Check this https://lore.kernel.org/patchwork/patch/1204515/
Thank you,
Madhuparna
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/main.c:326 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: c1285d98 (device_links_srcu){....}, at: 
> device_links_read_lock+0x0/0x50
> 
> stack backtrace:
> CPU: 7 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c061ea2c>] 
> (dpm_wait_for_subordinate+0xf4/0xfc)
> [<c061ea2c>] (dpm_wait_for_subordinate) from [<c061f578>] 
> (__device_suspend+0x20/0x838)
> [<c061f578>] (__device_suspend) from [<c0622e1c>] (dpm_suspend+0x188/0x57c)
> [<c0622e1c>] (dpm_suspend) from [<c0623bfc>] (dpm_suspend_start+0x98/0xa0)
> [<c0623bfc>] (dpm_suspend_start) from [<c0197e20>] 
> (suspend_devices_and_enter+0xec/0xc74)
> [<c0197e20>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> 
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/main.c:1698 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 6 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: ebecd984 (&dev->mutex){....}, at: __device_suspend+0xf8/0x838
>   #5: c1285d98 (device_links_srcu){....}, at: 
> device_links_read_lock+0x0/0x50
> 
> stack backtrace:
> CPU: 7 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c061f8bc>] (__device_suspend+0x364/0x838)
> [<c061f8bc>] (__device_suspend) from [<c0622e1c>] (dpm_suspend+0x188/0x57c)
> [<c0622e1c>] (dpm_suspend) from [<c0623bfc>] (dpm_suspend_start+0x98/0xa0)
> [<c0623bfc>] (dpm_suspend_start) from [<c0197e20>] 
> (suspend_devices_and_enter+0xec/0xc74)
> [<c0197e20>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> wake enabled for irq 160
> wake enabled for irq 164
> samsung-pinctrl 13400000.pinctrl: Setting external wakeup interrupt 
> mask: 0xffffffe7
> 
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/wakeup.c:408 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: c128722c (wakeup_srcu){....}, at: 
> device_wakeup_arm_wake_irqs+0x0/0x124
> 
> stack backtrace:
> CPU: 5 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c0625740>] 
> (device_wakeup_arm_wake_irqs+0xdc/0x124)
> [<c0625740>] (device_wakeup_arm_wake_irqs) from [<c0622120>] 
> (dpm_suspend_noirq+0x1c/0x5a0)
> [<c0622120>] (dpm_suspend_noirq) from [<c019805c>] 
> (suspend_devices_and_enter+0x328/0xc74)
> [<c019805c>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> 
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/main.c:1238 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: c1285d98 (device_links_srcu){....}, at: 
> device_links_read_lock+0x0/0x50
> 
> stack backtrace:
> CPU: 5 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c06202d4>] 
> (__device_suspend_noirq+0x234/0x304)
> [<c06202d4>] (__device_suspend_noirq) from [<c0622284>] 
> (dpm_suspend_noirq+0x180/0x5a0)
> [<c0622284>] (dpm_suspend_noirq) from [<c019805c>] 
> (suspend_devices_and_enter+0x328/0xc74)
> [<c019805c>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> Disabling non-boot CPUs ...
> IRQ 51: no longer affine to CPU1
> IRQ 52: no longer affine to CPU2
> IRQ 53: no longer affine to CPU3
> IRQ 54: no longer affine to CPU4
> IRQ 55: no longer affine to CPU5
> IRQ 56: no longer affine to CPU6
> IRQ 57: no longer affine to CPU7
> Enabling non-boot CPUs ...
> CPU1 is up
> CPU2 is up
> CPU3 is up
> CPU4: detected I-Cache line size mismatch, workaround enabled
> CPU4 is up
> CPU5: detected I-Cache line size mismatch, workaround enabled
> CPU5 is up
> CPU6: detected I-Cache line size mismatch, workaround enabled
> CPU6 is up
> CPU7: detected I-Cache line size mismatch, workaround enabled
> CPU7 is up
> 
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/main.c:269 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: c1285d98 (device_links_srcu){....}, at: 
> device_links_read_lock+0x0/0x50
> 
> stack backtrace:
> CPU: 0 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c061ebf0>] 
> (dpm_wait_for_superior+0x114/0x12c)
> [<c061ebf0>] (dpm_wait_for_superior) from [<c061fe98>] 
> (device_resume_noirq+0x74/0x238)
> [<c061fe98>] (device_resume_noirq) from [<c0620a34>] 
> (dpm_resume_noirq+0x160/0x53c)
> [<c0620a34>] (dpm_resume_noirq) from [<c01983c8>] 
> (suspend_devices_and_enter+0x694/0xc74)
> [<c01983c8>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> s3c-i2c 12c80000.i2c: slave address 0x00
> s3c-i2c 12c80000.i2c: bus frequency set to 65 KHz
> 
> =============================
> WARNING: suspicious RCU usage
> 5.6.0-rc1-00177-gc9af03c14bfd #7728 Not tainted
> -----------------------------
> drivers/base/power/wakeup.c:424 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/1452:
>   #0: edba7270 (sb_writers#7){.+.+}, at: vfs_write+0x16c/0x180
>   #1: ece71f44 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd0/0x228
>   #2: eda72008 (kn->count#98){.+.+}, at: kernfs_fop_write+0xd8/0x228
>   #3: c121223c (system_transition_mutex){+.+.}, at: pm_suspend+0xc0/0x480
>   #4: c128722c (wakeup_srcu){....}, at: 
> device_wakeup_disarm_wake_irqs+0x0/0x124
> 
> stack backtrace:
> CPU: 0 PID: 1452 Comm: rtcwake Not tainted 5.6.0-rc1-00177-gc9af03c14bfd 
> #7728
> Hardware name: Samsung Exynos (Flattened Device Tree)
> [<c0112710>] (unwind_backtrace) from [<c010e1f4>] (show_stack+0x10/0x14)
> [<c010e1f4>] (show_stack) from [<c0b5c50c>] (dump_stack+0xb4/0xe0)
> [<c0b5c50c>] (dump_stack) from [<c0625864>] 
> (device_wakeup_disarm_wake_irqs+0xdc/0x124)
> [<c0625864>] (device_wakeup_disarm_wake_irqs) from [<c0620b84>] 
> (dpm_resume_noirq+0x2b0/0x53c)
> [<c0620b84>] (dpm_resume_noirq) from [<c01983c8>] 
> (suspend_devices_and_enter+0x694/0xc74)
> [<c01983c8>] (suspend_devices_and_enter) from [<c0198da0>] 
> (pm_suspend+0x3f8/0x480)
> [<c0198da0>] (pm_suspend) from [<c019696c>] (state_store+0x6c/0xc8)
> [<c019696c>] (state_store) from [<c0356c78>] (kernfs_fop_write+0x10c/0x228)
> [<c0356c78>] (kernfs_fop_write) from [<c02b52c8>] (__vfs_write+0x30/0x1d0)
> [<c02b52c8>] (__vfs_write) from [<c02b8264>] (vfs_write+0xa4/0x180)
> [<c02b8264>] (vfs_write) from [<c02b84c0>] (ksys_write+0x60/0xd8)
> [<c02b84c0>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
> Exception stack(0xeac89fa8 to 0xeac89ff0)
> 9fa0:                   00000004 0002b440 00000004 0002b440 00000004 
> 00000000
> 9fc0: 00000004 0002b440 000291b0 00000004 0002b440 00000004 be980bfc 
> 00028160
> 9fe0: 0000006c be980ac8 b6eae000 b6f0b634
> 
> I can help debugging this issue.
> 
> > ---
> >   kernel/rcu/Kconfig.debug | 11 +++--------
> >   1 file changed, 3 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> > index 4aa02eee8f6c..ec4bb6c09048 100644
> > --- a/kernel/rcu/Kconfig.debug
> > +++ b/kernel/rcu/Kconfig.debug
> > @@ -9,15 +9,10 @@ config PROVE_RCU
> >   	def_bool PROVE_LOCKING
> >   
> >   config PROVE_RCU_LIST
> > -	bool "RCU list lockdep debugging"
> > -	depends on PROVE_RCU && RCU_EXPERT
> > -	default n
> > +	def_bool PROVE_RCU
> >   	help
> > -	  Enable RCU lockdep checking for list usages. By default it is
> > -	  turned off since there are several list RCU users that still
> > -	  need to be converted to pass a lockdep expression. To prevent
> > -	  false-positive splats, we keep it default disabled but once all
> > -	  users are converted, we can remove this config option.
> > +	  Enable RCU lockdep checking for list usages. It is default
> > +	  enabled with CONFIG_PROVE_RCU.
> >   
> >   config TORTURE_TEST
> >   	tristate
> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Guenter Roeck]

On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@gmail.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> This patch default enables CONFIG_PROVE_RCU_LIST option with
> CONFIG_PROVE_RCU for RCU list lockdep debugging.
> 
> With this change, RCU list lockdep debugging will be default
> enabled in CONFIG_PROVE_RCU=y kernels.
> 
> Most of the RCU users (in core kernel/, drivers/, and net/
> subsystem) have already been modified to include lockdep
> expressions hence RCU list debugging can be enabled by
> default.
> 
> However, there are still chances of enountering
> false-positive lockdep splats because not everything is converted,
> in case RCU list primitives are used in non-RCU read-side critical
> section but under the protection of a lock. It would be okay to
> have a few false-positives, as long as bugs are identified, since this
> patch only affects debugging kernels.
> 
> Co-developed-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

Who is going to fix the fallout ?

fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!!
kernel/kprobes.c:329 RCU-list traversed in non-reader section!!
net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

This is just from my boot tests. I'll keep PROVE_RCU enabled for the
time being, but unless the noise is addressed I'll have to disable it
because otherwise the real problems disappear in the noise.

Guenter

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Madhuparna Bhowmik]

On Thu, Mar 05, 2020 at 07:52:38AM -0800, Guenter Roeck wrote:
> On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@gmail.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > 
> > This patch default enables CONFIG_PROVE_RCU_LIST option with
> > CONFIG_PROVE_RCU for RCU list lockdep debugging.
> > 
> > With this change, RCU list lockdep debugging will be default
> > enabled in CONFIG_PROVE_RCU=y kernels.
> > 
> > Most of the RCU users (in core kernel/, drivers/, and net/
> > subsystem) have already been modified to include lockdep
> > expressions hence RCU list debugging can be enabled by
> > default.
> > 
> > However, there are still chances of enountering
> > false-positive lockdep splats because not everything is converted,
> > in case RCU list primitives are used in non-RCU read-side critical
> > section but under the protection of a lock. It would be okay to
> > have a few false-positives, as long as bugs are identified, since this
> > patch only affects debugging kernels.
> > 
> > Co-developed-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> Who is going to fix the fallout ?
> 
> fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!!
> kernel/kprobes.c:329 RCU-list traversed in non-reader section!!
> net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
>
Hi,
There is already a patch for fixing the warnings in kernel/kprobes.c :
https://lore.kernel.org/lkml/157905963533.2268.4672153983131918123.stgit@devnote2/

Same for net/ipv4/ipmr:
https://lore.kernel.org/patchwork/patch/1198934/

Can you please send the warning with the stack backtrace and locks held
for btrfs/block-group.c, I will work on it.

Thank you,
Madhuparna
> This is just from my boot tests. I'll keep PROVE_RCU enabled for the
> time being, but unless the noise is addressed I'll have to disable it
> because otherwise the real problems disappear in the noise.
> 
> Guenter

Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Guenter Roeck]

On Thu, Mar 05, 2020 at 11:09:54PM +0530, Madhuparna Bhowmik wrote:
> On Thu, Mar 05, 2020 at 07:52:38AM -0800, Guenter Roeck wrote:
> > On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@gmail.com wrote:
> > > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > > 
> > > This patch default enables CONFIG_PROVE_RCU_LIST option with
> > > CONFIG_PROVE_RCU for RCU list lockdep debugging.
> > > 
> > > With this change, RCU list lockdep debugging will be default
> > > enabled in CONFIG_PROVE_RCU=y kernels.
> > > 
> > > Most of the RCU users (in core kernel/, drivers/, and net/
> > > subsystem) have already been modified to include lockdep
> > > expressions hence RCU list debugging can be enabled by
> > > default.
> > > 
> > > However, there are still chances of enountering
> > > false-positive lockdep splats because not everything is converted,
> > > in case RCU list primitives are used in non-RCU read-side critical
> > > section but under the protection of a lock. It would be okay to
> > > have a few false-positives, as long as bugs are identified, since this
> > > patch only affects debugging kernels.
> > > 
> > > Co-developed-by: Amol Grover <frextrite@gmail.com>
> > > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > 
> > Who is going to fix the fallout ?
> > 
> > fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!!
> > kernel/kprobes.c:329 RCU-list traversed in non-reader section!!
> > net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> >
> Hi,
> There is already a patch for fixing the warnings in kernel/kprobes.c :
> https://lore.kernel.org/lkml/157905963533.2268.4672153983131918123.stgit@devnote2/
> 
> Same for net/ipv4/ipmr:
> https://lore.kernel.org/patchwork/patch/1198934/
> 
> Can you please send the warning with the stack backtrace and locks held
> for btrfs/block-group.c, I will work on it.
> 

See below. I think that should be easy to reproduce by mounting
a btrfs file system.

Guenter

---
[   28.920119] BTRFS: device fsid afe7540f-98fe-4a5c-ba94-3fb85a5da345 devid 1 transid 6 /dev/root scanned by swapper/0 (1)
[   28.961347] BTRFS info (device sda): disk space caching is enabled
[   28.963199] BTRFS info (device sda): has skinny extents
[   28.963427] BTRFS info (device sda): flagging fs with big metadata feature
[   29.104392]
[   29.104591] =============================
[   29.104756] WARNING: suspicious RCU usage
[   29.105046] 5.6.0-rc4-next-20200305 #1 Not tainted
[   29.105231] -----------------------------
[   29.105401] fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!!
[   29.105643]
[   29.105643] other info that might help us debug this:
[   29.105643]
[   29.106344]
[   29.106344] rcu_scheduler_active = 2, debug_locks = 1
[   29.106590] 1 lock held by swapper/0/1:
[   29.106776]  #0: ffff0000199e90d8 (&type->s_umount_key#23/1){+.+.}, at: alloc_super+0xac/0x2c0
[   29.107436]
[   29.107436] stack backtrace:
[   29.107784] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-20200305 #1
[   29.107989] Hardware name: linux,dummy-virt (DT)
[   29.108344] Call trace:
[   29.108488]  dump_backtrace+0x0/0x1a0
[   29.108638]  show_stack+0x14/0x20
[   29.108784]  dump_stack+0xe8/0x150
[   29.108921]  lockdep_rcu_suspicious+0xf8/0x108
[   29.109071]  btrfs_read_block_groups+0x754/0x860
[   29.109222]  open_ctree+0xe74/0x1580
[   29.109359]  btrfs_mount_root+0x3cc/0x4c0
[   29.109514]  legacy_get_tree+0x2c/0x60
[   29.109653]  vfs_get_tree+0x24/0xe8
[   29.109872]  fc_mount+0x14/0x50
[   29.110010]  vfs_kern_mount.part.41+0x68/0x98
[   29.110158]  vfs_kern_mount+0x10/0x20
[   29.110297]  btrfs_mount+0x158/0x4b0
[   29.110434]  legacy_get_tree+0x2c/0x60
[   29.110573]  vfs_get_tree+0x24/0xe8
[   29.110709]  do_mount+0x568/0x998
[   29.110849]  do_mount_root+0x8c/0x11c
[   29.110990]  mount_block_root+0x114/0x244
[   29.111134]  mount_root+0x124/0x154
[   29.111272]  prepare_namespace+0x128/0x164
[   29.111417]  kernel_init_freeable+0x298/0x2b8
[   29.111569]  kernel_init+0x10/0x100
[   29.111710]  ret_from_fork+0x10/0x18