[PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[Anders Roxell]

When the test 'CONFIG_DEBUG_TEST_DRIVER_REMOVE=y' is enabled,
arch_initcall(pl011_init) came before subsys_initcall(default_bdi_init).
devtmpfs gets killed because we try to remove a file and decrement the
wb reference count before the noop_backing_device_info gets initialized.

[    0.332075] Serial: AMBA PL011 UART driver
[    0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1
[    0.502382] console [ttyAMA0] enabled
[    0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000
[    0.516053] Mem abort info:
[    0.516222]   ESR = 0x96000004
[    0.516417]   Exception class = DABT (current EL), IL = 32 bits
[    0.516641]   SET = 0, FnV = 0
[    0.516826]   EA = 0, S1PTW = 0
[    0.516984] Data abort info:
[    0.517149]   ISV = 0, ISS = 0x00000004
[    0.517339]   CM = 0, WnR = 0
[    0.517553] [0000800074c12000] user address but active_mm is swapper
[    0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[    0.518305] Modules linked in:
[    0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82
[    0.519307] Hardware name: linux,dummy-virt (DT)
[    0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO)
[    0.519959] pc : __destroy_inode+0x94/0x2a8
[    0.520212] lr : __destroy_inode+0x78/0x2a8
[    0.520401] sp : ffff0000098c3b20
[    0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714
[    0.520904] x27: 0000000000002000 x26: 0000000000002000
[    0.521179] x25: ffff000009583000 x24: 0000000000000000
[    0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0
[    0.521737] x21: ffff0000093f9338 x20: 0000000000000000
[    0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400
[    0.522376] x17: 0000000000000000 x16: 0000000000000000
[    0.522727] x15: 0000000000000400 x14: 0000000000000400
[    0.523068] x13: 0000000000000001 x12: 0000000000000001
[    0.523421] x11: 0000000000000000 x10: 0000000000000970
[    0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190
[    0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88
[    0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb
[    0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff
[    0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000
[    0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____))
[    0.525529] Call trace:
[    0.525806]  __destroy_inode+0x94/0x2a8
[    0.526108]  destroy_inode+0x34/0x88
[    0.526370]  evict+0x144/0x1c8
[    0.526636]  iput+0x184/0x230
[    0.526871]  dentry_unlink_inode+0x118/0x130
[    0.527152]  d_delete+0xd8/0xe0
[    0.527420]  vfs_unlink+0x240/0x270
[    0.527665]  handle_remove+0x1d8/0x330
[    0.527875]  devtmpfsd+0x138/0x1c8
[    0.528085]  kthread+0x14c/0x158
[    0.528291]  ret_from_fork+0x10/0x18
[    0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04)
[    0.529367] ---[ end trace 5a3dee47727f877c ]---

Rework to set suppress_bind_attrs flag to avoid removing the device when
CONFIG_DEBUG_TEST_DRIVER_REMOVE=y. This applies for pic32_uart and
xilinx_uartps as well.

Cc: Arnd Bergmann <arnd@arndb.de>
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
 drivers/tty/serial/amba-pl011.c    | 2 ++
 drivers/tty/serial/pic32_uart.c    | 1 +
 drivers/tty/serial/xilinx_uartps.c | 1 +
 3 files changed, 4 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index ebd33c0232e6..89ade213a1a9 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2780,6 +2780,7 @@ static struct platform_driver arm_sbsa_uart_platform_driver = {
 		.name	= "sbsa-uart",
 		.of_match_table = of_match_ptr(sbsa_uart_of_match),
 		.acpi_match_table = ACPI_PTR(sbsa_uart_acpi_match),
+		.suppress_bind_attrs = IS_BUILTIN(CONFIG_SERIAL_AMBA_PL011),
 	},
 };
 
@@ -2808,6 +2809,7 @@ static struct amba_driver pl011_driver = {
 	.drv = {
 		.name	= "uart-pl011",
 		.pm	= &pl011_dev_pm_ops,
+		.suppress_bind_attrs = IS_BUILTIN(CONFIG_SERIAL_AMBA_PL011),
 	},
 	.id_table	= pl011_ids,
 	.probe		= pl011_probe,
diff --git a/drivers/tty/serial/pic32_uart.c b/drivers/tty/serial/pic32_uart.c
index fd80d999308d..0bdf1687983f 100644
--- a/drivers/tty/serial/pic32_uart.c
+++ b/drivers/tty/serial/pic32_uart.c
@@ -919,6 +919,7 @@ static struct platform_driver pic32_uart_platform_driver = {
 	.driver		= {
 		.name	= PIC32_DEV_NAME,
 		.of_match_table	= of_match_ptr(pic32_serial_dt_ids),
+		.suppress_bind_attrs = IS_BUILTIN(CONFIG_SERIAL_PIC32),
 	},
 };
 
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 0e3dae461f71..806a953ac8d4 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1717,6 +1717,7 @@ static struct platform_driver cdns_uart_platform_driver = {
 		.name = CDNS_UART_NAME,
 		.of_match_table = cdns_uart_of_match,
 		.pm = &cdns_uart_dev_pm_ops,
+		.suppress_bind_attrs = IS_BUILTIN(CONFIG_SERIAL_XILINX_PS_UART),
 		},
 };
 
-- 
2.19.1

[PATCH 2/2] writeback: don't decrement wb->refcnt if !wb->bdi

[Anders Roxell]

When enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE devtmpfs gets killed
because we try to remove a file and decrement the wb reference count
before the noop_backing_device_info gets initialized.

Since arch_initcall(pl011_init) came before
subsys_initcall(default_bdi_init), devtmpfs' handle_remove() crashes
because the reference count is a NULL pointer only because bdi->wb
hasn't been initialized yet.

[    0.332075] Serial: AMBA PL011 UART driver
[    0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1
[    0.502382] console [ttyAMA0] enabled
[    0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000
[    0.516053] Mem abort info:
[    0.516222]   ESR = 0x96000004
[    0.516417]   Exception class = DABT (current EL), IL = 32 bits
[    0.516641]   SET = 0, FnV = 0
[    0.516826]   EA = 0, S1PTW = 0
[    0.516984] Data abort info:
[    0.517149]   ISV = 0, ISS = 0x00000004
[    0.517339]   CM = 0, WnR = 0
[    0.517553] [0000800074c12000] user address but active_mm is swapper
[    0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[    0.518305] Modules linked in:
[    0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82
[    0.519307] Hardware name: linux,dummy-virt (DT)
[    0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO)
[    0.519959] pc : __destroy_inode+0x94/0x2a8
[    0.520212] lr : __destroy_inode+0x78/0x2a8
[    0.520401] sp : ffff0000098c3b20
[    0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714
[    0.520904] x27: 0000000000002000 x26: 0000000000002000
[    0.521179] x25: ffff000009583000 x24: 0000000000000000
[    0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0
[    0.521737] x21: ffff0000093f9338 x20: 0000000000000000
[    0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400
[    0.522376] x17: 0000000000000000 x16: 0000000000000000
[    0.522727] x15: 0000000000000400 x14: 0000000000000400
[    0.523068] x13: 0000000000000001 x12: 0000000000000001
[    0.523421] x11: 0000000000000000 x10: 0000000000000970
[    0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190
[    0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88
[    0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb
[    0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff
[    0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000
[    0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____))
[    0.525529] Call trace:
[    0.525806]  __destroy_inode+0x94/0x2a8
[    0.526108]  destroy_inode+0x34/0x88
[    0.526370]  evict+0x144/0x1c8
[    0.526636]  iput+0x184/0x230
[    0.526871]  dentry_unlink_inode+0x118/0x130
[    0.527152]  d_delete+0xd8/0xe0
[    0.527420]  vfs_unlink+0x240/0x270
[    0.527665]  handle_remove+0x1d8/0x330
[    0.527875]  devtmpfsd+0x138/0x1c8
[    0.528085]  kthread+0x14c/0x158
[    0.528291]  ret_from_fork+0x10/0x18
[    0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04)
[    0.529367] ---[ end trace 5a3dee47727f877c ]---

Rework so that wb_put have an extra check if wb->bdi before decrement
wb->refcnt and also add a WARN_ON to get a warning if it happens again
in other drivers.

Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
Cc: Arnd Bergmann <arnd@arndb.de>
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
 include/linux/backing-dev-defs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 9a6bc0951cfa..20721550d32a 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -258,7 +258,7 @@ static inline void wb_get(struct bdi_writeback *wb)
  */
 static inline void wb_put(struct bdi_writeback *wb)
 {
-	if (wb != &wb->bdi->wb)
+	if (!WARN_ON(!wb->bdi) && wb != &wb->bdi->wb)
 		percpu_ref_put(&wb->refcnt);
 }
 
-- 
2.19.1

Re: [PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[Andrew Morton]

On Wed, 17 Oct 2018 16:03:10 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:

> Cc: Arnd Bergmann <arnd@arndb.de>
> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

This should have Arnd's Signed-off-by: as well.

Re: [PATCH 2/2] writeback: don't decrement wb->refcnt if !wb->bdi

[Andrew Morton]

On Wed, 17 Oct 2018 16:03:11 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:

> When enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE devtmpfs gets killed
> because we try to remove a file and decrement the wb reference count
> before the noop_backing_device_info gets initialized.
> 
> Since arch_initcall(pl011_init) came before
> subsys_initcall(default_bdi_init), devtmpfs' handle_remove() crashes
> because the reference count is a NULL pointer only because bdi->wb
> hasn't been initialized yet.

Is this changelog correct?  What does drivers/tty/serial/amba-pl011.c
have to do with page writeback?  Confused.

> [    0.332075] Serial: AMBA PL011 UART driver
> [    0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1
> [    0.502382] console [ttyAMA0] enabled
> [    0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000
> [    0.516053] Mem abort info:
> [    0.516222]   ESR = 0x96000004
> [    0.516417]   Exception class = DABT (current EL), IL = 32 bits
> [    0.516641]   SET = 0, FnV = 0
> [    0.516826]   EA = 0, S1PTW = 0
> [    0.516984] Data abort info:
> [    0.517149]   ISV = 0, ISS = 0x00000004
> [    0.517339]   CM = 0, WnR = 0
> [    0.517553] [0000800074c12000] user address but active_mm is swapper
> [    0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [    0.518305] Modules linked in:
> [    0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82
> [    0.519307] Hardware name: linux,dummy-virt (DT)
> [    0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO)
> [    0.519959] pc : __destroy_inode+0x94/0x2a8
> [    0.520212] lr : __destroy_inode+0x78/0x2a8
> [    0.520401] sp : ffff0000098c3b20
> [    0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714
> [    0.520904] x27: 0000000000002000 x26: 0000000000002000
> [    0.521179] x25: ffff000009583000 x24: 0000000000000000
> [    0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0
> [    0.521737] x21: ffff0000093f9338 x20: 0000000000000000
> [    0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400
> [    0.522376] x17: 0000000000000000 x16: 0000000000000000
> [    0.522727] x15: 0000000000000400 x14: 0000000000000400
> [    0.523068] x13: 0000000000000001 x12: 0000000000000001
> [    0.523421] x11: 0000000000000000 x10: 0000000000000970
> [    0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190
> [    0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88
> [    0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb
> [    0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff
> [    0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000
> [    0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____))
> [    0.525529] Call trace:
> [    0.525806]  __destroy_inode+0x94/0x2a8
> [    0.526108]  destroy_inode+0x34/0x88
> [    0.526370]  evict+0x144/0x1c8
> [    0.526636]  iput+0x184/0x230
> [    0.526871]  dentry_unlink_inode+0x118/0x130
> [    0.527152]  d_delete+0xd8/0xe0
> [    0.527420]  vfs_unlink+0x240/0x270
> [    0.527665]  handle_remove+0x1d8/0x330
> [    0.527875]  devtmpfsd+0x138/0x1c8
> [    0.528085]  kthread+0x14c/0x158
> [    0.528291]  ret_from_fork+0x10/0x18
> [    0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04)

Seems that there is indeed some form of linkage.  Can this be spelled
out more in the changelog please?

> 
> Rework so that wb_put have an extra check if wb->bdi before decrement
> wb->refcnt and also add a WARN_ON to get a warning if it happens again
> in other drivers.
> 
> Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
> Cc: Arnd Bergmann <arnd@arndb.de>
> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

Signed-off-by: Arnd, please.

> --- a/include/linux/backing-dev-defs.h
> +++ b/include/linux/backing-dev-defs.h
> @@ -258,7 +258,7 @@ static inline void wb_get(struct bdi_writeback *wb)
>   */
>  static inline void wb_put(struct bdi_writeback *wb)
>  {
> -	if (wb != &wb->bdi->wb)
> +	if (!WARN_ON(!wb->bdi) && wb != &wb->bdi->wb)
>  		percpu_ref_put(&wb->refcnt);
>  }

The !WARN_ON(!expr) isn't very easy to follow.   This:

{
	if (WARN_ON_ONCE(!wb->bdi)) {
		/*
		 * Nice comment explaining how this situation comes about
		 */
		return;
	}

	if (wb != &wb->bdi->wb)
		percpu_ref_put(&wb->refcnt);
}

is better, no?

Also, please note the s/WARN_ON/WARN_ON_ONCE/.  I don't think we gain
anything from reporting the same thing many times?

Re: [PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[Jeffrey Hugo]

On 10/17/2018 4:05 PM, Andrew Morton wrote:
> On Wed, 17 Oct 2018 16:03:10 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:
> 
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
>> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
> 
> This should have Arnd's Signed-off-by: as well.

I'm just interested to know, why?

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[Andrew Morton]

On Wed, 17 Oct 2018 16:21:08 -0600 Jeffrey Hugo <jhugo@codeaurora.org> wrote:

> On 10/17/2018 4:05 PM, Andrew Morton wrote:
> > On Wed, 17 Oct 2018 16:03:10 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:
> > 
> >> Cc: Arnd Bergmann <arnd@arndb.de>
> >> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
> >> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
> > 
> > This should have Arnd's Signed-off-by: as well.
> 
> I'm just interested to know, why?

So that Arnd certifies that

        (a) The contribution was created in whole or in part by me and I
            have the right to submit it under the open source license
            indicated in the file; or

and all the other stuff in Documentation/process/submitting-patches.rst
section 11!

Also, because section 12 says so :)  And that final sentence is, I
believe, appropriate.

Re: [PATCH 1/2] serial: set suppress_bind_attrs flag only if builtin

[Jeffrey Hugo]

On 10/17/2018 4:32 PM, Andrew Morton wrote:
> On Wed, 17 Oct 2018 16:21:08 -0600 Jeffrey Hugo <jhugo@codeaurora.org> wrote:
> 
>> On 10/17/2018 4:05 PM, Andrew Morton wrote:
>>> On Wed, 17 Oct 2018 16:03:10 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:
>>>
>>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>>> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
>>>> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
>>>
>>> This should have Arnd's Signed-off-by: as well.
>>
>> I'm just interested to know, why?
> 
> So that Arnd certifies that
> 
>          (a) The contribution was created in whole or in part by me and I
>              have the right to submit it under the open source license
>              indicated in the file; or
> 
> and all the other stuff in Documentation/process/submitting-patches.rst
> section 11!
> 
> Also, because section 12 says so :)  And that final sentence is, I
> believe, appropriate.

Ah, interesting.  I see that the documentation was updated since I was 
told last year in the same situation by a different maintainer that 
co-authors should not have SOB lines on the patch.

Good to know.  Thanks for illuminating me.

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.