At least trackpoint_disconnect wants to remove some sysfs files, and
we can't remove sysfs files while holding psmouse_mutex:
======================================================
WARNING: possible circular locking dependency detected
4.16.0-rc5-g613eb885b69e-drmtip_1+ #1 Tainted: G U
------------------------------------------------------
kworker/0:3/102 is trying to acquire lock:
(kn->count#130){++++}, at: [<000000009679748b>] kernfs_remove_by_name_ns+0x3b/0x80
but task is already holding lock:
(psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (psmouse_mutex){+.+.}:
psmouse_attr_set_helper+0x28/0x140
kernfs_fop_write+0xfe/0x180
__vfs_write+0x1e/0x130
vfs_write+0xbd/0x1b0
SyS_write+0x40/0xa0
do_syscall_64+0x65/0x1a0
entry_SYSCALL_64_after_hwframe+0x42/0xb7
-> #0 (kn->count#130){++++}:
__kernfs_remove+0x243/0x2b0
kernfs_remove_by_name_ns+0x3b/0x80
remove_files.isra.0+0x2b/0x60
sysfs_remove_group+0x38/0x80
sysfs_remove_groups+0x24/0x40
trackpoint_disconnect+0x2c/0x50
psmouse_disconnect+0x8f/0x160
serio_disconnect_driver+0x28/0x40
serio_driver_remove+0xc/0x10
device_release_driver_internal+0x15b/0x230
serio_handle_event+0x1c8/0x260
process_one_work+0x215/0x620
worker_thread+0x48/0x3a0
kthread+0xfb/0x130
ret_from_fork+0x3a/0x50
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(psmouse_mutex);
lock(kn->count#130);
lock(psmouse_mutex);
lock(kn->count#130);
*** DEADLOCK ***
6 locks held by kworker/0:3/102:
#0: ((wq_completion)"events_long"){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
#1: (serio_event_work){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
#2: (serio_mutex){+.+.}, at: [<00000000c8a49847>] serio_handle_event+0x23/0x260
#3: (&dev->mutex){....}, at: [<00000000b55eee75>] device_release_driver_internal+0x2f/0x230
#4: (&serio->drv_mutex){+.+.}, at: [<000000009719f997>] serio_disconnect_driver+0x16/0x40
#5: (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
stack backtrace:
CPU: 0 PID: 102 Comm: kworker/0:3 Tainted: G U 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1
Hardware name: LENOVO 74591P0/74591P0, BIOS 6DET28WW (1.05 ) 07/30/2008
Workqueue: events_long serio_handle_event
Call Trace:
dump_stack+0x5f/0x86
print_circular_bug.isra.18+0x1d0/0x2c0
__lock_acquire+0x14ae/0x1b60
? kernfs_remove_by_name_ns+0x20/0x80
? lock_acquire+0xaf/0x200
lock_acquire+0xaf/0x200
? kernfs_remove_by_name_ns+0x3b/0x80
__kernfs_remove+0x243/0x2b0
? kernfs_remove_by_name_ns+0x3b/0x80
? kernfs_name_hash+0xd/0x70
? kernfs_find_ns+0x7e/0x100
kernfs_remove_by_name_ns+0x3b/0x80
remove_files.isra.0+0x2b/0x60
sysfs_remove_group+0x38/0x80
sysfs_remove_groups+0x24/0x40
trackpoint_disconnect+0x2c/0x50
psmouse_disconnect+0x8f/0x160
serio_disconnect_driver+0x28/0x40
serio_driver_remove+0xc/0x10
device_release_driver_internal+0x15b/0x230
serio_handle_event+0x1c8/0x260
process_one_work+0x215/0x620
worker_thread+0x48/0x3a0
? _raw_spin_unlock_irqrestore+0x4c/0x60
kthread+0xfb/0x130
? process_one_work+0x620/0x620
? _kthread_create_on_node+0x30/0x30
ret_from_fork+0x3a/0x50
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Dmitry Torokhov <[email protected]>
Cc: Benjamin Tissoires <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Arvind Yadav <[email protected]>
Cc: Stephen Lyons <[email protected]>
Cc: [email protected]
---
drivers/input/mouse/psmouse-base.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
index 8900c3166ebf..06ccd8e22f3c 100644
--- a/drivers/input/mouse/psmouse-base.c
+++ b/drivers/input/mouse/psmouse-base.c
@@ -1484,8 +1484,10 @@ static void psmouse_disconnect(struct serio *serio)
psmouse_deactivate(parent);
}
+ mutex_unlock(&psmouse_mutex);
if (psmouse->disconnect)
psmouse->disconnect(psmouse);
+ mutex_lock(&psmouse_mutex);
if (parent && parent->pt_deactivate)
parent->pt_deactivate(parent);
--
2.17.0
Hi Daniel,
On Mon, Apr 30, 2018 at 09:56:49PM +0200, Daniel Vetter wrote:
> At least trackpoint_disconnect wants to remove some sysfs files, and
> we can't remove sysfs files while holding psmouse_mutex:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1 Tainted: G U
> ------------------------------------------------------
> kworker/0:3/102 is trying to acquire lock:
> (kn->count#130){++++}, at: [<000000009679748b>] kernfs_remove_by_name_ns+0x3b/0x80
>
> but task is already holding lock:
> (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (psmouse_mutex){+.+.}:
> psmouse_attr_set_helper+0x28/0x140
> kernfs_fop_write+0xfe/0x180
> __vfs_write+0x1e/0x130
> vfs_write+0xbd/0x1b0
> SyS_write+0x40/0xa0
> do_syscall_64+0x65/0x1a0
> entry_SYSCALL_64_after_hwframe+0x42/0xb7
>
> -> #0 (kn->count#130){++++}:
> __kernfs_remove+0x243/0x2b0
> kernfs_remove_by_name_ns+0x3b/0x80
> remove_files.isra.0+0x2b/0x60
> sysfs_remove_group+0x38/0x80
> sysfs_remove_groups+0x24/0x40
> trackpoint_disconnect+0x2c/0x50
> psmouse_disconnect+0x8f/0x160
> serio_disconnect_driver+0x28/0x40
> serio_driver_remove+0xc/0x10
> device_release_driver_internal+0x15b/0x230
> serio_handle_event+0x1c8/0x260
> process_one_work+0x215/0x620
> worker_thread+0x48/0x3a0
> kthread+0xfb/0x130
> ret_from_fork+0x3a/0x50
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(psmouse_mutex);
> lock(kn->count#130);
> lock(psmouse_mutex);
> lock(kn->count#130);
>
> *** DEADLOCK ***
>
> 6 locks held by kworker/0:3/102:
> #0: ((wq_completion)"events_long"){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
> #1: (serio_event_work){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
> #2: (serio_mutex){+.+.}, at: [<00000000c8a49847>] serio_handle_event+0x23/0x260
> #3: (&dev->mutex){....}, at: [<00000000b55eee75>] device_release_driver_internal+0x2f/0x230
> #4: (&serio->drv_mutex){+.+.}, at: [<000000009719f997>] serio_disconnect_driver+0x16/0x40
> #5: (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
>
> stack backtrace:
> CPU: 0 PID: 102 Comm: kworker/0:3 Tainted: G U 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1
> Hardware name: LENOVO 74591P0/74591P0, BIOS 6DET28WW (1.05 ) 07/30/2008
> Workqueue: events_long serio_handle_event
> Call Trace:
> dump_stack+0x5f/0x86
> print_circular_bug.isra.18+0x1d0/0x2c0
> __lock_acquire+0x14ae/0x1b60
> ? kernfs_remove_by_name_ns+0x20/0x80
> ? lock_acquire+0xaf/0x200
> lock_acquire+0xaf/0x200
> ? kernfs_remove_by_name_ns+0x3b/0x80
> __kernfs_remove+0x243/0x2b0
> ? kernfs_remove_by_name_ns+0x3b/0x80
> ? kernfs_name_hash+0xd/0x70
> ? kernfs_find_ns+0x7e/0x100
> kernfs_remove_by_name_ns+0x3b/0x80
> remove_files.isra.0+0x2b/0x60
> sysfs_remove_group+0x38/0x80
> sysfs_remove_groups+0x24/0x40
> trackpoint_disconnect+0x2c/0x50
> psmouse_disconnect+0x8f/0x160
> serio_disconnect_driver+0x28/0x40
> serio_driver_remove+0xc/0x10
> device_release_driver_internal+0x15b/0x230
> serio_handle_event+0x1c8/0x260
> process_one_work+0x215/0x620
> worker_thread+0x48/0x3a0
> ? _raw_spin_unlock_irqrestore+0x4c/0x60
> kthread+0xfb/0x130
> ? process_one_work+0x620/0x620
> ? _kthread_create_on_node+0x30/0x30
> ret_from_fork+0x3a/0x50
>
> Signed-off-by: Daniel Vetter <[email protected]>
> Cc: Dmitry Torokhov <[email protected]>
> Cc: Benjamin Tissoires <[email protected]>
> Cc: Daniel Vetter <[email protected]>
> Cc: Arvind Yadav <[email protected]>
> Cc: Stephen Lyons <[email protected]>
> Cc: [email protected]
> ---
> drivers/input/mouse/psmouse-base.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
> index 8900c3166ebf..06ccd8e22f3c 100644
> --- a/drivers/input/mouse/psmouse-base.c
> +++ b/drivers/input/mouse/psmouse-base.c
> @@ -1484,8 +1484,10 @@ static void psmouse_disconnect(struct serio *serio)
> psmouse_deactivate(parent);
> }
>
> + mutex_unlock(&psmouse_mutex);
> if (psmouse->disconnect)
> psmouse->disconnect(psmouse);
> + mutex_lock(&psmouse_mutex);
Why do you think it is proper to drop this mutex? It is introduced for a
reason.
I think the trace you are seeing is due to:
commit 988cd7afb3f37598891ca70b4c6eb914c338c46a
Author: Tejun Heo <[email protected]>
Date: Mon Feb 3 14:02:58 2014 -0500
kernfs: remove kernfs_addrm_cxt
where we started taking kernfs_mutex when adding/removing sysfs files.
Ultimately I think we may have to change switching protocol to a work
item to be done asynchronously from writing to sysfs attribute.
Thanks.
--
Dmitry
On Mon, Apr 30, 2018 at 11:17 PM, Dmitry Torokhov
<[email protected]> wrote:
> Hi Daniel,
>
> On Mon, Apr 30, 2018 at 09:56:49PM +0200, Daniel Vetter wrote:
>> At least trackpoint_disconnect wants to remove some sysfs files, and
>> we can't remove sysfs files while holding psmouse_mutex:
>>
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1 Tainted: G U
>> ------------------------------------------------------
>> kworker/0:3/102 is trying to acquire lock:
>> (kn->count#130){++++}, at: [<000000009679748b>] kernfs_remove_by_name_ns+0x3b/0x80
>>
>> but task is already holding lock:
>> (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
>>
>> which lock already depends on the new lock.
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #1 (psmouse_mutex){+.+.}:
>> psmouse_attr_set_helper+0x28/0x140
>> kernfs_fop_write+0xfe/0x180
>> __vfs_write+0x1e/0x130
>> vfs_write+0xbd/0x1b0
>> SyS_write+0x40/0xa0
>> do_syscall_64+0x65/0x1a0
>> entry_SYSCALL_64_after_hwframe+0x42/0xb7
>>
>> -> #0 (kn->count#130){++++}:
>> __kernfs_remove+0x243/0x2b0
>> kernfs_remove_by_name_ns+0x3b/0x80
>> remove_files.isra.0+0x2b/0x60
>> sysfs_remove_group+0x38/0x80
>> sysfs_remove_groups+0x24/0x40
>> trackpoint_disconnect+0x2c/0x50
>> psmouse_disconnect+0x8f/0x160
>> serio_disconnect_driver+0x28/0x40
>> serio_driver_remove+0xc/0x10
>> device_release_driver_internal+0x15b/0x230
>> serio_handle_event+0x1c8/0x260
>> process_one_work+0x215/0x620
>> worker_thread+0x48/0x3a0
>> kthread+0xfb/0x130
>> ret_from_fork+0x3a/0x50
>>
>> other info that might help us debug this:
>>
>> Possible unsafe locking scenario:
>>
>> CPU0 CPU1
>> ---- ----
>> lock(psmouse_mutex);
>> lock(kn->count#130);
>> lock(psmouse_mutex);
>> lock(kn->count#130);
>>
>> *** DEADLOCK ***
>>
>> 6 locks held by kworker/0:3/102:
>> #0: ((wq_completion)"events_long"){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
>> #1: (serio_event_work){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
>> #2: (serio_mutex){+.+.}, at: [<00000000c8a49847>] serio_handle_event+0x23/0x260
>> #3: (&dev->mutex){....}, at: [<00000000b55eee75>] device_release_driver_internal+0x2f/0x230
>> #4: (&serio->drv_mutex){+.+.}, at: [<000000009719f997>] serio_disconnect_driver+0x16/0x40
>> #5: (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
>>
>> stack backtrace:
>> CPU: 0 PID: 102 Comm: kworker/0:3 Tainted: G U 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1
>> Hardware name: LENOVO 74591P0/74591P0, BIOS 6DET28WW (1.05 ) 07/30/2008
>> Workqueue: events_long serio_handle_event
>> Call Trace:
>> dump_stack+0x5f/0x86
>> print_circular_bug.isra.18+0x1d0/0x2c0
>> __lock_acquire+0x14ae/0x1b60
>> ? kernfs_remove_by_name_ns+0x20/0x80
>> ? lock_acquire+0xaf/0x200
>> lock_acquire+0xaf/0x200
>> ? kernfs_remove_by_name_ns+0x3b/0x80
>> __kernfs_remove+0x243/0x2b0
>> ? kernfs_remove_by_name_ns+0x3b/0x80
>> ? kernfs_name_hash+0xd/0x70
>> ? kernfs_find_ns+0x7e/0x100
>> kernfs_remove_by_name_ns+0x3b/0x80
>> remove_files.isra.0+0x2b/0x60
>> sysfs_remove_group+0x38/0x80
>> sysfs_remove_groups+0x24/0x40
>> trackpoint_disconnect+0x2c/0x50
>> psmouse_disconnect+0x8f/0x160
>> serio_disconnect_driver+0x28/0x40
>> serio_driver_remove+0xc/0x10
>> device_release_driver_internal+0x15b/0x230
>> serio_handle_event+0x1c8/0x260
>> process_one_work+0x215/0x620
>> worker_thread+0x48/0x3a0
>> ? _raw_spin_unlock_irqrestore+0x4c/0x60
>> kthread+0xfb/0x130
>> ? process_one_work+0x620/0x620
>> ? _kthread_create_on_node+0x30/0x30
>> ret_from_fork+0x3a/0x50
>>
>> Signed-off-by: Daniel Vetter <[email protected]>
>> Cc: Dmitry Torokhov <[email protected]>
>> Cc: Benjamin Tissoires <[email protected]>
>> Cc: Daniel Vetter <[email protected]>
>> Cc: Arvind Yadav <[email protected]>
>> Cc: Stephen Lyons <[email protected]>
>> Cc: [email protected]
>> ---
>> drivers/input/mouse/psmouse-base.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
>> index 8900c3166ebf..06ccd8e22f3c 100644
>> --- a/drivers/input/mouse/psmouse-base.c
>> +++ b/drivers/input/mouse/psmouse-base.c
>> @@ -1484,8 +1484,10 @@ static void psmouse_disconnect(struct serio *serio)
>> psmouse_deactivate(parent);
>> }
>>
>> + mutex_unlock(&psmouse_mutex);
>> if (psmouse->disconnect)
>> psmouse->disconnect(psmouse);
>> + mutex_lock(&psmouse_mutex);
>
> Why do you think it is proper to drop this mutex? It is introduced for a
> reason.
>
> I think the trace you are seeing is due to:
>
> commit 988cd7afb3f37598891ca70b4c6eb914c338c46a
> Author: Tejun Heo <[email protected]>
> Date: Mon Feb 3 14:02:58 2014 -0500
>
> kernfs: remove kernfs_addrm_cxt
>
> where we started taking kernfs_mutex when adding/removing sysfs files.
> Ultimately I think we may have to change switching protocol to a work
> item to be done asynchronously from writing to sysfs attribute.
Well "holding a lock while adding/removing sysfs files and holding the
same lock from sysfs read/write callbacks" is a classic deadlock. I've
made lockdep shut up about it, I have no idea how to fix it properly.
kernfs switching it's locking doesn't change anything here.
Generally the fix is to untangle the locking: You need 1 set of locks
to protect the datastructures exposed through sysfs, and another thing
(maybe that's provided by serio already, I have no idea) to make sure
you're ordering connect/disconnect handling correct and there's not
concurrent calls to this hooks. Assuming serio does give that
guarantee then there's no need to hold the lock while unregistering
the sysfs files (we could perhaps push the lock dropping down into
trackpoint_disconnect, but that's less maintainable imo since it's not
obvious in psmouse_disconnect what's going on), and my patch is
correct.
But I didn't do a full locking audit of what exactly serio guarantees,
and what exactly psmouse_mutex needs to protect (and where
psmouse_mutex is only held because it's convenient).
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
On Wed, May 2, 2018 at 11:06 AM Daniel Vetter <[email protected]> wrote:
>
> On Mon, Apr 30, 2018 at 11:17 PM, Dmitry Torokhov
> <[email protected]> wrote:
> > Hi Daniel,
> >
> > On Mon, Apr 30, 2018 at 09:56:49PM +0200, Daniel Vetter wrote:
> >> At least trackpoint_disconnect wants to remove some sysfs files, and
> >> we can't remove sysfs files while holding psmouse_mutex:
> >>
> >> ======================================================
> >> WARNING: possible circular locking dependency detected
> >> 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1 Tainted: G U
> >> ------------------------------------------------------
> >> kworker/0:3/102 is trying to acquire lock:
> >> (kn->count#130){++++}, at: [<000000009679748b>] kernfs_remove_by_name_ns+0x3b/0x80
> >>
> >> but task is already holding lock:
> >> (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
> >>
> >> which lock already depends on the new lock.
> >>
> >> the existing dependency chain (in reverse order) is:
> >>
> >> -> #1 (psmouse_mutex){+.+.}:
> >> psmouse_attr_set_helper+0x28/0x140
> >> kernfs_fop_write+0xfe/0x180
> >> __vfs_write+0x1e/0x130
> >> vfs_write+0xbd/0x1b0
> >> SyS_write+0x40/0xa0
> >> do_syscall_64+0x65/0x1a0
> >> entry_SYSCALL_64_after_hwframe+0x42/0xb7
> >>
> >> -> #0 (kn->count#130){++++}:
> >> __kernfs_remove+0x243/0x2b0
> >> kernfs_remove_by_name_ns+0x3b/0x80
> >> remove_files.isra.0+0x2b/0x60
> >> sysfs_remove_group+0x38/0x80
> >> sysfs_remove_groups+0x24/0x40
> >> trackpoint_disconnect+0x2c/0x50
> >> psmouse_disconnect+0x8f/0x160
> >> serio_disconnect_driver+0x28/0x40
> >> serio_driver_remove+0xc/0x10
> >> device_release_driver_internal+0x15b/0x230
> >> serio_handle_event+0x1c8/0x260
> >> process_one_work+0x215/0x620
> >> worker_thread+0x48/0x3a0
> >> kthread+0xfb/0x130
> >> ret_from_fork+0x3a/0x50
> >>
> >> other info that might help us debug this:
> >>
> >> Possible unsafe locking scenario:
> >>
> >> CPU0 CPU1
> >> ---- ----
> >> lock(psmouse_mutex);
> >> lock(kn->count#130);
> >> lock(psmouse_mutex);
> >> lock(kn->count#130);
> >>
> >> *** DEADLOCK ***
> >>
> >> 6 locks held by kworker/0:3/102:
> >> #0: ((wq_completion)"events_long"){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
> >> #1: (serio_event_work){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
> >> #2: (serio_mutex){+.+.}, at: [<00000000c8a49847>] serio_handle_event+0x23/0x260
> >> #3: (&dev->mutex){....}, at: [<00000000b55eee75>] device_release_driver_internal+0x2f/0x230
> >> #4: (&serio->drv_mutex){+.+.}, at: [<000000009719f997>] serio_disconnect_driver+0x16/0x40
> >> #5: (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160
> >>
> >> stack backtrace:
> >> CPU: 0 PID: 102 Comm: kworker/0:3 Tainted: G U 4.16.0-rc5-g613eb885b69e-drmtip_1+ #1
> >> Hardware name: LENOVO 74591P0/74591P0, BIOS 6DET28WW (1.05 ) 07/30/2008
> >> Workqueue: events_long serio_handle_event
> >> Call Trace:
> >> dump_stack+0x5f/0x86
> >> print_circular_bug.isra.18+0x1d0/0x2c0
> >> __lock_acquire+0x14ae/0x1b60
> >> ? kernfs_remove_by_name_ns+0x20/0x80
> >> ? lock_acquire+0xaf/0x200
> >> lock_acquire+0xaf/0x200
> >> ? kernfs_remove_by_name_ns+0x3b/0x80
> >> __kernfs_remove+0x243/0x2b0
> >> ? kernfs_remove_by_name_ns+0x3b/0x80
> >> ? kernfs_name_hash+0xd/0x70
> >> ? kernfs_find_ns+0x7e/0x100
> >> kernfs_remove_by_name_ns+0x3b/0x80
> >> remove_files.isra.0+0x2b/0x60
> >> sysfs_remove_group+0x38/0x80
> >> sysfs_remove_groups+0x24/0x40
> >> trackpoint_disconnect+0x2c/0x50
> >> psmouse_disconnect+0x8f/0x160
> >> serio_disconnect_driver+0x28/0x40
> >> serio_driver_remove+0xc/0x10
> >> device_release_driver_internal+0x15b/0x230
> >> serio_handle_event+0x1c8/0x260
> >> process_one_work+0x215/0x620
> >> worker_thread+0x48/0x3a0
> >> ? _raw_spin_unlock_irqrestore+0x4c/0x60
> >> kthread+0xfb/0x130
> >> ? process_one_work+0x620/0x620
> >> ? _kthread_create_on_node+0x30/0x30
> >> ret_from_fork+0x3a/0x50
> >>
> >> Signed-off-by: Daniel Vetter <[email protected]>
> >> Cc: Dmitry Torokhov <[email protected]>
> >> Cc: Benjamin Tissoires <[email protected]>
> >> Cc: Daniel Vetter <[email protected]>
> >> Cc: Arvind Yadav <[email protected]>
> >> Cc: Stephen Lyons <[email protected]>
> >> Cc: [email protected]
> >> ---
> >> drivers/input/mouse/psmouse-base.c | 2 ++
> >> 1 file changed, 2 insertions(+)
> >>
> >> diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
> >> index 8900c3166ebf..06ccd8e22f3c 100644
> >> --- a/drivers/input/mouse/psmouse-base.c
> >> +++ b/drivers/input/mouse/psmouse-base.c
> >> @@ -1484,8 +1484,10 @@ static void psmouse_disconnect(struct serio *serio)
> >> psmouse_deactivate(parent);
> >> }
> >>
> >> + mutex_unlock(&psmouse_mutex);
> >> if (psmouse->disconnect)
> >> psmouse->disconnect(psmouse);
> >> + mutex_lock(&psmouse_mutex);
> >
> > Why do you think it is proper to drop this mutex? It is introduced for a
> > reason.
> >
> > I think the trace you are seeing is due to:
> >
> > commit 988cd7afb3f37598891ca70b4c6eb914c338c46a
> > Author: Tejun Heo <[email protected]>
> > Date: Mon Feb 3 14:02:58 2014 -0500
> >
> > kernfs: remove kernfs_addrm_cxt
> >
> > where we started taking kernfs_mutex when adding/removing sysfs files.
> > Ultimately I think we may have to change switching protocol to a work
> > item to be done asynchronously from writing to sysfs attribute.
>
> Well "holding a lock while adding/removing sysfs files and holding the
> same lock from sysfs read/write callbacks" is a classic deadlock. I've
> made lockdep shut up about it, I have no idea how to fix it properly.
> kernfs switching it's locking doesn't change anything here.
>
> Generally the fix is to untangle the locking: You need 1 set of locks
> to protect the datastructures exposed through sysfs, and another thing
> (maybe that's provided by serio already, I have no idea) to make sure
> you're ordering connect/disconnect handling correct and there's not
> concurrent calls to this hooks. Assuming serio does give that
> guarantee then there's no need to hold the lock while unregistering
> the sysfs files (we could perhaps push the lock dropping down into
> trackpoint_disconnect, but that's less maintainable imo since it's not
> obvious in psmouse_disconnect what's going on), and my patch is
> correct.
>
> But I didn't do a full locking audit of what exactly serio guarantees,
> and what exactly psmouse_mutex needs to protect (and where
> psmouse_mutex is only held because it's convenient).
Ping? Just noticed that I still have this bugfix hanging around.
bugfix as in "make lockdep more useful", not necessarily fixing the
locking here properly. I guess I could respin to add a FIXME comment,
but not sure how useful that would be.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch