Re: [PATCH] thermal: Fix race condition in suspend/resume

["Bo Ye (叶波)" <Bo.Ye@mediatek.com>]

On Wed, 2023-10-25 at 20:21 +0200, Rafael J. Wysocki wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On Mon, Oct 23, 2023 at 3:20 AM Bo Ye (叶波) <Bo.Ye@mediatek.com>
> wrote:
> >
> > Yes, it is observed issue.
> 
> It does happen, so it's not just "potential" and the subject of the
> patch is slightly misleading.  Please adjust it.

Done

> 
> > Firstly, it needs to be clarified that this issue occurs in a real-
> > world environment. By analyzing the logs, we inferred that the
> issue
> > occurred just as the system was entering suspend mode, and the user
> was
> > switching the thermal policy (this action causes all thermal zones
> to
> > unregister/register). In addition, we conducted degradation tests
> and
> > also reproduced this issue. The specific method is to first switch
> the
> > thermal policy through a command, and then immediately put the
> system
> > into suspend state through another command. This method can also
> > reproduce the issue.
> 
> OK, so please add this information to the patch changelog.
> 
> > On Thu, 2023-10-12 at 07:35 +0000, Bo Ye (叶波) wrote:
> > > On Sat, 2023-09-16 at 19:33 +0800, Bo Ye wrote:
> > >
> > > Correct mail title format: remove "Subject:" from mail title.
> > >
> > > > From: "yugang.wang" <yugang.wang@mediatek.com>
> > > >
> > > > Body:
> > > > This patch fixes a race condition during system resume. It
> occurs
> > > > if
> > > > the system is exiting a suspend state and a user is trying to
> > > > register/unregister a thermal zone concurrently. The root cause
> is
> > > > that both actions access the `thermal_tz_list`.
> > > >
> > > > In detail:
> > > >
> > > > 1. At PM_POST_SUSPEND during the resume, the system reads all
> > > > thermal
> > > >    zones in `thermal_tz_list`, then resets and updates their
> > > >    temperatures.
> > > > 2. When registering/unregistering a thermal zone, the
> > > >    `thermal_tz_list` gets manipulated.
> > > >
> > > > These two actions might occur concurrently, causing a race
> > > > condition.
> > > > To solve this issue, we introduce a mutex lock to protect
> > > > `thermal_tz_list` from being modified while it's being read and
> > > > updated during the resume from suspend.
> > > >
> > > > Kernel oops excerpt related to this fix:
> > > >
> > > > [ 5201.869845] [T316822] pc: [0xffffffeb7d4876f0]
> > > > mutex_lock+0x34/0x170
> > > > [ 5201.869856] [T316822] lr: [0xffffffeb7ca98a84]
> > > > thermal_pm_notify+0xd4/0x26c
> > > > [... cut for brevity ...]
> > > > [ 5201.871061] [T316822]  suspend_prepare+0x150/0x470
> > > > [ 5201.871067] [T316822]  enter_state+0x84/0x6f4
> > > > [ 5201.871076] [T316822]  state_store+0x15c/0x1e8
> 
> Well, the connection between the above log snippet and the issue
> addressed by the patch is rather hard to establish.  Please include
> more of the oops information.

Thank you very much for reviewing the additional explanations.

1.Enable thermal policy operation will unregister/register all thermal
zones
10-21 06:13:59.280   854   922 I libMtcLoader: enable thermal policy
thermal_policy_09.

2.System suspend entry time is 2023-10-20 22:13:59.242
[ 4106.364175][T609387] binder:534_2: [name:spm&][SPM] PM: suspend
entry 2023-10-20 22:13:59.242898243 UTC
[ 4106.366185][T609387] binder:534_2: PM: [name:wakeup&]PM: Pending
Wakeup Sources: NETLINK

3. It can be proven that the absence of a switch strategy will perform
unregister/register operations on thermal zones (android time is 2023-
10-20 22:13:59.282)，
Because the logs for other thermal zones switching are not enabled by
default, we cannot see the logs related to other thermal zones.
[ 4106.404167][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_unbind unbinding OK
[ 4106.404215][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_unbind unbinding OK
[ 4106.404225][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_unbind unbinding OK
[ 4106.404504][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_bind binding OK, 0
[ 4106.404545][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_bind binding OK, 2
[ 4106.404566][T600922] mtkPowerMsgHdl:
[name:thermal_monitor&][Thermal/TZ/CPU]tscpu_bind binding OK, 1

4. thermal_pm_notify trigger KE(android time:  2023-10-20 22:13:59.
315894)
[ 4106.437171][T209387] binder:534_2: [name:mrdump&]Kernel Offset:
0x289cc80000 from 0xffffffc008000000
[ 4106.437182][T209387] binder:534_2: [name:mrdump&]PHYS_OFFSET:
0x40000000
[ 4106.437191][T209387] binder:534_2: [name:mrdump&]pstate: 80400005
(Nzcv daif +PAN -UAO)
[ 4106.437204][T209387] binder:534_2: [name:mrdump&]pc :
[0xffffffe8a6688200] mutex_lock+0x34/0x184
[ 4106.437214][T209387] binder:534_2: [name:mrdump&]lr :
[0xffffffe8a5ce66bc] thermal_pm_notify+0xd4/0x26c
[ 4106.437220][T209387] binder:534_2: [name:mrdump&]sp :
ffffffc01bab3ae0
[ 4106.437226][T209387] binder:534_2: [name:mrdump&]x29:
ffffffc01bab3af0 x28: 0000000000000001

> 
> > > >
> > > > Change-Id: Ifdbdecba17093f91eab7e36ce04b46d311ca6568
> > > > Signed-off-by: yugang.wang <yugang.wang@mediatek.com>
> > > > Signed-off-by: Bo Ye <bo.ye@mediatek.com>
> > > > ---
> > > >  drivers/thermal/thermal_core.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/thermal/thermal_core.c
> > > > b/drivers/thermal/thermal_core.c
> > > > index 8717a3343512..a7a18ed57b6d 100644
> > > > --- a/drivers/thermal/thermal_core.c
> > > > +++ b/drivers/thermal/thermal_core.c
> > > > @@ -1529,12 +1529,14 @@ static int thermal_pm_notify(struct
> > > > notifier_block *nb,
> > > >     case PM_POST_HIBERNATION:
> > > >     case PM_POST_RESTORE:
> > > >     case PM_POST_SUSPEND:
> > > > +           mutex_lock(&thermal_list_lock);
> > > >             atomic_set(&in_suspend, 0);
> 
> It is not clear to me why the above statement needs to be under the
> lock.
> 
> > > >             list_for_each_entry(tz, &thermal_tz_list, node) {
> > > >                     thermal_zone_device_init(tz);
> > > >                     thermal_zone_device_update(tz,
> > >
> >                                                THERMAL_EVENT_UNSPEC
> > > > IFIED);
> > > >             }
> > > > +           mutex_unlock(&thermal_list_lock);
> > > >             break;
> > > >     default:
> > > >             break;