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Date: Fri, 22 Jan 2021 17:39:11 +0100
From: Stephen Berman <stephen.berman@....net>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Linux ACPI <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Zhang Rui <rui.zhang@...el.com>,
Linux PM <linux-pm@...r.kernel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] ACPI: thermal: Do not call acpi_thermal_check() directly
On Fri, 22 Jan 2021 17:23:36 +0100 "Rafael J. Wysocki" <rafael@...nel.org> wrote:
> On Thu, Jan 14, 2021 at 7:35 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> Calling acpi_thermal_check() from acpi_thermal_notify() directly
>> is problematic if _TMP triggers Notify () on the thermal zone for
>> which it has been evaluated (which happens on some systems), because
>> it causes a new acpi_thermal_notify() invocation to be queued up
>> every time and if that takes place too often, an indefinite number of
>> pending work items may accumulate in kacpi_notify_wq over time.
>>
>> Besides, it is not really useful to queue up a new invocation of
>> acpi_thermal_check() if one of them is pending already.
>>
>> For these reasons, rework acpi_thermal_notify() to queue up a thermal
>> check instead of calling acpi_thermal_check() directly and only allow
>> one thermal check to be pending at a time. Moreover, only allow one
>> acpi_thermal_check_fn() instance at a time to run
>> thermal_zone_device_update() for one thermal zone and make it return
>> early if it sees other instances running for the same thermal zone.
>>
>> While at it, fold acpi_thermal_check() into acpi_thermal_check_fn(),
>> as it is only called from there after the other changes made here.
>>
>> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=208877
>> Reported-by: Stephen Berman <stephen.berman@....net>
>> Diagnosed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Well, it's been over a week since this was posted.
>
> Does anyone have any comments?
Sorry, I haven't been able to make time to test the patch yet, but I'll
try to do so this weekend. Is it just the patch below that I should
apply, ignoring the previous patches you sent? And can I apply it to
the current mainline kernel?
Thanks,
Steve Berman
>> ---
>> drivers/acpi/thermal.c | 46 +++++++++++++++++++++++++++++++++-------------
>> 1 file changed, 33 insertions(+), 13 deletions(-)
>>
>> Index: linux-pm/drivers/acpi/thermal.c
>> ===================================================================
>> --- linux-pm.orig/drivers/acpi/thermal.c
>> +++ linux-pm/drivers/acpi/thermal.c
>> @@ -174,6 +174,8 @@ struct acpi_thermal {
>> struct thermal_zone_device *thermal_zone;
>> int kelvin_offset; /* in millidegrees */
>> struct work_struct thermal_check_work;
>> + struct mutex thermal_check_lock;
>> + refcount_t thermal_check_count;
>> };
>>
>> /* --------------------------------------------------------------------------
>> @@ -495,14 +497,6 @@ static int acpi_thermal_get_trip_points(
>> return 0;
>> }
>>
>> -static void acpi_thermal_check(void *data)
>> -{
>> - struct acpi_thermal *tz = data;
>> -
>> - thermal_zone_device_update(tz->thermal_zone,
>> - THERMAL_EVENT_UNSPECIFIED);
>> -}
>> -
>> /* sys I/F for generic thermal sysfs support */
>>
>> static int thermal_get_temp(struct thermal_zone_device *thermal, int *temp)
>> @@ -900,6 +894,12 @@ static void acpi_thermal_unregister_ther
>> Driver Interface
>> -------------------------------------------------------------------------- */
>>
>> +static void acpi_queue_thermal_check(struct acpi_thermal *tz)
>> +{
>> + if (!work_pending(&tz->thermal_check_work))
>> + queue_work(acpi_thermal_pm_queue, &tz->thermal_check_work);
>> +}
>> +
>> static void acpi_thermal_notify(struct acpi_device *device, u32 event)
>> {
>> struct acpi_thermal *tz = acpi_driver_data(device);
>> @@ -910,17 +910,17 @@ static void acpi_thermal_notify(struct a
>>
>> switch (event) {
>> case ACPI_THERMAL_NOTIFY_TEMPERATURE:
>> - acpi_thermal_check(tz);
>> + acpi_queue_thermal_check(tz);
>> break;
>> case ACPI_THERMAL_NOTIFY_THRESHOLDS:
>> acpi_thermal_trips_update(tz, ACPI_TRIPS_REFRESH_THRESHOLDS);
>> - acpi_thermal_check(tz);
>> + acpi_queue_thermal_check(tz);
>> acpi_bus_generate_netlink_event(device->pnp.device_class,
>> dev_name(&device->dev), event, 0);
>> break;
>> case ACPI_THERMAL_NOTIFY_DEVICES:
>> acpi_thermal_trips_update(tz, ACPI_TRIPS_REFRESH_DEVICES);
>> - acpi_thermal_check(tz);
>> + acpi_queue_thermal_check(tz);
>> acpi_bus_generate_netlink_event(device->pnp.device_class,
>> dev_name(&device->dev), event, 0);
>> break;
>> @@ -1020,7 +1020,25 @@ static void acpi_thermal_check_fn(struct
>> {
>> struct acpi_thermal *tz = container_of(work, struct acpi_thermal,
>> thermal_check_work);
>> - acpi_thermal_check(tz);
>> +
>> + /*
>> + * In general, it is not sufficient to check the pending bit, because
>> + * subsequent instances of this function may be queued after one of them
>> + * has started running (e.g. if _TMP sleeps). Avoid bailing out if just
>> + * one of them is running, though, because it may have done the actual
>> + * check some time ago, so allow at least one of them to block on the
>> + * mutex while another one is running the update.
>> + */
>> + if (!refcount_dec_not_one(&tz->thermal_check_count))
>> + return;
>> +
>> + mutex_lock(&tz->thermal_check_lock);
>> +
>> + thermal_zone_device_update(tz->thermal_zone, THERMAL_EVENT_UNSPECIFIED);
>> +
>> + refcount_inc(&tz->thermal_check_count);
>> +
>> + mutex_unlock(&tz->thermal_check_lock);
>> }
>>
>> static int acpi_thermal_add(struct acpi_device *device)
>> @@ -1052,6 +1070,8 @@ static int acpi_thermal_add(struct acpi_
>> if (result)
>> goto free_memory;
>>
>> + refcount_set(&tz->thermal_check_count, 3);
>> + mutex_init(&tz->thermal_check_lock);
>> INIT_WORK(&tz->thermal_check_work, acpi_thermal_check_fn);
>>
>> pr_info(PREFIX "%s [%s] (%ld C)\n", acpi_device_name(device),
>> @@ -1117,7 +1137,7 @@ static int acpi_thermal_resume(struct de
>> tz->state.active |= tz->trips.active[i].flags.enabled;
>> }
>>
>> - queue_work(acpi_thermal_pm_queue, &tz->thermal_check_work);
>> + acpi_queue_thermal_check(tz);
>>
>> return AE_OK;
>> }
>>
>>
>>
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