Re: [PATCH v3] hwspinlock: allow sharing of hwspinlocks

From: Fabien DESSENNE
Date: Tue Dec 03 2019 - 05:02:42 EST

Hi


Feel free to share your comments :)

As a reminder, below are two examples that explain the need for this patch.
In both cases the Linux clients are talking to a single entity on the
remote-side.

Example 1:
ÂÂÂ exti: interrupt-controller@5000d000 {
ÂÂÂ ÂÂÂ compatible = "st,stm32mp1-exti", "syscon";

ÂÂÂ ÂÂÂ hwlocks = <&hsem 1>;

ÂÂÂÂÂÂ ...
ÂÂÂ };
The two drivers (stm32mp1-exti and syscon) refer to the same hwlock.
With the current hwspinlock implementation, only the first driver
succeeds in requesting (hwspin_lock_request_specific) the hwlock. The
second request fails.


Example 2:
Here it is more a question of optimization : we want to save the number
of hwlocks used to protect resources, using an unique hwlock to protect
all pinctrl resources:
ÂÂÂ ÂÂÂ pinctrl: pin-controller@50002000 {
ÂÂÂ ÂÂÂ ÂÂÂ compatible = "st,stm32mp157-pinctrl";
ÂÂÂ ÂÂÂ ÂÂÂ hwlocks = <&hsem 0 1>;

ÂÂÂÂÂÂÂÂÂÂÂ ...
ÂÂÂ ÂÂÂ pinctrl_z: pin-controller-z@54004000 {
ÂÂÂ ÂÂÂ ÂÂÂ compatible = "st,stm32mp157-z-pinctrl";
ÂÂÂ ÂÂÂ ÂÂÂ hwlocks = <&hsem 0 1>;

      ...


BR

Fabien


On 10/10/2019 5:19 PM, Fabien DESSENNE wrote:
> Hi Bjorn, Suman, and others
>
> Do you have any comments regarding this patch?
>
> BR
> Fabien
>
>
>> -----Original Message-----
>> From: Fabien DESSENNE <fabien.dessenne@xxxxxx>
>> Sent: mercredi 11 septembre 2019 15:57
>> To: Ohad Ben-Cohen <ohad@xxxxxxxxxx>; Bjorn Andersson
>> <bjorn.andersson@xxxxxxxxxx>; Suman Anna <s-anna@xxxxxx>; Jonathan Corbet
>> <corbet@xxxxxxx>; linux-remoteproc@xxxxxxxxxxxxxxx; linux-
>> doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>> Cc: Fabien DESSENNE <fabien.dessenne@xxxxxx>; linux-stm32@st-md-
>> mailman.stormreply.com
>> Subject: [PATCH v3] hwspinlock: allow sharing of hwspinlocks
>>
>> Allow several clients to request (hwspin_lock_request_specific()) the same lock.
>> In addition to that, protect a given lock from being locked
>> (hwspin_trylock{_...}()) by more that one client at a time.
>>
>> Since the RAW and IN_ATOMIC modes do not implement that protection (unlike
>> the default, IRQ and IRQSTATE modes that make use of spin_lock{_irq,
>> _irqsave}), protect __hwspin_trylock with the atomic bitop test_and_set_bit().
>> This bitop is atomic (SMP-safe), does not disable neither preemption nor
>> interrupts, hence it preserves the RAW and IN_ATOMIC modes constraints.
>>
>> Signed-off-by: Fabien Dessenne <fabien.dessenne@xxxxxx>
>> ---
>> Changes since v2:
>> - Drop the DeviceTree-based implementation.
>> - Do not let the choice between exclusive and shared usage : locks are
>> always shared.
>> - Add a protection (atomic bitop) working in any modes to allow safe
>> sharing between clients.
>>
>> Changes since v1:
>> - Removed useless 'status = "okay"' from stm32mp157c.dtsi
>> ---
>> Documentation/hwspinlock.txt | 9 ++-
>> drivers/hwspinlock/hwspinlock_core.c | 98 +++++++++++++++++++++++------
>> ---
>> drivers/hwspinlock/hwspinlock_internal.h | 4 ++
>> 3 files changed, 81 insertions(+), 30 deletions(-)
>>
>> diff --git a/Documentation/hwspinlock.txt b/Documentation/hwspinlock.txt index
>> 6f03713..5f6f660 100644
>> --- a/Documentation/hwspinlock.txt
>> +++ b/Documentation/hwspinlock.txt
>> @@ -53,9 +53,8 @@ Should be called from a process context (might sleep).
>>
>> struct hwspinlock *hwspin_lock_request_specific(unsigned int id);
>>
>> -Assign a specific hwspinlock id and return its address, or NULL -if that
>> hwspinlock is already in use. Usually board code will -be calling this function in
>> order to reserve specific hwspinlock
>> +Assign a specific hwspinlock id and return its address. Usually board
>> +code will be calling this function in order to reserve specific
>> +hwspinlock
>> ids for predefined purposes.
>>
>> Should be called from a process context (might sleep).
>> @@ -449,11 +448,15 @@ of which represents a single hardware lock::
>> * struct hwspinlock - this struct represents a single hwspinlock instance
>> * @bank: the hwspinlock_device structure which owns this lock
>> * @lock: initialized and used by hwspinlock core
>> + * @is_locked: whether this lock is currently locked
>> + * @reqcount: number of users having requested this lock
>> * @priv: private data, owned by the underlying platform-specific
>> hwspinlock drv
>> */
>> struct hwspinlock {
>> struct hwspinlock_device *bank;
>> spinlock_t lock;
>> + unsigned long is_locked;
>> + unsigned int reqcount;
>> void *priv;
>> };
>>
>> diff --git a/drivers/hwspinlock/hwspinlock_core.c
>> b/drivers/hwspinlock/hwspinlock_core.c
>> index 8862445..e9d3de10 100644
>> --- a/drivers/hwspinlock/hwspinlock_core.c
>> +++ b/drivers/hwspinlock/hwspinlock_core.c
>> @@ -29,6 +29,7 @@
>>
>> /* radix tree tags */
>> #define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */
>> +#define HWSPINLOCK_DYN_ASSIGN (1) /* dynamically assigned
>> hwspinlock */
>>
>> /*
>> * A radix tree is used to maintain the available hwspinlock instances.
>> @@ -96,14 +97,25 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
>> mode, unsigned long *flags)
>> BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
>>
>> /*
>> + * Check if the lock is already taken by another context on the local
>> + * cpu.
>> + * Calling atomic test_and_set_bit_lock() ensures that hwspinlock is
>> + * SMP-safe (so we can take it from additional contexts on the local
>> + * host) in any mode, even those where we do not make use of the local
>> + * spinlock.
>> + */
>> +
>> + if (test_and_set_bit_lock(0, &hwlock->is_locked))
>> + return -EBUSY;
>> +
>> + /*
>> * This spin_lock{_irq, _irqsave} serves three purposes:
>> *
>> * 1. Disable preemption, in order to minimize the period of time
>> * in which the hwspinlock is taken. This is important in order
>> * to minimize the possible polling on the hardware interconnect
>> * by a remote user of this lock.
>> - * 2. Make the hwspinlock SMP-safe (so we can take it from
>> - * additional contexts on the local host).
>> + * 2. Make the hwspinlock SMP-safe.
>> * 3. Ensure that in_atomic/might_sleep checks catch potential
>> * problems with hwspinlock usage (e.g. scheduler checks like
>> * 'scheduling while atomic' etc.)
>> @@ -124,9 +136,9 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
>> mode, unsigned long *flags)
>> break;
>> }
>>
>> - /* is lock already taken by another context on the local cpu ? */
>> + /* sanity check (this shouldn't happen) */
>> if (!ret)
>> - return -EBUSY;
>> + goto clear;
>>
>> /* try to take the hwspinlock device */
>> ret = hwlock->bank->ops->trylock(hwlock);
>> @@ -149,7 +161,7 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
>> mode, unsigned long *flags)
>> break;
>> }
>>
>> - return -EBUSY;
>> + goto clear;
>> }
>>
>> /*
>> @@ -165,6 +177,11 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
>> mode, unsigned long *flags)
>> mb();
>>
>> return 0;
>> +
>> +clear:
>> + /* Clear is_locked */
>> + clear_bit_unlock(0, &hwlock->is_locked);
>> + return -EBUSY;
>> }
>> EXPORT_SYMBOL_GPL(__hwspin_trylock);
>>
>> @@ -299,6 +316,9 @@ void __hwspin_unlock(struct hwspinlock *hwlock, int
>> mode, unsigned long *flags)
>> spin_unlock(&hwlock->lock);
>> break;
>> }
>> +
>> + /* Clear is_locked set while locking */
>> + clear_bit_unlock(0, &hwlock->is_locked);
>> }
>> EXPORT_SYMBOL_GPL(__hwspin_unlock);
>>
>> @@ -504,7 +524,9 @@ int hwspin_lock_register(struct hwspinlock_device *bank,
>> struct device *dev,
>> hwlock = &bank->lock[i];
>>
>> spin_lock_init(&hwlock->lock);
>> + clear_bit(0, &hwlock->is_locked);
>> hwlock->bank = bank;
>> + hwlock->reqcount = 0;
>>
>> ret = hwspin_lock_register_single(hwlock, base_id + i);
>> if (ret)
>> @@ -664,12 +686,16 @@ static int __hwspin_lock_request(struct hwspinlock
>> *hwlock)
>> return ret;
>> }
>>
>> - /* mark hwspinlock as used, should not fail */
>> - tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock),
>> - HWSPINLOCK_UNUSED);
>> + /* update reqcount */
>> + if (!hwlock->reqcount++) {
>> + /* first request, mark hwspinlock as used, should not fail */
>> + tmp = radix_tree_tag_clear(&hwspinlock_tree,
>> + hwlock_to_id(hwlock),
>> + HWSPINLOCK_UNUSED);
>>
>> - /* self-sanity check that should never fail */
>> - WARN_ON(tmp != hwlock);
>> + /* self-sanity check that should never fail */
>> + WARN_ON(tmp != hwlock);
>> + }
>>
>> return ret;
>> }
>> @@ -706,7 +732,7 @@ EXPORT_SYMBOL_GPL(hwspin_lock_get_id);
>> */
>> struct hwspinlock *hwspin_lock_request(void) {
>> - struct hwspinlock *hwlock;
>> + struct hwspinlock *hwlock, *tmp;
>> int ret;
>>
>> mutex_lock(&hwspinlock_tree_lock);
>> @@ -728,6 +754,13 @@ struct hwspinlock *hwspin_lock_request(void)
>> if (ret < 0)
>> hwlock = NULL;
>>
>> + /* mark this hwspinlock as dynamically assigned */
>> + tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
>> + HWSPINLOCK_DYN_ASSIGN);
>> +
>> + /* self-sanity check which should never fail */
>> + WARN_ON(tmp != hwlock);
>> +
>> out:
>> mutex_unlock(&hwspinlock_tree_lock);
>> return hwlock;
>> @@ -764,18 +797,19 @@ struct hwspinlock
>> *hwspin_lock_request_specific(unsigned int id)
>> /* sanity check (this shouldn't happen) */
>> WARN_ON(hwlock_to_id(hwlock) != id);
>>
>> - /* make sure this hwspinlock is unused */
>> - ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
>> - if (ret == 0) {
>> - pr_warn("hwspinlock %u is already in use\n", id);
>> + /* mark as used and power up */
>> + ret = __hwspin_lock_request(hwlock);
>> + if (ret < 0) {
>> hwlock = NULL;
>> goto out;
>> }
>>
>> - /* mark as used and power up */
>> - ret = __hwspin_lock_request(hwlock);
>> - if (ret < 0)
>> - hwlock = NULL;
>> + /*
>> + * warn if this lock is also used by another client which got this lock
>> + * with dynamic assignment using the hwspin_lock_request() API
>> + */
>> + if (radix_tree_tag_get(&hwspinlock_tree, id,
>> HWSPINLOCK_DYN_ASSIGN))
>> + pr_warn("hwspinlock %u is shared with a 'dynamic' user\n", id);
>>
>> out:
>> mutex_unlock(&hwspinlock_tree_lock);
>> @@ -799,7 +833,7 @@ int hwspin_lock_free(struct hwspinlock *hwlock) {
>> struct device *dev;
>> struct hwspinlock *tmp;
>> - int ret;
>> + int ret, id;
>>
>> if (!hwlock) {
>> pr_err("invalid hwlock\n");
>> @@ -810,30 +844,40 @@ int hwspin_lock_free(struct hwspinlock *hwlock)
>> mutex_lock(&hwspinlock_tree_lock);
>>
>> /* make sure the hwspinlock is used */
>> - ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock),
>> - HWSPINLOCK_UNUSED);
>> + id = hwlock_to_id(hwlock);
>> + ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
>> if (ret == 1) {
>> dev_err(dev, "%s: hwlock is already free\n", __func__);
>> dump_stack();
>> ret = -EINVAL;
>> - goto out;
>> + goto out_unlock;
>> }
>>
>> /* notify the underlying device that power is not needed */
>> ret = pm_runtime_put(dev);
>> if (ret < 0)
>> - goto out;
>> + goto out_unlock;
>> +
>> + /* update reqcount */
>> + if (--hwlock->reqcount)
>> + goto out_put;
>>
>> /* mark this hwspinlock as available */
>> - tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
>> - HWSPINLOCK_UNUSED);
>> + tmp = radix_tree_tag_set(&hwspinlock_tree, id,
>> HWSPINLOCK_UNUSED);
>>
>> /* sanity check (this shouldn't happen) */
>> WARN_ON(tmp != hwlock);
>>
>> + /* clear the dynamically assigned tag */
>> + tmp = radix_tree_tag_clear(&hwspinlock_tree, id,
>> +HWSPINLOCK_DYN_ASSIGN);
>> +
>> + /* self-sanity check which should never fail */
>> + WARN_ON(tmp != hwlock);
>> +
>> +out_put:
>> module_put(dev->driver->owner);
>>
>> -out:
>> +out_unlock:
>> mutex_unlock(&hwspinlock_tree_lock);
>> return ret;
>> }
>> diff --git a/drivers/hwspinlock/hwspinlock_internal.h
>> b/drivers/hwspinlock/hwspinlock_internal.h
>> index 9eb6bd0..a3aae55 100644
>> --- a/drivers/hwspinlock/hwspinlock_internal.h
>> +++ b/drivers/hwspinlock/hwspinlock_internal.h
>> @@ -35,11 +35,15 @@ struct hwspinlock_ops {
>> * struct hwspinlock - this struct represents a single hwspinlock instance
>> * @bank: the hwspinlock_device structure which owns this lock
>> * @lock: initialized and used by hwspinlock core
>> + * @is_locked: whether this lock is currently locked
>> + * @reqcount: number of users having requested this lock
>> * @priv: private data, owned by the underlying platform-specific hwspinlock drv
>> */
>> struct hwspinlock {
>> struct hwspinlock_device *bank;
>> spinlock_t lock;
>> + unsigned long is_locked;
>> + unsigned int reqcount;
>> void *priv;
>> };
>>
>> --
>> 2.7.4