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Subject[PATCH v2 2/2] platform/chrome: wilco_ec: Add circular buffer as event queue
Date
The current implementation of the event queue both
wastes space using a doubly linked list and isn't super
obvious in how it behaves. This converts the queue to an
actual circular buffer. The size of the queue is a
tunable module parameter. This also fixes a few other things:

- A memory leak that occurred when the ACPI device was
removed, but the events were not freed from the queue.
- Now kfree() the oldest event from outside all locks.
- Add newline to logging messages.
- Add helper macros to calculate size of events.
- Remove unneeded lock around a check for dev_data->exist
in hangup_device().
- Remove an unneeded null event pointer check in enqueue_events().
- Correct some comments.

Signed-off-by: Nick Crews <ncrews@chromium.org>
Reported-by: kbuild test robot <lkp@intel.com>
---

A v1 of this was applied to the chrome-platform-5.3 branch, but then
several errors were found, so Enric and Benson reverted the two commits.

v2 changes:
- Check if kmalloc() of queue fails (Colin Ian King)
- Use struct_size() macro when allocating the queue (Dan Carpenter)
- Remove unneeded semicolon after "if" in enqueue_events() (kbuild bot)
- Change nonseekable_open() to stream_open() (kbuild bot)
- Use kmemdup() for copying events to queue (YueHaibing)
- Wake up threads in enqueue_events() after every event, not
event_device_notify(), so listeners are guaranteed to be woken
(Dmitry Torokhov and Daniel Kurtz)
- Move lock back outside the queue, remove "full" boolean,
streamline pop() and push(), fix race condition where an queue
of size 1 could get doubly popped, move kfree() of oldest event
to outside the lock (Daniel Kurtz)

drivers/platform/chrome/wilco_ec/event.c | 258 +++++++++++++----------
1 file changed, 149 insertions(+), 109 deletions(-)

diff --git a/drivers/platform/chrome/wilco_ec/event.c b/drivers/platform/chrome/wilco_ec/event.c
index 1eed55681598..dba3d445623f 100644
--- a/drivers/platform/chrome/wilco_ec/event.c
+++ b/drivers/platform/chrome/wilco_ec/event.c
@@ -39,6 +39,7 @@
#include <linux/list.h>
#include <linux/module.h>
#include <linux/poll.h>
+#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/wait.h>

@@ -69,12 +70,110 @@ static DEFINE_IDA(event_ida);
/* Size of circular queue of events. */
#define MAX_NUM_EVENTS 64

+/**
+ * struct ec_event - Extended event returned by the EC.
+ * @size: Number of 16bit words in structure after the size word.
+ * @type: Extended event type, meaningless for us.
+ * @event: Event data words. Max count is %EC_ACPI_MAX_EVENT_WORDS.
+ */
+struct ec_event {
+ u16 size;
+ u16 type;
+ u16 event[0];
+} __packed;
+
+#define ec_event_num_words(ev) (ev->size - 1)
+#define ec_event_size(ev) (sizeof(*ev) + (ec_event_num_words(ev) * sizeof(u16)))
+
+/**
+ * struct ec_event_queue - Circular queue for events.
+ * @capacity: Number of elements the queue can hold.
+ * @head: Next index to write to.
+ * @tail: Next index to read from.
+ * @entries: Array of events.
+ */
+struct ec_event_queue {
+ int capacity;
+ int head;
+ int tail;
+ struct ec_event *entries[0];
+};
+
+/* Maximum number of events to store in ec_event_queue */
+static int queue_size = 64;
+module_param(queue_size, int, 0644);
+
+static struct ec_event_queue *event_queue_new(int capacity)
+{
+ struct ec_event_queue *q;
+
+ q = kzalloc(struct_size(q, entries, capacity), GFP_KERNEL);
+ if (!q)
+ return NULL;
+
+ q->capacity = capacity;
+
+ return q;
+}
+
+static inline bool event_queue_empty(struct ec_event_queue *q)
+{
+ /* head==tail when both full and empty, but head==NULL when empty */
+ return q->head == q->tail && !q->entries[q->head];
+}
+
+static inline bool event_queue_full(struct ec_event_queue *q)
+{
+ /* head==tail when both full and empty, but head!=NULL when full */
+ return q->head == q->tail && q->entries[q->head];
+}
+
+static struct ec_event *event_queue_pop(struct ec_event_queue *q)
+{
+ struct ec_event *ev;
+
+ if (event_queue_empty(q))
+ return NULL;
+
+ ev = q->entries[q->tail];
+ q->entries[q->tail] = NULL;
+ q->tail = (q->tail + 1) % q->capacity;
+
+ return ev;
+}
+
+/*
+ * If full, overwrite the oldest event and return it so the caller
+ * can kfree it. If not full, return NULL.
+ */
+static struct ec_event *event_queue_push(struct ec_event_queue *q,
+ struct ec_event *ev)
+{
+ struct ec_event *popped = NULL;
+
+ if (event_queue_full(q))
+ popped = event_queue_pop(q);
+ q->entries[q->head] = ev;
+ q->head = (q->head + 1) % q->capacity;
+
+ return popped;
+}
+
+static void event_queue_free(struct ec_event_queue *q)
+{
+ struct ec_event *event;
+
+ while ((event = event_queue_pop(q)) != NULL)
+ kfree(event);
+
+ kfree(q);
+}
+
/**
* struct event_device_data - Data for a Wilco EC device that responds to ACPI.
* @events: Circular queue of EC events to be provided to userspace.
- * @num_events: Number of events in the queue.
- * @lock: Mutex to guard the queue.
- * @wq: Wait queue to notify processes when events or available or the
+ * @queue_lock: Protect the queue from simultaneous read/writes.
+ * @wq: Wait queue to notify processes when events are available or the
* device has been removed.
* @cdev: Char dev that userspace reads() and polls() from.
* @dev: Device associated with the %cdev.
@@ -84,14 +183,13 @@ static DEFINE_IDA(event_ida);
*
* There will be one of these structs for each ACPI device registered. This data
* is the queue of events received from ACPI that still need to be read from
- * userspace (plus a supporting lock and wait queue), as well as the device and
- * char device that userspace is using, plus a flag on whether the ACPI device
- * has been removed.
+ * userspace, the device and char device that userspace is using, a wait queue
+ * used to notify different threads when something has changed, plus a flag
+ * on whether the ACPI device has been removed.
*/
struct event_device_data {
- struct list_head events;
- size_t num_events;
- struct mutex lock;
+ struct ec_event_queue *events;
+ spinlock_t queue_lock;
wait_queue_head_t wq;
struct device dev;
struct cdev cdev;
@@ -99,31 +197,6 @@ struct event_device_data {
atomic_t available;
};

-/**
- * struct ec_event - Extended event returned by the EC.
- * @size: Number of words in structure after the size word.
- * @type: Extended event type from &enum ec_event_type.
- * @event: Event data words. Max count is %EC_ACPI_MAX_EVENT_WORDS.
- */
-struct ec_event {
- u16 size;
- u16 type;
- u16 event[0];
-} __packed;
-
-/**
- * struct ec_event_entry - Event queue entry.
- * @list: List node.
- * @size: Number of bytes in event structure.
- * @event: Extended event returned by the EC. This should be the last
- * element because &struct ec_event includes a zero length array.
- */
-struct ec_event_entry {
- struct list_head list;
- size_t size;
- struct ec_event event;
-};
-
/**
* enqueue_events() - Place EC events in queue to be read by userspace.
* @adev: Device the events came from.
@@ -132,7 +205,7 @@ struct ec_event_entry {
*
* %buf contains a number of ec_event's, packed one after the other.
* Each ec_event is of variable length. Start with the first event, copy it
- * into a containing ev_event_entry, store that entry in a list, move on
+ * into a persistent ec_event, store that entry in the queue, move on
* to the next ec_event in buf, and repeat.
*
* Return: 0 on success or negative error code on failure.
@@ -140,25 +213,20 @@ struct ec_event_entry {
static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
{
struct event_device_data *dev_data = adev->driver_data;
- struct ec_event *event;
- struct ec_event_entry *entry, *oldest_entry;
- size_t event_size, num_words, word_size;
+ struct ec_event *event, *queue_event, *old_event;
+ size_t num_words, event_size;
u32 offset = 0;

while (offset < length) {
event = (struct ec_event *)(buf + offset);
- if (!event)
- return -EINVAL;

- /* Number of 16bit event data words is size - 1 */
- num_words = event->size - 1;
- word_size = num_words * sizeof(u16);
- event_size = sizeof(*event) + word_size;
+ num_words = ec_event_num_words(event);
+ event_size = ec_event_size(event);
if (num_words > EC_ACPI_MAX_EVENT_WORDS) {
dev_err(&adev->dev, "Too many event words: %zu > %d\n",
num_words, EC_ACPI_MAX_EVENT_WORDS);
return -EOVERFLOW;
- };
+ }

/* Ensure event does not overflow the available buffer */
if ((offset + event_size) > length) {
@@ -170,31 +238,15 @@ static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
/* Point to the next event in the buffer */
offset += event_size;

- /* Create event entry for the queue */
- entry = kzalloc(sizeof(struct ec_event_entry) + word_size,
- GFP_KERNEL);
- if (!entry)
+ /* Copy event into the queue */
+ queue_event = kmemdup(event, event_size, GFP_KERNEL);
+ if (!queue_event)
return -ENOMEM;
- entry->size = event_size;
- memcpy(&entry->event, event, entry->size);
-
- mutex_lock(&dev_data->lock);
-
- /* If the queue is full, delete the oldest event */
- if (dev_data->num_events >= MAX_NUM_EVENTS) {
- oldest_entry = list_first_entry(&dev_data->events,
- struct ec_event_entry,
- list);
- list_del(&oldest_entry->list);
- kfree(oldest_entry);
- dev_data->num_events--;
- }
-
- /* Add this event to the queue */
- list_add_tail(&entry->list, &dev_data->events);
- dev_data->num_events++;
-
- mutex_unlock(&dev_data->lock);
+ spin_lock(&dev_data->queue_lock);
+ old_event = event_queue_push(dev_data->events, queue_event);
+ spin_unlock(&dev_data->queue_lock);
+ kfree(old_event);
+ wake_up_interruptible(&dev_data->wq);
}

return 0;
@@ -210,7 +262,6 @@ static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
static void event_device_notify(struct acpi_device *adev, u32 value)
{
struct acpi_buffer event_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
- struct event_device_data *dev_data = adev->driver_data;
union acpi_object *obj;
acpi_status status;

@@ -249,9 +300,6 @@ static void event_device_notify(struct acpi_device *adev, u32 value)

enqueue_events(adev, obj->buffer.pointer, obj->buffer.length);
kfree(obj);
-
- if (dev_data->num_events)
- wake_up_interruptible(&dev_data->wq);
}

static int event_open(struct inode *inode, struct file *filp)
@@ -267,7 +315,7 @@ static int event_open(struct inode *inode, struct file *filp)

/* Increase refcount on device so dev_data is not freed */
get_device(&dev_data->dev);
- nonseekable_open(inode, filp);
+ stream_open(inode, filp);
filp->private_data = dev_data;

return 0;
@@ -281,7 +329,7 @@ static __poll_t event_poll(struct file *filp, poll_table *wait)
poll_wait(filp, &dev_data->wq, wait);
if (!dev_data->exist)
return EPOLLHUP;
- if (dev_data->num_events)
+ if (!event_queue_empty(dev_data->events))
mask |= EPOLLIN | EPOLLRDNORM | EPOLLPRI;
return mask;
}
@@ -293,8 +341,7 @@ static __poll_t event_poll(struct file *filp, poll_table *wait)
* @count: Number of bytes requested. Must be at least EC_ACPI_MAX_EVENT_SIZE.
* @pos: File position pointer, irrelevant since we don't support seeking.
*
- * Fills the passed buffer with the data from the first event in the queue,
- * removes that event from the queue. On error, the event remains in the queue.
+ * Removes the first event from the queue, places it in the passed buffer.
*
* If there are no events in the the queue, then one of two things happens,
* depending on if the file was opened in nonblocking mode: If in nonblocking
@@ -307,7 +354,7 @@ static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
loff_t *pos)
{
struct event_device_data *dev_data = filp->private_data;
- struct ec_event_entry *entry;
+ struct ec_event *event;
ssize_t n_bytes_written = 0;
int err;

@@ -315,39 +362,29 @@ static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
if (count != 0 && count < EC_ACPI_MAX_EVENT_SIZE)
return -EINVAL;

- mutex_lock(&dev_data->lock);
-
- while (dev_data->num_events == 0) {
- if (filp->f_flags & O_NONBLOCK) {
- mutex_unlock(&dev_data->lock);
+ spin_lock(&dev_data->queue_lock);
+ while (event_queue_empty(dev_data->events)) {
+ spin_unlock(&dev_data->queue_lock);
+ if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
- }
- /* Need to unlock so that data can actually get added to the
- * queue, and since we recheck before use and it's just
- * comparing pointers, this is safe unlocked.
- */
- mutex_unlock(&dev_data->lock);
+
err = wait_event_interruptible(dev_data->wq,
- dev_data->num_events);
+ !event_queue_empty(dev_data->events) ||
+ !dev_data->exist);
if (err)
return err;

/* Device was removed as we waited? */
if (!dev_data->exist)
return -ENODEV;
- mutex_lock(&dev_data->lock);
+ spin_lock(&dev_data->queue_lock);
}
-
- entry = list_first_entry(&dev_data->events,
- struct ec_event_entry, list);
- n_bytes_written = entry->size;
- if (copy_to_user(buf, &entry->event, n_bytes_written))
+ event = event_queue_pop(dev_data->events);
+ spin_unlock(&dev_data->queue_lock);
+ n_bytes_written = ec_event_size(event);
+ if (copy_to_user(buf, event, n_bytes_written))
n_bytes_written = -EFAULT;
- list_del(&entry->list);
- kfree(entry);
- dev_data->num_events--;
-
- mutex_unlock(&dev_data->lock);
+ kfree(event);

return n_bytes_written;
}
@@ -384,15 +421,13 @@ static void free_device_data(struct device *d)
struct event_device_data *dev_data;

dev_data = container_of(d, struct event_device_data, dev);
+ event_queue_free(dev_data->events);
kfree(dev_data);
}

static void hangup_device(struct event_device_data *dev_data)
{
- mutex_lock(&dev_data->lock);
dev_data->exist = false;
- mutex_unlock(&dev_data->lock);
-
/* Wake up the waiting processes so they can close. */
wake_up_interruptible(&dev_data->wq);
put_device(&dev_data->dev);
@@ -420,7 +455,7 @@ static int event_device_add(struct acpi_device *adev)
minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
if (minor < 0) {
error = minor;
- dev_err(&adev->dev, "Failed to find minor number: %d", error);
+ dev_err(&adev->dev, "Failed to find minor number: %d\n", error);
return error;
}

@@ -432,8 +467,13 @@ static int event_device_add(struct acpi_device *adev)

/* Initialize the device data. */
adev->driver_data = dev_data;
- INIT_LIST_HEAD(&dev_data->events);
- mutex_init(&dev_data->lock);
+ dev_data->events = event_queue_new(queue_size);
+ if (!dev_data->events) {
+ kfree(dev_data);
+ error = -ENOMEM;
+ goto free_minor;
+ }
+ spin_lock_init(&dev_data->queue_lock);
init_waitqueue_head(&dev_data->wq);
dev_data->exist = true;
atomic_set(&dev_data->available, 1);
@@ -496,14 +536,14 @@ static int __init event_module_init(void)

ret = class_register(&event_class);
if (ret) {
- pr_err(DRV_NAME ": Failed registering class: %d", ret);
+ pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
return ret;
}

/* Request device numbers, starting with minor=0. Save the major num. */
ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
if (ret) {
- pr_err(DRV_NAME ": Failed allocating dev numbers: %d", ret);
+ pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
goto destroy_class;
}
event_major = MAJOR(dev_num);
--
2.20.1
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