1 files changed, 47 insertions, 73 deletions

diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
index c530476edba6..ac9fda1b5a72 100644
--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -30,6 +30,7 @@
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/kfifo.h>
 #include <linux/sched/signal.h>
 #include <linux/export.h>
 #include <linux/slab.h>
@@ -661,17 +662,12 @@ EXPORT_SYMBOL_GPL(hid_dump_device);
 /* enqueue string to 'events' ring buffer */
 void hid_debug_event(struct hid_device *hdev, char *buf)
 {
-        unsigned i;
         struct hid_debug_list *list;
         unsigned long flags;
 
         spin_lock_irqsave(&hdev->debug_list_lock, flags);
-        list_for_each_entry(list, &hdev->debug_list, node) {
-                for (i = 0; buf[i]; i++)
-                        list->hid_debug_buf[(list->tail + i) % HID_DEBUG_BUFSIZE] =
-                                buf[i];
-                list->tail = (list->tail + i) % HID_DEBUG_BUFSIZE;
-        }
+        list_for_each_entry(list, &hdev->debug_list, node)
+                kfifo_in(&list->hid_debug_fifo, buf, strlen(buf));
         spin_unlock_irqrestore(&hdev->debug_list_lock, flags);
 
         wake_up_interruptible(&hdev->debug_wait);
@@ -722,8 +718,7 @@ void hid_dump_input(struct hid_device *hdev, struct hid_usage *usage, __s32 valu
         hid_debug_event(hdev, buf);
 
         kfree(buf);
-        wake_up_interruptible(&hdev->debug_wait);
-
+        wake_up_interruptible(&hdev->debug_wait);
 }
 EXPORT_SYMBOL_GPL(hid_dump_input);
 
@@ -1083,8 +1078,8 @@ static int hid_debug_events_open(struct inode *inode, struct file *file)
                 goto out;
         }
 
-        if (!(list->hid_debug_buf = kzalloc(HID_DEBUG_BUFSIZE, GFP_KERNEL))) {
-                err = -ENOMEM;
+        err = kfifo_alloc(&list->hid_debug_fifo, HID_DEBUG_FIFOSIZE, GFP_KERNEL);
+        if (err) {
                 kfree(list);
                 goto out;
         }
@@ -1104,77 +1099,57 @@ static ssize_t hid_debug_events_read(struct file *file, char __user *buffer,
                 size_t count, loff_t *ppos)
 {
         struct hid_debug_list *list = file->private_data;
-        int ret = 0, len;
+        int ret = 0, copied;
         DECLARE_WAITQUEUE(wait, current);
 
         mutex_lock(&list->read_mutex);
-        while (ret == 0) {
-                if (list->head == list->tail) {
-                        add_wait_queue(&list->hdev->debug_wait, &wait);
-                        set_current_state(TASK_INTERRUPTIBLE);
-
-                        while (list->head == list->tail) {
-                                if (file->f_flags & O_NONBLOCK) {
-                                        ret = -EAGAIN;
-                                        break;
-                                }
-                                if (signal_pending(current)) {
-                                        ret = -ERESTARTSYS;
-                                        break;
-                                }
+        if (kfifo_is_empty(&list->hid_debug_fifo)) {
+                add_wait_queue(&list->hdev->debug_wait, &wait);
+                set_current_state(TASK_INTERRUPTIBLE);
+
+                while (kfifo_is_empty(&list->hid_debug_fifo)) {
+                        if (file->f_flags & O_NONBLOCK) {
+                                ret = -EAGAIN;
+                                break;
+                        }
 
-                                if (!list->hdev || !list->hdev->debug) {
-                                        ret = -EIO;
-                                        set_current_state(TASK_RUNNING);
-                                        goto out;
-                                }
+                        if (signal_pending(current)) {
+                                ret = -ERESTARTSYS;
+                                break;
+                        }
 
-                                /* allow O_NONBLOCK from other threads */
-                                mutex_unlock(&list->read_mutex);
-                                schedule();
-                                mutex_lock(&list->read_mutex);
-                                set_current_state(TASK_INTERRUPTIBLE);
+                        /* if list->hdev is NULL we cannot remove_wait_queue().
+                         * if list->hdev->debug is 0 then hid_debug_unregister()
+                         * was already called and list->hdev is being destroyed.
+                         * if we add remove_wait_queue() here we can hit a race.
+                         */
+                        if (!list->hdev || !list->hdev->debug) {
+                                ret = -EIO;
+                                set_current_state(TASK_RUNNING);
+                                goto out;
                         }
 
-                        set_current_state(TASK_RUNNING);
-                        remove_wait_queue(&list->hdev->debug_wait, &wait);
+                        /* allow O_NONBLOCK from other threads */
+                        mutex_unlock(&list->read_mutex);
+                        schedule();
+                        mutex_lock(&list->read_mutex);
+                        set_current_state(TASK_INTERRUPTIBLE);
                 }
 
-                if (ret)
-                        goto out;
+                __set_current_state(TASK_RUNNING);
+                remove_wait_queue(&list->hdev->debug_wait, &wait);
 
-                /* pass the ringbuffer contents to userspace */
-copy_rest:
-                if (list->tail == list->head)
+                if (ret)
                         goto out;
-                if (list->tail > list->head) {
-                        len = list->tail - list->head;
-                        if (len > count)
-                                len = count;
-
-                        if (copy_to_user(buffer + ret, &list->hid_debug_buf[list->head], len)) {
-                                ret = -EFAULT;
-                                goto out;
-                        }
-                        ret += len;
-                        list->head += len;
-                } else {
-                        len = HID_DEBUG_BUFSIZE - list->head;
-                        if (len > count)
-                                len = count;
-
-                        if (copy_to_user(buffer, &list->hid_debug_buf[list->head], len)) {
-                                ret = -EFAULT;
-                                goto out;
-                        }
-                        list->head = 0;
-                        ret += len;
-                        count -= len;
-                        if (count > 0)
-                                goto copy_rest;
-                }
-
         }
+
+        /* pass the fifo content to userspace, locking is not needed with only
+         * one concurrent reader and one concurrent writer
+         */
+        ret = kfifo_to_user(&list->hid_debug_fifo, buffer, count, &copied);
+        if (ret)
+                goto out;
+        ret = copied;
 out:
         mutex_unlock(&list->read_mutex);
         return ret;
@@ -1185,7 +1160,7 @@ static __poll_t hid_debug_events_poll(struct file *file, poll_table *wait)
         struct hid_debug_list *list = file->private_data;
 
         poll_wait(file, &list->hdev->debug_wait, wait);
-        if (list->head != list->tail)
+        if (!kfifo_is_empty(&list->hid_debug_fifo))
                 return EPOLLIN | EPOLLRDNORM;
         if (!list->hdev->debug)
                 return EPOLLERR | EPOLLHUP;
@@ -1200,7 +1175,7 @@ static int hid_debug_events_release(struct inode *inode, struct file *file)
         spin_lock_irqsave(&list->hdev->debug_list_lock, flags);
         list_del(&list->node);
         spin_unlock_irqrestore(&list->hdev->debug_list_lock, flags);
-        kfree(list->hid_debug_buf);
+        kfifo_free(&list->hid_debug_fifo);
         kfree(list);
 
         return 0;
@@ -1246,4 +1221,3 @@ void hid_debug_exit(void)
 {
         debugfs_remove_recursive(hid_debug_root);
 }
-