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Subject[PATCH 3/3] HID: debug: fix the ring buffer writer implementation
Date
ring buffer implementation hid_debug_event() is strange allowing a lost
of data. it does not move head pointer on append and uses per-byte for()
loop. fix this by introducing a new ring buffer implementation, which
overwrites the oldest data in case of the ring buffer overflow. it uses
some calculations for the buffer pointers but only 2 or less memcpy()
calls.

Signed-off-by: Vladis Dronov <vdronov@redhat.com>
---
drivers/hid/hid-debug.c | 66 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 58 insertions(+), 8 deletions(-)

diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
index de640e4132c7..63247ac4a9ce 100644
--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -661,20 +661,70 @@ 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, flags2;
+ unsigned long flags1, flags2;
+ unsigned int part1, part2;
+ size_t len;

- spin_lock_irqsave(&hdev->debug_list_lock, flags);
+ if (!buf || !buf[0])
+ return;
+
+ len = strlen(buf);
+
+ spin_lock_irqsave(&hdev->debug_list_lock, flags1);
list_for_each_entry(list, &hdev->debug_list, node) {
spin_lock_irqsave(&list->list_lock, flags2);
- 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;
+
+ /* len >= BUFSIZE, copy the last HID_DEBUG_BUFSIZE-1 bytes */
+ if (len > HID_DEBUG_BUFSIZE - 1) {
+ memcpy(list->hid_debug_buf,
+ buf + len - (HID_DEBUG_BUFSIZE - 1),
+ HID_DEBUG_BUFSIZE - 1);
+
+ list->head = 0;
+ list->tail = HID_DEBUG_BUFSIZE - 1;
+ } else {
+ /* append data to the ring buffer */
+ part1 = min_t(size_t, HID_DEBUG_BUFSIZE - list->tail,
+ len);
+ part2 = len - part1;
+
+ memcpy(list->hid_debug_buf + list->tail, buf, part1);
+
+ /* check if head must be moved as the ring is full */
+ if ((list->tail < list->head) &&
+ (list->tail + part1 >= list->head)) {
+ list->head = list->tail + part1 + 1;
+
+ if (list->head >= HID_DEBUG_BUFSIZE)
+ list->head -= HID_DEBUG_BUFSIZE;
+ }
+
+ /* set tail after the end of appended data */
+ list->tail = list->tail + part1;
+ if (list->tail == HID_DEBUG_BUFSIZE) {
+ list->tail = 0;
+ if (list->head == 0)
+ list->head = 1;
+ }
+
+ /* append the 2nd part of data to the ring */
+ if (part2 > 0) {
+ memcpy(list->hid_debug_buf, buf + part1, part2);
+
+ /* check if head must be moved again as
+ * the ring is full
+ */
+ if (list->tail + part2 >= list->head)
+ list->head = list->tail + part2 + 1;
+
+ list->tail = list->tail + part2;
+ }
+ }
+
spin_unlock_irqrestore(&list->list_lock, flags2);
}
- spin_unlock_irqrestore(&hdev->debug_list_lock, flags);
+ spin_unlock_irqrestore(&hdev->debug_list_lock, flags1);

wake_up_interruptible(&hdev->debug_wait);
}
--
2.19.0
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