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Subject[PATCH 3/3] kernel/watch_queue: Remove wqueue->defunct and use pipe for clear check
Date
The sole use of wqueue->defunct is for checking if the watch queue has
been cleared, but wqueue->pipe is also NULL'd while clearing.

Thus, wqueue->defunct is superfluous, as wqueue->pipe can be checked
for NULL.

Signed-off-by: Siddh Raman Pant <code@siddh.me>
---
include/linux/watch_queue.h | 3 +--
kernel/watch_queue.c | 14 +++++---------
2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index c99c39ec6548..2a3b318db49d 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -55,7 +55,7 @@ struct watch_filter {
*
* @rcu: RCU head
* @filter: Filter on watch_notification::info
- * @pipe: The pipe we're using as a buffer.
+ * @pipe: The pipe we're using as a buffer, NULL when queue is cleared/closed
* @watches: Contributory watches
* @notes: Preallocated notifications
* @notes_bitmap: Allocation bitmap for notes
@@ -63,7 +63,6 @@ struct watch_filter {
* @lock: Spinlock
* @nr_notes: Number of notes
* @nr_pages: Number of pages in notes[]
- * @defunct: True when queues closed
*/
struct watch_queue {
struct rcu_head rcu;
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 8999c4e3076d..c63b128818f4 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -43,7 +43,7 @@ MODULE_LICENSE("GPL");
static inline bool lock_wqueue(struct watch_queue *wqueue)
{
spin_lock_bh(&wqueue->lock);
- if (unlikely(wqueue->defunct)) {
+ if (unlikely(READ_ONCE(wqueue->pipe) == NULL)) {
spin_unlock_bh(&wqueue->lock);
return false;
}
@@ -99,15 +99,12 @@ static bool post_one_notification(struct watch_queue *wqueue,
struct watch_notification *n)
{
void *p;
- struct pipe_inode_info *pipe = READ_ONCE(wqueue->pipe);
+ struct pipe_inode_info *pipe = wqueue->pipe;
struct pipe_buffer *buf;
struct page *page;
unsigned int head, tail, mask, note, offset, len;
bool done = false;

- if (!pipe)
- return false;
-
spin_lock_irq(&pipe->rd_wait.lock);

mask = pipe->ring_size - 1;
@@ -603,10 +600,9 @@ void watch_queue_clear(struct watch_queue *wqueue)
rcu_read_lock();
spin_lock_bh(&wqueue->lock);

- /* Prevent new notifications from being stored. */
- wqueue->defunct = true;
-
- /* This pipe will get freed by caller, and we are anyways clearing. */
+ /* This pipe will get freed by the caller free_pipe_info().
+ * Removing this reference also prevents new notifications.
+ */
wqueue->pipe = NULL;

while (!hlist_empty(&wqueue->watches)) {
--
2.35.1

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