From: Hao Xu <howeyxu@xxxxxxxxxxx>
Add comments to explain why it is always under uring lock when
incrementing head in __io_kbuf_recycle. And rectify one comemnt about
kbuf consuming in iowq case.
Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
io_uring/kbuf.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 9cdbc018fd64..37f06456bf30 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -50,6 +50,13 @@ void __io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
if (req->flags & REQ_F_BUFFER_RING) {
if (req->buf_list) {
if (req->flags & REQ_F_PARTIAL_IO) {
+ /*
+ * if we reach here, uring_lock has been
+ ¦* holden. Because in iowq, we already
+ ¦* cleared req->buf_list to NULL when got
+ ¦* the buffer from the ring, which means
+ ¦* we cannot be here in that case.
+ */
req->buf_list->head++;
req->buf_list = NULL;
} else {
@@ -128,12 +135,13 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
if (issue_flags & IO_URING_F_UNLOCKED) {
/*
* If we came in unlocked, we have no choice but to consume the
- * buffer here. This does mean it'll be pinned until the IO
- * completes. But coming in unlocked means we're in io-wq
- * context, hence there should be no further retry. For the
- * locked case, the caller must ensure to call the commit when
- * the transfer completes (or if we get -EAGAIN and must poll
- * or retry).
+ * buffer here otherwise nothing ensures the buffer not being
+ * used by others. This does mean it'll be pinned until the IO
+ * completes though coming in unlocked means we're in io-wq
+ * context and there may be further retries in async hybrid mode.
+ * For the locked case, the caller must ensure to call the commit
+ * when the transfer completes (or if we get -EAGAIN and must
+ * poll or retry).
*/
req->buf_list = NULL;
bl->head++;
--
2.25.1
