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authorHao Xu <howeyxu@tencent.com>2022-06-17 13:04:29 +0800
committerJens Axboe <axboe@kernel.dk>2022-06-22 11:32:28 -0600
commitf27d5dcd1e462914ff8ca69a53a4dbea6e7b5e62 (patch)
tree11640f16b481597f804b091cd2a3977667b3de3b
parent8c8a4601b7612baaa73dceef45b146bf92537ef5 (diff)
io_uring: kbuf: add comments for some tricky code
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@tencent.com> Link: https://lore.kernel.org/r/20220617050429.94293-1-hao.xu@linux.dev Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--io_uring/kbuf.c20
1 files changed, 14 insertions, 6 deletions
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 07dbb0d17aae..d641d1f9450f 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -52,6 +52,13 @@ 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 end up here, then the io_uring_lock has
+ * been kept held since we retrieved the buffer.
+ * For the io-wq case, we already cleared
+ * req->buf_list when the buffer was retrieved,
+ * hence it cannot be set here for that case.
+ */
req->buf_list->head++;
req->buf_list = NULL;
} else {
@@ -163,12 +170,13 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
if (issue_flags & IO_URING_F_UNLOCKED || !file_can_poll(req->file)) {
/*
* 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 that the buffer won't
+ * get used by others. This does mean it'll be pinned until the
+ * IO completes, coming in unlocked means we're being called from
+ * io-wq context and there may be further retries in async hybrid
+ * mode. For the locked case, the caller must call commit when
+ * the transfer completes (or if we get -EAGAIN and must poll of
+ * retry).
*/
req->buf_list = NULL;
bl->head++;