[PATCH 5.11] io_uring: share fixed_file_refs b/w multiple rsrcs

[PATCH 5.11] io_uring: share fixed_file_refs b/w multiple rsrcs

[Pavel Begunkov]

Double fixed files for splice/tee are done in a nasty way, it takes 2
ref_node refs, and during the second time it blindly overrides
req->fixed_file_refs hoping that it haven't changed. That works because
all that is done under iouring_lock in a single go but is error-prone.

Bind everything explicitly to a single ref_node and take only one ref,
with current ref_node ordering it's guaranteed to keep all files valid
awhile the request is inflight.

That's mainly a cleanup + preparation for generic resource handling,
but also saves pcpu_ref get/put for splice/tee with 2 fixed files.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6e052011a186..8e769d3f96ca 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1039,6 +1039,16 @@ static inline void io_clean_op(struct io_kiocb *req)
 		__io_clean_op(req);
 }
 
+static inline void io_set_resource_node(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	if (!req->fixed_file_refs) {
+		req->fixed_file_refs = &ctx->file_data->node->refs;
+		percpu_ref_get(req->fixed_file_refs);
+	}
+}
+
 static bool io_match_task(struct io_kiocb *head,
 			  struct task_struct *task,
 			  struct files_struct *files)
@@ -1927,9 +1937,7 @@ static struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx,
 static inline void io_put_file(struct io_kiocb *req, struct file *file,
 			  bool fixed)
 {
-	if (fixed)
-		percpu_ref_put(req->fixed_file_refs);
-	else
+	if (!fixed)
 		fput(file);
 }
 
@@ -1941,7 +1949,8 @@ static void io_dismantle_req(struct io_kiocb *req)
 		kfree(req->async_data);
 	if (req->file)
 		io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
-
+	if (req->fixed_file_refs)
+		percpu_ref_put(req->fixed_file_refs);
 	io_req_clean_work(req);
 }
 
@@ -6344,10 +6353,7 @@ static struct file *io_file_get(struct io_submit_state *state,
 			return NULL;
 		fd = array_index_nospec(fd, ctx->nr_user_files);
 		file = io_file_from_index(ctx, fd);
-		if (file) {
-			req->fixed_file_refs = &ctx->file_data->node->refs;
-			percpu_ref_get(req->fixed_file_refs);
-		}
+		io_set_resource_node(req);
 	} else {
 		trace_io_uring_file_get(ctx, fd);
 		file = __io_file_get(state, fd);
@@ -6725,6 +6731,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	req->ctx = ctx;
 	req->flags = 0;
 	req->link = NULL;
+	req->fixed_file_refs = NULL;
 	/* one is dropped after submission, the other at completion */
 	refcount_set(&req->refs, 2);
 	req->task = current;
-- 
2.24.0

Re: [PATCH 5.11] io_uring: share fixed_file_refs b/w multiple rsrcs

[Jens Axboe]

On 11/18/20 12:57 PM, Pavel Begunkov wrote:
> Double fixed files for splice/tee are done in a nasty way, it takes 2
> ref_node refs, and during the second time it blindly overrides
> req->fixed_file_refs hoping that it haven't changed. That works because
> all that is done under iouring_lock in a single go but is error-prone.
> 
> Bind everything explicitly to a single ref_node and take only one ref,
> with current ref_node ordering it's guaranteed to keep all files valid
> awhile the request is inflight.
> 
> That's mainly a cleanup + preparation for generic resource handling,
> but also saves pcpu_ref get/put for splice/tee with 2 fixed files.

LGTM, applied, thanks.

-- 
Jens Axboe