linux-kernel - [PATCH v2 2/4] io_uring: update kiocb->ki

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Date:   Mon, 21 Feb 2022 06:16:47 -0800
From:   Dylan Yudaken <dylany@...com>
To:     Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        <io-uring@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
        Dylan Yudaken <dylany@...com>
Subject: [PATCH v2 2/4] io_uring: update kiocb->ki_pos at execution time

Update kiocb->ki_pos at execution time rather than in io_prep_rw().
io_prep_rw() happens before the job is enqueued to a worker and so the
offset might be read multiple times before being executed once.

Ensures that the file position in a set of _linked_ SQEs will be only
obtained after earlier SQEs have completed, and so will include their
incremented file position.

Signed-off-by: Dylan Yudaken <dylany@...com>
---
 fs/io_uring.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1f9b4466c269..50b93ff2ee12 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3000,14 +3000,6 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		req->flags |= io_file_get_flags(file) << REQ_F_SUPPORT_NOWAIT_BIT;
 
 	kiocb->ki_pos = READ_ONCE(sqe->off);
-	if (kiocb->ki_pos == -1) {
-		if (!(file->f_mode & FMODE_STREAM)) {
-			req->flags |= REQ_F_CUR_POS;
-			kiocb->ki_pos = file->f_pos;
-		} else {
-			kiocb->ki_pos = 0;
-		}
-	}
 	kiocb->ki_flags = iocb_flags(file);
 	ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
 	if (unlikely(ret))
@@ -3074,6 +3066,19 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 	}
 }
 
+static inline void
+io_kiocb_update_pos(struct io_kiocb *req, struct kiocb *kiocb)
+{
+	if (kiocb->ki_pos == -1) {
+		if (!(req->file->f_mode & FMODE_STREAM)) {
+			req->flags |= REQ_F_CUR_POS;
+			kiocb->ki_pos = req->file->f_pos;
+		} else {
+			kiocb->ki_pos = 0;
+		}
+	}
+}
+
 static void kiocb_done(struct io_kiocb *req, ssize_t ret,
 		       unsigned int issue_flags)
 {
@@ -3662,6 +3667,8 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 		kiocb->ki_flags &= ~IOCB_NOWAIT;
 	}
 
+	io_kiocb_update_pos(req, kiocb);
+
 	ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), req->result);
 	if (unlikely(ret)) {
 		kfree(iovec);
@@ -3791,6 +3798,8 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		kiocb->ki_flags &= ~IOCB_NOWAIT;
 	}
 
+	io_kiocb_update_pos(req, kiocb);
+
 	ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), req->result);
 	if (unlikely(ret))
 		goto out_free;
-- 
2.30.2