A common complaint is that using O_NONBLOCK files with io_uring can be a
bit of a pain. Be a bit nicer and allow normal retry IFF the file does
support async behavior. This makes it possible to use io_uring more
reliably with O_NONBLOCK files, for use cases where it either isn't
possible or feasible to modify the file flags.
Cc: stable@xxxxxxxxxxxxxxx
Reported--by: Dan Melnic <dmm@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
diff --git a/fs/io_uring.c b/fs/io_uring.c
index d306ef0f4c10..722af90c74f2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2843,7 +2843,8 @@ static bool io_file_supports_nowait(struct io_kiocb *req, int rw)
return __io_file_supports_nowait(req->file, rw);
}
-static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+ int rw)
{
struct io_ring_ctx *ctx = req->ctx;
struct kiocb *kiocb = &req->rw.kiocb;
@@ -2865,8 +2866,13 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
if (unlikely(ret))
return ret;
- /* don't allow async punt for O_NONBLOCK or RWF_NOWAIT */
- if ((kiocb->ki_flags & IOCB_NOWAIT) || (file->f_flags & O_NONBLOCK))
+ /*
+ * If the file is marked O_NONBLOCK, still allow retry for it if it
+ * supports async. Otherwise it's impossible to use O_NONBLOCK files
+ * reliably. If not, or it IOCB_NOWAIT is set, don't retry.
+ */
+ if ((kiocb->ki_flags & IOCB_NOWAIT) ||
+ ((file->f_flags & O_NONBLOCK) && !io_file_supports_nowait(req, rw)))
req->flags |= REQ_F_NOWAIT;
ioprio = READ_ONCE(sqe->ioprio);
@@ -3354,7 +3360,7 @@ static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
if (unlikely(!(req->file->f_mode & FMODE_READ)))
return -EBADF;
- return io_prep_rw(req, sqe);
+ return io_prep_rw(req, sqe, READ);
}
/*
@@ -3557,7 +3563,7 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
if (unlikely(!(req->file->f_mode & FMODE_WRITE)))
return -EBADF;
- return io_prep_rw(req, sqe);
+ return io_prep_rw(req, sqe, WRITE);
}
static int io_write(struct io_kiocb *req, unsigned int issue_flags)
--
Jens Axboe
