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io_uring: don't use poll handler if file can't be nonblocking read/written

PATCH New Jens Axboe 1 participant 1 message Aug 25, 2020

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Jens Axboe

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PATCH 1/1 io_uring: don't use poll handler if file can't be nonblocking read/written

There's no point in using the poll handler if we can't do a nonblocking IO attempt of the operation, since we'll need to go async anyway. In fact this is actively harmful, as reading from eg pipes won't return 0 to indicate EOF.

Cc [email protected] # v5.7+
Signed-off-by Jens Axboe <[email protected]>

---

fs/io_uring.c +9 -1
index 384df86dfc69..d15139088e4c 100644
@@ -4889,12 +4889,20 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
 	struct async_poll *apoll;
 	struct io_poll_table ipt;
 	__poll_t mask, ret;
+	int rw;
 
 	if (!req->file || !file_can_poll(req->file))
 		return false;
 	if (req->flags & REQ_F_POLLED)
 		return false;
-	if (!def->pollin && !def->pollout)
+	if (def->pollin)
+		rw = READ;
+	else if (def->pollout)
+		rw = WRITE;
+	else
+		return false;
+	/* if we can't nonblock try, then no point in arming a poll handler */
+	if (!io_file_supports_async(req->file, rw))
 		return false;
 
 	apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
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Jens Axboe