From fb775faa9e46ff481e4ced11116c9bd45359cb43 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Stefan=20B=C3=BChler?= <source@stbuehler.de>
Date: Fri, 19 Apr 2019 11:57:46 +0200
Subject: [PATCH] io_uring: fix poll full SQ detection
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io_uring_poll shouldn't signal EPOLLOUT | EPOLLWRNORM if the queue is
full; the old check would always signal EPOLLOUT | EPOLLWRNORM (unless
there were U32_MAX - 1 entries in the SQ queue).

Signed-off-by: Stefan Bühler <source@stbuehler.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 69910fd9ccca..b998e98acd01 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2576,7 +2576,8 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &ctx->cq_wait, wait);
 	/* See comment at the top of this file */
 	smp_rmb();
-	if (READ_ONCE(ctx->sq_ring->r.tail) + 1 != ctx->cached_sq_head)
+	if (READ_ONCE(ctx->sq_ring->r.tail) - ctx->cached_sq_head !=
+	    ctx->sq_ring->ring_entries)
 		mask |= EPOLLOUT | EPOLLWRNORM;
 	if (READ_ONCE(ctx->cq_ring->r.head) != ctx->cached_cq_tail)
 		mask |= EPOLLIN | EPOLLRDNORM;
-- 
2.30.2