releases/5.1.6/io_uring-use-cpu_online-to-check-p-sq_thread_cpu-ins.patch

From ced24def005719e4038cfd777d965cb08f0a3bc9 Mon Sep 17 00:00:00 2001
From: Shenghui Wang <shhuiw@foxmail.com>
Date: Tue, 7 May 2019 16:03:19 +0800
Subject: io_uring: use cpu_online() to check p->sq_thread_cpu instead of
 cpu_possible()

[ Upstream commit 7889f44dd9cee15aff1c3f7daf81ca4dfed48fc7 ]

This issue is found by running liburing/test/io_uring_setup test.

When test run, the testcase "attempt to bind to invalid cpu" would not
pass with messages like:
   io_uring_setup(1, 0xbfc2f7c8), \
flags: IORING_SETUP_SQPOLL|IORING_SETUP_SQ_AFF, \
resv: 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000, \
sq_thread_cpu: 2
   expected -1, got 3
   FAIL

On my system, there is:
   CPU(s) possible : 0-3
   CPU(s) online   : 0-1
   CPU(s) offline  : 2-3
   CPU(s) present  : 0-1

The sq_thread_cpu 2 is offline on my system, so the bind should fail.
But cpu_possible() will pass the check. We shouldn't be able to bind
to an offline cpu. Use cpu_online() to do the check.

After the change, the testcase run as expected: EINVAL will be returned
for cpu offlined.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Shenghui Wang <shhuiw@foxmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 84efb8956734f..30a5687a17b65 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2334,7 +2334,7 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 							nr_cpu_ids);
 
 			ret = -EINVAL;
-			if (!cpu_possible(cpu))
+			if (!cpu_online(cpu))
 				goto err;
 
 			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
-- 
2.20.1