Re: FAILED: patch "[PATCH] io_uring/sqpoll: do not allow pinning outside of cpuset" failed to apply to 5.15-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 10/1/24 1:19 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> git checkout FETCH_HEAD
> git cherry-pick -x f011c9cf04c06f16b24f583d313d3c012e589e50
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024100131-number-deface-36a6@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Here's one for 5.15-stable AND 5.10-stable, remember that any stable
io_uring backport for 5.15-stable also applies to 5.10-stable as they
use the same codebase.

-- 
Jens Axboe

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From 0ce44d871d55dc7067d6ef85553ba52510a04337 Mon Sep 17 00:00:00 2001
From: Felix Moessbauer <felix.moessbauer@siemens.com>
Date: Mon, 9 Sep 2024 17:00:36 +0200
Subject: [PATCH] io_uring/sqpoll: do not allow pinning outside of cpuset

The submit queue polling threads are userland threads that just never
exit to the userland. When creating the thread with IORING_SETUP_SQ_AFF,
the affinity of the poller thread is set to the cpu specified in
sq_thread_cpu. However, this CPU can be outside of the cpuset defined
by the cgroup cpuset controller. This violates the rules defined by the
cpuset controller and is a potential issue for realtime applications.

In b7ed6d8ffd6 we fixed the default affinity of the poller thread, in
case no explicit pinning is required by inheriting the one of the
creating task. In case of explicit pinning, the check is more
complicated, as also a cpu outside of the parent cpumask is allowed.
We implemented this by using cpuset_cpus_allowed (that has support for
cgroup cpusets) and testing if the requested cpu is in the set.

Fixes: 37d1e2e3642e ("io_uring: move SQPOLL thread io-wq forked worker")
Cc: stable@vger.kernel.org # 6.1+
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Link: https://lore.kernel.org/r/20240909150036.55921-1-felix.moessbauer@siemens.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8ed2c6552971..6b6fd244233f 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -56,6 +56,7 @@
 #include <linux/mm.h>
 #include <linux/mman.h>
 #include <linux/percpu.h>
+#include <linux/cpuset.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/bvec.h>
@@ -8746,10 +8747,12 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 			return 0;
 
 		if (p->flags & IORING_SETUP_SQ_AFF) {
+			struct cpumask allowed_mask;
 			int cpu = p->sq_thread_cpu;
 
 			ret = -EINVAL;
-			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
+			cpuset_cpus_allowed(current, &allowed_mask);
+			if (!cpumask_test_cpu(cpu, &allowed_mask))
 				goto err_sqpoll;
 			sqd->sq_cpu = cpu;
 		} else {
-- 
2.45.2