commit f011c9cf04c06f16b24f583d313d3c012e589e50 upstream.
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") Signed-off-by: Felix Moessbauer felix.moessbauer@siemens.com Link: https://lore.kernel.org/r/20240909150036.55921-1-felix.moessbauer@siemens.co... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 8ed2c65529714..6b6fd244233f8 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 {