[1/2] io_uring/io-wq: do not allow pinning outside of cpuset

Commit Message

Felix Moessbauer Sept. 10, 2024, 2:33 p.m. UTC

The io work queue polling threads are userland threads that just never
exit to the userland. By that, they are also assigned to a cgroup (the
group of the creating task).

When changing the affinity of the io_wq thread via syscall, we must only
allow cpumasks within the ambient limits. These are defined by the cpuset
controller of the cgroup (if enabled).

Fixes: da64d6db3bd3 ("io_uring: One wqe per wq")
Signed-off-by: Felix Moessbauer <[e-mail]>
---
 io_uring/io-wq.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

Comments

Jens Axboe Sept. 10, 2024, 2:55 p.m. UTC | #1

On 9/10/24 8:33 AM, Felix Moessbauer wrote:
> The io work queue polling threads are userland threads that just never
> exit to the userland. By that, they are also assigned to a cgroup (the
> group of the creating task).

They are not polling threads, they are just worker threads.

> When changing the affinity of the io_wq thread via syscall, we must only
> allow cpumasks within the ambient limits. These are defined by the cpuset
> controller of the cgroup (if enabled).

ambient limits? Not quite sure that's the correct term to use here.

Outside of commit message oddities, change looks good.

Patch

diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index f1e7c670add8..c7055a8895d7 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -13,6 +13,7 @@ 
 #include <linux/slab.h>
 #include <linux/rculist_nulls.h>
 #include <linux/cpu.h>
+#include <linux/cpuset.h>
 #include <linux/task_work.h>
 #include <linux/audit.h>
 #include <linux/mmu_context.h>
@@ -1322,17 +1323,29 @@  static int io_wq_cpu_offline(unsigned int cpu, struct hlist_node *node)
 
 int io_wq_cpu_affinity(struct io_uring_task *tctx, cpumask_var_t mask)
 {
+	cpumask_var_t allowed_mask;
+	int ret = 0;
+
 	if (!tctx || !tctx->io_wq)
 		return -EINVAL;
 
+	if (!alloc_cpumask_var(&allowed_mask, GFP_KERNEL))
+		return -ENOMEM;
+
 	rcu_read_lock();
-	if (mask)
-		cpumask_copy(tctx->io_wq->cpu_mask, mask);
-	else
-		cpumask_copy(tctx->io_wq->cpu_mask, cpu_possible_mask);
+	cpuset_cpus_allowed(tctx->io_wq->task, allowed_mask);
+	if (mask) {
+		if (cpumask_subset(mask, allowed_mask))
+			cpumask_copy(tctx->io_wq->cpu_mask, mask);
+		else
+			ret = -EINVAL;
+	} else {
+		cpumask_copy(tctx->io_wq->cpu_mask, allowed_mask);
+	}
 	rcu_read_unlock();
 
-	return 0;
+	free_cpumask_var(allowed_mask);
+	return ret;
 }
 
 /*