io_uring: force creation of separate context for ATTACH_WQ and non-threads

Earlier kernels had SQPOLL threads that could share across anything, as
we grabbed the context we needed on a per-ring basis. This is no longer
the case, so only allow attaching directly if we're in the same thread
group. That is the common use case. For non-group tasks, just setup a
new context and thread as we would've done if sharing wasn't set. This
isn't 100% ideal in terms of CPU utilization for the forked and share
case, but hopefully that isn't much of a concern. If it is, there are
plans in motion for how to improve that. Most importantly, we want to
avoid app side regressions where sharing worked before and now doesn't.
With this patch, functionality is equivalent to previous kernels that
supported IORING_SETUP_ATTACH_WQ with SQPOLL.

Reported-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5c045a9f7ffe056027a08cd22c1716c47338c7e0..472eab7359f2a26c9d3c60e6be5e4653089f9c81 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -269,6 +269,7 @@ struct io_sq_data {
        unsigned                sq_thread_idle;
        int                     sq_cpu;
        pid_t                   task_pid;
+       pid_t                   task_tgid;
 
        unsigned long           state;
        struct completion       startup;
@@ -7112,6 +7113,10 @@ static struct io_sq_data *io_attach_sq_data(struct io_uring_params *p)
                fdput(f);
                return ERR_PTR(-EINVAL);
        }
+       if (sqd->task_tgid != current->tgid) {
+               fdput(f);
+               return ERR_PTR(-EPERM);
+       }
 
        refcount_inc(&sqd->refs);
        fdput(f);
@@ -7122,8 +7127,14 @@ static struct io_sq_data *io_get_sq_data(struct io_uring_params *p)
 {
        struct io_sq_data *sqd;
 
-       if (p->flags & IORING_SETUP_ATTACH_WQ)
-               return io_attach_sq_data(p);
+       if (p->flags & IORING_SETUP_ATTACH_WQ) {
+               sqd = io_attach_sq_data(p);
+               if (!IS_ERR(sqd))
+                       return sqd;
+               /* fall through for EPERM case, setup new sqd/task */
+               if (PTR_ERR(sqd) != -EPERM)
+                       return sqd;
+       }
 
        sqd = kzalloc(sizeof(*sqd), GFP_KERNEL);
        if (!sqd)
@@ -7833,6 +7844,7 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
                }
 
                sqd->task_pid = current->pid;
+               sqd->task_tgid = current->tgid;
                tsk = create_io_thread(io_sq_thread, sqd, NUMA_NO_NODE);
                if (IS_ERR(tsk)) {
                        ret = PTR_ERR(tsk);