io_uring: initialize percpu refcounters using PERCU_REF_ALLOW_REINIT

to #26323588

commit 214828962dead0c698f92b60ef97ce3c5fc2c8fe upstream.

Percpu reference counters should now be initialized with the
PERCPU_REF_ALLOW_REINIT in order to allow switching them to the
percpu mode from the atomic mode. This is exactly what
percpu_ref_reinit() called from __io_uring_register() is supposed to
do. So let's initialize percpu refcounters with the
PERCU_REF_ALLOW_REINIT flag.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -553,7 +553,8 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 		goto err;
 	__hash_init(ctx->cancel_hash, 1U << hash_bits);
 
-	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free, 0, GFP_KERNEL))
+	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
+			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
 		goto err;
 
 	ctx->flags = p->flags;