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From:   Usama Arif <usama.arif@bytedance.com>
To:     io-uring@vger.kernel.org, axboe@kernel.dk, asml.silence@gmail.com,
        linux-kernel@vger.kernel.org
Cc:     fam.zheng@bytedance.com, Usama Arif <usama.arif@bytedance.com>
Subject: [PATCH v6 5/5] io_uring: remove ring quiesce for io_uring_register
Date:   Fri,  4 Feb 2022 14:51:17 +0000
Message-Id: <20220204145117.1186568-6-usama.arif@bytedance.com>
In-Reply-To: <20220204145117.1186568-1-usama.arif@bytedance.com>
References: <20220204145117.1186568-1-usama.arif@bytedance.com>
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None of the opcodes in io_uring_register use ring quiesce
anymore. Hence io_register_op_must_quiesce always returns
false and io_ctx_quiesce is never called.

Signed-off-by: Usama Arif <usama.arif@bytedance.com>
---
 fs/io_uring.c | 83 ---------------------------------------------------
 1 file changed, 83 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a2ce2601d4de..ad8f84376955 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1292,18 +1292,6 @@ static inline unsigned int io_put_kbuf(struct io_kiocb *req)
 	return __io_put_kbuf(req);
 }
 
-static void io_refs_resurrect(struct percpu_ref *ref, struct completion *compl)
-{
-	bool got = percpu_ref_tryget(ref);
-
-	/* already at zero, wait for ->release() */
-	if (!got)
-		wait_for_completion(compl);
-	percpu_ref_resurrect(ref);
-	if (got)
-		percpu_ref_put(ref);
-}
-
 static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
 			  bool cancel_all)
 	__must_hold(&req->ctx->timeout_lock)
@@ -10993,66 +10981,6 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	return ret;
 }
 
-static bool io_register_op_must_quiesce(int op)
-{
-	switch (op) {
-	case IORING_REGISTER_BUFFERS:
-	case IORING_UNREGISTER_BUFFERS:
-	case IORING_REGISTER_FILES:
-	case IORING_UNREGISTER_FILES:
-	case IORING_REGISTER_FILES_UPDATE:
-	case IORING_REGISTER_EVENTFD:
-	case IORING_REGISTER_EVENTFD_ASYNC:
-	case IORING_UNREGISTER_EVENTFD:
-	case IORING_REGISTER_PROBE:
-	case IORING_REGISTER_PERSONALITY:
-	case IORING_UNREGISTER_PERSONALITY:
-	case IORING_REGISTER_ENABLE_RINGS:
-	case IORING_REGISTER_RESTRICTIONS:
-	case IORING_REGISTER_FILES2:
-	case IORING_REGISTER_FILES_UPDATE2:
-	case IORING_REGISTER_BUFFERS2:
-	case IORING_REGISTER_BUFFERS_UPDATE:
-	case IORING_REGISTER_IOWQ_AFF:
-	case IORING_UNREGISTER_IOWQ_AFF:
-	case IORING_REGISTER_IOWQ_MAX_WORKERS:
-		return false;
-	default:
-		return true;
-	}
-}
-
-static __cold int io_ctx_quiesce(struct io_ring_ctx *ctx)
-{
-	long ret;
-
-	percpu_ref_kill(&ctx->refs);
-
-	/*
-	 * Drop uring mutex before waiting for references to exit. If another
-	 * thread is currently inside io_uring_enter() it might need to grab the
-	 * uring_lock to make progress. If we hold it here across the drain
-	 * wait, then we can deadlock. It's safe to drop the mutex here, since
-	 * no new references will come in after we've killed the percpu ref.
-	 */
-	mutex_unlock(&ctx->uring_lock);
-	do {
-		ret = wait_for_completion_interruptible_timeout(&ctx->ref_comp, HZ);
-		if (ret) {
-			ret = min(0L, ret);
-			break;
-		}
-
-		ret = io_run_task_work_sig();
-		io_req_caches_free(ctx);
-	} while (ret >= 0);
-	mutex_lock(&ctx->uring_lock);
-
-	if (ret)
-		io_refs_resurrect(&ctx->refs, &ctx->ref_comp);
-	return ret;
-}
-
 static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			       void __user *arg, unsigned nr_args)
 	__releases(ctx->uring_lock)
@@ -11076,12 +11004,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			return -EACCES;
 	}
 
-	if (io_register_op_must_quiesce(opcode)) {
-		ret = io_ctx_quiesce(ctx);
-		if (ret)
-			return ret;
-	}
-
 	switch (opcode) {
 	case IORING_REGISTER_BUFFERS:
 		ret = io_sqe_buffers_register(ctx, arg, nr_args, NULL);
@@ -11186,11 +11108,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 		break;
 	}
 
-	if (io_register_op_must_quiesce(opcode)) {
-		/* bring the ctx back to life */
-		percpu_ref_reinit(&ctx->refs);
-		reinit_completion(&ctx->ref_comp);
-	}
 	return ret;
 }
 
-- 
2.25.1